shielded metal-arc welding and wearfacing

shielded metal-arc welding and wearfacing
CHAPTER 7
SHIELDED METAL-ARC WELDING
AND WEARFACING
requires a number of accessories that include a combination chipping hammer and wire brush, welding table
(for shopwork), C-clamps, and protective apparel.
The shielded metal-arc welding process, referred to
as metallic-arc welding, arc welding, or stick welding,
is extensively used in welding ferrous and nonferrous
metals. It has many applications for producing a vast
assortment of metal products. Shielded metal-arc welding is found in the ship building industry and in the
construction industry for fabricating girders, beams, and
columns. Because it is easy to use and portable, shielded
metal-arc welding is universally used in the repair and
servicing of equipment, machinery, and a host of other
items.
Before we discuss the different types of welding
machines, you must first have a basic knowledge of the
electrical terms used with welding.
Electrical Terms
Many terms are associated with arc welding. The
following basic terms are especially important.
ALTERNATING CURRENT.— Alternating current is an electrical current that has alternating negative
and positive values. In the first half-cycle, the current
flows in one direction and then reverses itself for the
next half-cycle. In one complete cycle, the current
spends 50 percent of the time flowing one way and the
other 50 percent flowing the other way. The rate of
change in direction is called frequency, and it is indicated by cycles per second. In the United States, the
alternating current is set at 60 cycles per second.
MANUAL SHIELDED METAL-ARC
WELDING
Arc welding provides you the ability to join two
metals by melting them with an arc generated between
a coated-metal electrode and the base metal. The temperatures developed by the arc can reach as high as
10000°F. The arc energy is provided by a power source
that generates either direct or alternating current. The
electrodes that carry the current produce a gas that
shields the arc from the atmosphere and supplies filler
metal to develop the weld shape.
AMPERE.— Amperes, sometimes called “amps,”
refers to the amount of current that flows through a
circuit. It is measured by an “amp” meter.
ARC-WELDING EQUIPMENT
CONDUCTOR.— Conductor means any material
that allows the passage of an electrical current.
A wide variety of welding equipment is available,
and there are many differences between the makes and
models of the equipment produced by the manufacturers. However, all types of arc-welding equipment are
similar in their basic function of producing the high-amperage, low-voltage electric power required for the
welding arc. In this discussion, we are primarily concerned with the typical items of arc-welding equipment,
rather than the specific types. For specific information
about the equipment your battalion or duty station has
available, consult the manufacturer’s instruction manual. For additional operational information and safety
instruction, have your leading welding petty officer
explain the operation to you.
CURRENT.— Current is the movement or flow of
an electrical charge through a conductor.
DIRECT CURRENT.— Direct current is an electrical current that flows in one direction only.
ELECTRICAL CIRCUIT.— Electrical circuit is
the path taken by an electrical current flowing through
a conductor from one terminal of the source to the load
and returning to the other terminal of the source.
POLARITY.— Polarity is the direction of the flow
of current in a circuit. Since current flows in one direction only in a dc welder, the polarity becomes an important factor in welding operations.
The basic parts of a typical shielded metal-arc welding outfit include a welding machine, cables, electrode
holder (stinger), and electrodes. The Steelworker also
RESISTANCE.— Resistance is the opposition of
the conductor to the flow of current. Resistance causes
electrical energy to be changed into heat.
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127.517
Figure 7-1.—A 300 amp ac/dc portable welding
machine.
Figure 7-2.—An ac arc-welding transformer.
1. Machines rated 150 and 200 amperes—30 volts
are for light-shielded metal-arc welding and for inertgas arc welding. They are also for general-purpose
jobs or shopwork.
VOLT.— A volt is the force required to make the
current flow in an electrical circuit. It can be
compared to pressure in a hydraulic system. Volts are
measured with a volt meter.
2. Machines rated 200,300, and 400 amperes—40
volts are for general welding purposes by machine or
manual application.
Power Source
The power source used in arc welding is called a
welding machine or a welder. Three basic types of
welding machines are presently in use: motorgenerators, transformers, and rectifiers.
3. Machines rated 600 amperes—40 volts are for
submerged-arc welding or carbon-arc cutting.
ALTERNATING-CURRENT TRANSFORMER
WELDING MACHINES.— Practically all the
alternating current (at) arc-welding machines in use
are the static-transformer type, as shown in figure 72. These types of machines are the smallest, least
expensive, and the lightest type of welders made.
Industrial applications for manual operation use
machines having 200, 300, and 400 ampere ratings.
Machines with a 150-ampere rating are used in light
industrial, garage, and job/shop welding.
The transformers are usually equipped with arcstabilizing capacitors. Current control is provided in
several
ways
by
the
welding
transformer
manufacturers. One such method is an adjustable
reactor that is set by turning a crank until the
appropriate setting is found. Another method is by
plugging the electrode cable into different sockets
located on the front of the machine.
One major advantage of ac transformers is the
freedom from arc blow, which often occurs when welding
with direct-current (dc) machines. Arc blow causes the arc
to wander while you are welding in corners on heavy
metal or using large coated electrodes.
MOTOR-GENERATOR
WELDING
MACHINES.— These types of welding machines are
powered by electrical, gasoline, or diesel motors. The
diesel and gasoline motors are ideal for use in areas
where electricity is not available. Portable gas/diesel
welding machines are part of the equipment
allowance for Naval Mobile Construction Battalions.
These machines usually have the capability of
generating alternating or direct current. On the
newer machines, when you are welding in the directcurrent mode, the polarity can be changed by turning
a switch. Some of the older machines require
reversing the cable connections. One of the
advantages of a direct-current (dc) welding generator
is that you have the choice of welding with either
straight or reverse polarity. The welding machine, as
shown in figure 7-1, consists of a heavy-duty, ac/dc
300 amp generator powered by a diesel engine. The
generator is also capable of producing 3 kilowatts of
60 cycle ac power.
Welding machines are made in six standardized
ratings for general purposes and are listed as follows:
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Table 7-1.—Cable Size Selection Guide
polarity current. By flicking a switch, the welder can
select the current that best suits the job. Figure 7-3 shows
an example of a combination ac/dc rectifier.
Cables
Welding cables carry the current to and from the
workpiece. One of the cables runs from the welding
machine to the electrode holder and the other cable
connects the workpiece to the welding machine. The
cable that connects the workpiece to the welding machine is called the ground. When the machine is turned
on and the operator touches the electrode to the workpiece, the circuit is completed, current begins to flow,
and the welding process commences.
The welding cables must be flexible, durable, well
insulated, and large enough to carry the required current.
Only cable that is specifically designed for welding
should be used. A highly flexible cable must be used for
the electrode holder connection. This is necessary so the
operator can easily maneuver the electrode holder during the welding process. The ground cable need not be
so flexible because once it is connected, it does not
move.
Two factors determine the size of welding cable to
use: the amperage rating of the machine and the distance
between the work and the machine. If either amperage
or distance increases, the cable size also must increase.
(See table 7-1.) A cable that is too small for the amperage
or the distance between the machine and the work will
overheat. On the other hand, larger size cables are more
Figure 7-3.—Combination ac, dc transformer-rectifier arc welder.
RECTIFIER WELDING MACHINES.— Rectifier welders are single-phase or three-phase transformers that have selenium or silicon rectifiers added to
rectify (change) the output current from alternating to
direct current. Most of these machines have the capability of producing either ac or dc straight or reverse
7-3
difficult to handle, especially if you are working on a
structure that requires a lot of moving around. The best
size cable is one that meets the amperage demand but is
small enough to manipulate with ease.
As a rule, the cable between the machine and the
work should be as short as possible. Use one continuous
length of cable if the distance is less than 35 feet. If you
must use more than one length of cable, join the sections
with insulated lock-type cable connectors. Joints in the
cable should be at least 10 feet away from the operator.
Figure 7-4.—C-clamped ground cable.
Electrode Holder
An electrode holder, commonly called a stinger, is
a clamping device for holding the electrode securely in
any position. The welding cable attaches to the holder
through the hollow insulated handle. The design of the
electrode holder permits quick and easy electrode exchange. Two general types of electrode holders are in
use: insulated and noninsulated. The noninsulated holders are not recommended because they are subject to
accidental short circuiting if bumped against the workpiece during welding. For safety reasons, try to ensure
the use of only insulated stingers on the jobsite.
Figure 7-5.—A spring-loaded ground clamp for the ground lead.
Electrode holders are made in different sizes, and
manufacturers have their own system of designation.
Each holder is designed for use within a specified range
of electrode diameters and welding current. You require
a larger holder when welding with a machine having a
300-ampere rating than when welding with a 100-ampere machine. If the holder is too small, it will overheat.
Ground Clamps
Figure 7-6.—Bolted and tack-welded ground clamps.
The use of a good ground clamp is essential to
producing quality welds. Without proper grounding, the
circuit voltage fails to produce enough heat for proper
welding, and there is the possibility of damage to the
welding machine and cables. Three basic methods are
used to ground a welding machine. You can fasten the
ground cable to the workbench with a C-clamp (fig. 74), attach a spring-loaded clamp (fig. 7-5) directly onto
the workpiece, or bolt or tack-weld the end of the ground
cable to the welding bench (fig. 7-6). The third way
creates a permanent common ground.
part of the welder’s equipment. After initial cleaning and
a weld bead has been deposited, the slag cover must be
removed before additional beads are added. The chipping hammer was specifically designed for this task.
The chipping operation is then followed by more brushing, and this cycle is repeated until the slag has been
removed. When the slag is not removed, the result is
porosity in the weld that weakens the weld joint.
Cleaning can also be accomplished by the use of
power tools or chemical agents. If these items are used,
it is essential that all safety precautions are followed.
Cleaning Equipment
Safety Equipment
Strong welds require good preparation and procedure. The surface area of the workpiece must be free of
all foreign material, such as rust, paint, and oil. A steel
brush is an excellent cleaning tool and is an essential
Arc welding not only produces a brilliant light, but
it also emits ultraviolet and infrared rays that are very
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dangerous to your eyes and skin. In chapter 3, personal
safety items, such as helmets, lenses, and gloves, were
covered. An important item that needs to be covered
here is welding screens. The welder not only has to
protect himself but he also must take precautions to
protect other people who may be working close by.
When you are welding in the field, you must install a
welding screen around your work area. It can be an
elaborate factory-manufactured screen or as simple as
one constructed on site from heavy fire-resistant canvas.
literature and check with your senior petty officer or
chief on the items that you do not understand. Machine
setup involves selecting current type, polarity, and current settings. The current selection depends on the size
and type of electrode used, position of the weld, and the
properties of the base metal.
Cable size and connections are determined by the
distance required to reach the work the size of the
machine, and the amperage needed for the weld.
Operator maintenance depends on the type of welding machine used. Transformers and rectifiers require
little maintenance compared to engine-driven welding
machines. Transformer welders require only to be kept
dry and a minimal amount of cleaning. Internal maintenance should only be done by electricians due to the
possibilities of electrical shock Engine-driven machines require daily maintenance of the motors. Inmost
places you will be required to fill out and turn in a daily
inspection form called a “hard card” before starting the
engine. This form is a list of items, such as oil level,
water level, visible leaks, and other things, that affect
the operation of the machine. Transportation departments are the ones who usually handle these forms.
WARNING
Never look at thes welding arc without
proper eye protection. Looking at the arc with
the naked eye could result in permanent eye
damage. If you receive flash burns, they should
be treated by medical personnel.
Another area often overlooked is ventilation. Welding produces a lot of smoke and fumes that can be
injurious to the welder if they are allowed to accumulate.
This is especially true if you are welding in a tank or
other inclosed area. Permanent welding booths should
be equipped with a exhaust hood and fan system for
removal of smoke and fumes.
After all of the above items have been checked, you
are now ready to start welding.
EQUIPMENT OPERATION AND
MAINTENANCE
SHIELDED-METAL ARC WELDING
Learning to arc weld requires you to possess many
skills. Among these skills are the abilities to set up,
operate, and maintain your welding equipment.
Before you start to weld, ensure that you have all
the required equipment and accessories. Listed below
are some additional welding rules that should be followed.
WELDING AREA REQUIREMENTS
Clear the welding area of all debris and clutter.
In most factory environments, the work is brought
to the welder. In the Seabees, the majority of the time
the opposite is true. You will be called to the field for
welding on buildings, earthmoving equipment, well
drilling pipe, ship to shore fuel lines, pontoon causeways, and the list goes on. To accomplish these tasks,
you have to become familiar with your equipment and
be able to maintain it in the field. It would be impossible
to give detailed maintenance information here because
of the many different types of equipment found in the
field; therefore, only the highlights will be covered.
Do not use gloves or clothing that contains oil or
grease.
Check that all wiring and cables are installed
properly.
Ensure that the machine is grounded and dry.
Follow all manufacturer’s directions on operating the welding machine.
Have on hand a protective screen to protect
others in the welding area from FLASH bums.
WELDING MACHINE OPERATION
AND MAINTENANCE
Always keep fire-fighting equipment on hand.
You should become familiar with the welding machine that you will be using. Study the manufacturer’s
Clean rust, scale, paint, or dirt from the joints
that are to be welded.
7-5
Figure 7-7.—Electrode covering and gaseous shield that protects
weld metal from the atmosphere.
ELECTRODES
In general, all electrodes are classified into five
main groups:
1. Mild steel
Figure 7-8.—Explanation of AWS classification numbers.
2. High-carbon steel
3. Special alloy steel
the molten metal from oxidation or contamination by the
surrounding atmosphere.
As molten metal is deposited in the welding process,
it attracts oxygen and nitrogen. Since the arc stream
takes place in the atmosphere, oxidation occurs while
the metal passes from the electrode to the work. When
this happens, the strength and ductility of the weld are
reduced as well as the resistance to corrosion. The
coating on the electrode prevents oxidation from taking
place. As the electrode melts, the heavy coating releases
an inert gas around the molten metal that excludes the
atmosphere from the weld (fig. 7-7).
The burning residue of the coating forms a slag over
the deposited metal that slows down the cooling rate and
produces a more ductile weld. Some coatings include
powdered iron that is converted to steel by the intense
heat of the arc as it flows into the weld deposit.
4. Cast iron
5. Nonferrous
The widest range of arc welding is done with electrodes
in the mild steel group.
Electrodes are manufactured for use in specific
positions and for many different types of metal. They
also are specially designed to use with ac or dc welding
machines. Some manufacturer’s electrodes work identically on either ac or dc, while others are best suited for
flat-position welding. Another type is made primarily
for vertical and overhead welding, and some can be used
in any position. As you can see, electrode selection
depends on many variables.
Types of Electrodes
Electrodes are classified as either bare or shielded.
The original bare electrodes were exactly as their name
implied—bare. Today, they have a light covering, but
even with this improvement they are rarely used because
of their limitations. They are difficult to weld with,
produce brittle welds, and have low strength. Just about
all welding is done with shielded electrodes.
The shielded electrode has a heavy coating of several chemicals, such as cellulose, titania sodium, lowhydrogen sodium, or iron powder. Each of the chemicals
in the coating serves a particular function in the welding
process. In general, their main purposes are to induce
easier arc starting, stabilize the arc, improve weld
appearance and penetration, reduce spatter, and protect
Electrode Identification
Electrodes are often referred to by a manufacturer’s
trade name. The American Welding Society (AWS) and
the American Society foresting and Materials (ASTM)
have set up certain requirements for electrodes to assure
some degree of uniformity in manufacturing electrodes.
Thus different manufacturer’s electrodes that are within
the classification established by the AWS and ASTM
should have the same welding characteristics. (See
fig. 7-8.)
In this classification, each type of electrode is
assigned a specific symbol, such as E-6010, E-7010, and
E-8010. The prefix E identifies the electrode for
7-6
Table 7-2.—Electrode Selection Guide
The fourth digit of the symbol represents special
characteristics of the electrode, such as weld quality,
type of current, and amount of penetration. The numbers
range from 0 through 8. Since the welding position is
dependent on the manufacturer’s characteristics of the
coating, the third and fourth numbers are often identified
together.
electric-arc welding. The first two digits in the symbol
designate the minimum allowable tensile strength in
thousands of pounds per square inch of the deposited
weld metal. For example, the 60-series electrodes have
a minimum tensile strength of 60,000 pounds per square
inch, while the 70-series electrodes have a strength of
70,000 pounds per square inch.
The third digit of the symbol indicates the joint
position for which the electrode is designed. Two numhers are used for this purpose: 1 and 2. Number 1 designates an electrode that can be used for welding in any
position. Number 2 represents an electrode restricted for
welding in the horizontal and flat positions only.
Electrode Selection
Several factors are critical when you choose an
electrode for welding. The welding position is particularly significant. Table 7-2 shows the recommended
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current types and welding positions for the most common electrodes.
As a rule of thumb, you should never use an electrode that has a diameter larger than the thickness of the
metal that you are welding. Some operators prefer larger
electrodes because they permit faster travel, but this
takes a lot of expedience to produce certified welds.
Position and the type of joint are also factors in
determining the size of the electrode. For example, in a
thick-metal section with a narrow vee, a small-diameter
electrode is always used to run the frost weld or root pass.
This is done to ensure full penetration at the root of the
weld. Successive passes are then made with larger electrodes.
For vertical and overhead welding, 3/16 inch is the
largest diameter electrode that you should use regardless
of plate thickness. Larger electrodes make it too difficult
to control the deposited metal. For economy, you should
always use the largest electrode that is practical for the
work It takes about one half of the time to deposit an
equal quantity of weld metal from 1/4-inch electrodes
as it does from 3/16-inch electrodes of the same type.
The larger sizes not only allow the use of higher currents
but also require fewer stops to change electrodes.
Deposit rate and joint preparation are also important
in the selection of an electrode. Electrodes for welding
mild steel can be classified as fast freeze, fill freeze, and
fast fill. FAST-FREEZE electrodes produce a snappy,
deep penetrating arc and fast-freezing deposits. They are
commonly called reverse-polarity electrodes, even
though some can be used on ac. These electrodes have
little slag and produce flat beads. They are widely used
for all-position welding for both fabrication and repair
work
FILL-FREEZE electrodes have a moderately forceful arc and a deposit rate between those of the fast-freeze
and fast-fill electrodes. They are commonly called the
straight-polarity electrodes, even though they may be
used on ac. These electrodes have complete slag coverage and weld deposits with distinct, even ripples. They
are the general-purpose electrode for a production shop
and are also widely used for repair work They can be
used in all positions, but fast-freeze electrodes are still
preferred for vertical and overhead welding.
Among the FAST-FILL electrodes are the heavycoated, iron powder electrodes with a soft arc and fast
deposit rate. These electrodes have a heavy slag and
produce exceptionally smooth weld deposits. They are
generally used for production welding where the work
is positioned for flat welding.
Another group of electrodes are the low-hydrogen
type that were developed for welding high-sulfur and
high-carbon steel. These electrodes produce X-ray
quality deposits by reducing the absorption of hydrogen
that causes porosity and cracks under the weld bead.
Welding stainless steel requires an electrode containing chromium and nickel. All stainless steels have
low-thermal conductivity that causes electrode overheating and improper arc action when high currents are
used. In the base metal, it causes large temperature
differentials between the weld and the rest of the work,
which warps the plate. A basic rule in welding stainless
steel is to avoid high currents and high heat. Another
reason for keeping the weld cool is to avoid carbon
corrosion.
There are also many special-purpose electrodes for
surfacing and welding copper and copper alloys, aluminum, cast iron, manganese, nickel alloys, and nickelmanganese steels. The composition of these electrodes
is designed to match the base metal. The basic rule in
selecting electrodes is to pick one that is similar in
composition to the base metal.
Electrode Storage
Electrodes are expensive; therefore, the loss or deterioration through improper handling or storage can
become very costly. Always store them in a dry place at
room temperature with 50-percent maximum relative
humidity. Moisture causes the coating on electrodes to
disintegrate and fall off. Low-hydrogen rods are especially sensitive to moisture. After removing these rods
from their original packaging, you should store them in
a storage space maintained at a temperature between
250°F to 400°F. Portable or stationary drying ovens are
used to store and preserve electrodes at specified temperatures. Care should be taken when handling electrodes because bumping or dropping them can cause the
coatings to fall off, rendering the rod useless.
Polarity
Earlier in this chapter, ac and dc current was briefly
covered. With ac welding machines, polarity is not a
problem. When using dc welding machines, you can
weld with either straight polarity or reverse polarity.
Polarity is the direction of the current flow in a
circuit, as shown in figure 7-9. In straight polarity, the
electrode is negative and the workpiece positive; the
electrons flow from the electrode to the workpiece. In
reverse polarity, the electrode is positive and the workpiece negative; the electrons flow from the workpiece
to the electrode. To help you remember the difference,
think of straight polarity as a SENator and reverse
polarity as a REPresentative. Use only the first three
letters of each key word. SEN stands for Straight Electrode Negative; REP for Reverse Electrode Positive.
7-8
Figure 7-10.—Striking or brushing method of starting the arc.
opposite is true and the greatest heat is produced on the
negative side. Electrode coatings affect the heat conditions differently. One type of heavy coating may provide
the most desirable heat balance with straight polarity,
while another type of coating on the same electrode may
provide a more desirable heat balance with reverse
polarity.
Reverse polarity is used in the welding of nonferrous metals, such as aluminum, bronze, Monel, and
nickel. Reverse polarity is also used with some types of
electrodes for making vertical and overhead welds.
You can recognize the proper polarity for a given
electrode by the sharp, crackling sound of the arc. The
wrong polarity causes the arc to emit a hissing sound,
and the welding bead is difficult to control.
One disadvantage of direct-current welding is “arc
blow.” As stated earlier, arc blow causes the arc to
wander while you are welding in corners on heavy metal
or when using large-coated electrodes. Direct current
flowing through the electrode, workpiece, and ground
clamp generates a magnetic field around each of these
units. This field can cause the arc to deviate from the
intended path. The arc is usually deflected forward or
backward along the line of travel and may cause excessive spatter and incomplete fusion. It also has the tendency to pull atmospheric gases into the arc, resulting
in porosity.
Arc blow can often be corrected by one of the
following methods: by changing the position of the
ground clamp, by welding away from the ground clamp,
or by changing the position of the workpiece.
Figure 7-9.—Straight and reverse polarity in electric welding.
On some of the older machines, polarity is changed
by switching cables. On many of the newer machines,
the polarity can be changed by turning a switch on the
machine.
Polarity affects the amount of heat going into the
base metal. By changing polarity, you can direct the
amount of heat to where it is needed. When you use
straight polarity, the majority of the heat is directed
toward the workpiece. When you use reverse polarity,
the heat is concentrated on the electrode. In some welding situations, it is desirable to have more heat on the
workpiece because of its size and the need for more heat
to melt the base metal than the electrode; therefore,
when making large heavy deposits, you should use
STRAIGHT POLARITY.
On the other hand, in overhead welding it is necessary to rapidly freeze the filler metal so the force of
gravity will not cause it to fall. When you use REVERSE
POLARITY, less heat is concentrated at the workpiece.
This allows the filler metal to cool faster, giving it
greater holding power. Cast-iron arc welding is another
good example of the need to keep the workpiece cool;
reverse polarity permits the deposits from the electrode
to be applied rapidly while preventing overheating in
the base metal.
In general, straight polarity is used for all mild steel,
bare, or lightly coated electrodes. With these types of
electrodes, the majority of heat is developed at the
positive side of the current, the workpiece. However,
when heavy-coated electrodes are used, the gases given
off in the arc may alter the heat conditions so the
STARTING THE ARC
Two basic methods are used for starting the arc: the
STRIKING or BRUSHING method (fig. 7-10) and the
7-9
After you strike the arc, the end of the electrode
melts and flows into the molten crater of the base metal.
To compensate for this loss of metal, you must adjust
the length of the arc. Unless you keep moving the
electrode closer to the base metal, the length of the arc
will increase. An arc that is too long will have a humming type of sound. One that is too short makes a
popping noise. When the electrode is fed down to the
plate and along the surface at a constant rate, a bead of
metal is deposited or welded onto the surface of the base
metal. After striking the arc, hold it for a short time at
the starting point to ensure good fusion and crater deposition. Good arc welding depends upon the control of
the motion of the electrode along the surface of the base
metal.
Setting the Current
Figure 7-11.—Tapping method of starting the arc.
The amount of current used during a welding operation depends primarily upon the diameter of the electrode. As a rule, higher currents and larger diameter
electrodes are better for welding in the flat position than
the vertical or overhead position. Manufacturers of electrodes usually specify a current range for each type and
size of electrode; this information is normally found on
the face of the electrode container.
Since most recommended current settings are only
approximate, final current settings and adjustments
need to be made during the welding operation. For
example, when the recommended current range for an
electrode is 90-100 amperes, the usual practice is to set
the controls midway between the two limits, or at 95
amperes. After starting the weld, make your final adjustments by either increasing or decreasing the current.
When the current is too high, the electrode melts
faster and the molten puddle will be excessively large
and irregular. High current also leaves a groove in the
base metal along both sides of the weld. This is called
undercutting, and an example is shown in figure 7-12,
view C.
With current that is too low, there is not enough heat
to melt the base metal and the molten pool will be too
small. The result is poor fusion and a irregular shaped
deposit that piles up, as shown in figure 7-12, view B.
This piling up of molten metal is called overlap. The
molten metal from the electrode lays on the work without penetrating the base metal. Both undercutting and
overlapping result in poor welds, as shown in figure
7-13.
When the electrode, current, and polarity are correct,
a good arc produces a sharp, crackling sound. When any
of these conditions are incorrect, the arc produces a
steady, hissing sound, such as steam escaping.
TAPPING method (fig. 7-11). In either method, the arc
is started by short circuiting the welding current between
the electrode and the work surface. The surge of high
current causes the end of the electrode and a small spot
on the base metal beneath the electrode to melt instantly.
In the STRIKING or BRUSHING method, the electrode
is brought down to the work with a lateral motion similar
to striking a match. As soon as the electrode touches the
work surface, it must be raised to establish the arc
(fig. 7-10). The arc length or gap between the end of the
electrode and the work should be equal to the diameter
of the electrode. When the proper arc length is obtained,
it produces a sharp, crackling sound.
In the TAPPING method, you hold the electrode in
a vertical position to the surface of the work. The arc is
started by tapping or bouncing it on the work surface
and then raising it to a distance equal to the diameter of
the electrode (fig. 7-11). When the proper length of arc
is established, a sharp, crackling sound is heard.
When the electrode is withdrawn too slowly with
either of the starting methods described above, it will
stick or freeze to the plate or base metal. If this occurs,
you can usually free the electrode by a quick sideways
wrist motion to snap the end of the electrode from the
plate. If this method fails, immediately release the electrode from the holder or shutoff the welding machine.
Use alight blow with a chipping hammer or a chisel to
free the electrode from the base metal.
CAUTION
NEVER remove your helmet or the shield
from your eyes as long as there is any possibility
that the electrode could produce an arc.
7-10
Figure 7-12.—Comparison chart of welds.
Figure 7-14.—Setting the length of an arc.
to stick frequently to the base metal, and produces
uneven deposits with irregular ripples. The recommended length of the arc is equal to the diameter of the
bare end of the electrode, as shown in figure 7-14.
The length of the arc depends upon the type of
Figure 7-13.—Undercuts and overlaps in welding.
electrode and the type of welding being done; therefore,
Length of Arc
for smaller diameter electrodes, a shorter arc is necessary than for larger electrodes. Remember: the length of
When an arc is too long, the metal melts off the
electrode in large globules and the arc may break frequently. This produces a wide, spattered, and irregular
deposit with insufficient fusion between the base metal
and the weld (fig. 7-12, view F).
When an arc is too short, it fails to generate enough
heat to melt the base metal properly, causes the electrode
the arc should be about equal to the diameter of the bare
electrode except when welding in the vertical or overhead position. In either position, a shorter arc is desirable because it gives better control of the molten puddle
and prevents atmospherical impurities from entering the
weld.
7-11
Travel Speed
Travel speed is the rate at which the electrode travels
along a weld seam. The maximum speed of welding
depends on the skill of the operator, the position of the
weld, the type of electrode, and the required joint penetration.
Normally, when the travel speed is too fast, the
molten pool cools too quickly, locking in impurities and
causing the weld bead to be narrow with pointed ripples,
as shown in figure 7-12, view D. On the other hand, if
the travel speed is too slow, the metal deposit piles up
excessively and the weld is high and wide, as shown in
figure 7-12, view E. In most cases, the limiting factor is
the highest speed that produces a satisfactory surface
appearance of a normal weld, as shown in figure 7-12,
view A.
Figure 7-15.—Work angle.
Breaking the Arc
The most commonly used method to break the arc
is to hold the electrode stationary until the crater is filled
and then slowly withdraw the electrode. This method
reduces the possibilities of crater cracks.
Reestablishing the Arc
When it becomes necessary to reestablish the arc (as
in a long weld that requires the use of more than one
electrode), the crater must first be cleaned before striking the arc. Strike the tip of the new electrode at the
forward (cold) end of the crater and establish an arc.
Move the arc backward over the crater, and then move
forward again and continue the weld. This procedure
fills the crater and prevents porosity and slag inclusions.
Figure 7-16.—Travel angle.
Peening
Peening is a procedure that involves lightly hammering a weld as it cools. This process aids in relieving
built-up stresses and preventing surface cracking in the
joint area; however, peening should be done with care
because excess hammering can work harden and increase stresses in the weld. This condition leads to weld
embrittlement and early failure. Some welds are covered by specific codes that prohibit peening so you
should check the weld specification before peening.
Electrode Angle
The angle at which you hold the electrode greatly
affects the shape of the weld bead which is very important in fillet and deep groove welding. The electrode
angle consists of two positions: work angle and travel
angle. Work angle is the angle from the horizontal
measured at right angles to the direction of welding (fig,
7-15). Travel angle is the angle in the direction of
welding and may vary from 5 to 30 degrees, depending
on the welder’s choice and conditions (fig. 7-16).
Work angle is especially important in multiple-pass
fillet welding. Normally, a small variance of the work
angle will not affect the appearance or quality of a weld;
however, when undercuts occur in the vertical section
of a fillet weld, the angle of the arc should be lowered
and the electrode directed more toward the vertical
section.
ARC WELDING POSITIONS
The types of welds, joints, and welding positions
used in manual-shielded metal arc welding are very
similar to those used in oxygas welding. Naturally, the
techniques are somewhat different because of the equipment involved is different.
7-12
Figure 7-17.—Butt joints in the flat position.
FLAT-POSITION WELDING
can be made on just about any type of joint providing
you can rotate the section you are welding on to the
appropriate position. Techniques that are useful in making butt joints in the flat position, with and without the
use of backing strips, are described below.
Earlier reexplained that welding can be done in
any position, but it is much simpler when done in the
flat position. In this position, the work is less tiring,
welding speed is faster, the molten puddle is not as likely
to run, and better penetration can be achieved. Whenever possible, try to position the work so you can weld
in the flat position. In the flat position, the face of the
weld is approximately horizontal.
BUTT JOINTS WITHOUT BACKING
STRIPS.— A butt joint is used to join two plates having
surfaces in about the same plane. Several forms of butt
joints are shown in figure 7-17.
Plates up to 1/8 inch thick can be welded in one pass
with no special edge preparation. Plates from 1/8 to 3/16
inch in thickness also can be welded with no special
Joint Type
Butt joints are the primary type of joints used in the
flat position of welding; however, flat-position welding
edge preparation by welding on both sides of the joint.
7-13
Figure 7-18.—Butt welds with multipass beads.
Figure 7-20.—Undercutting in butt joint welds.
In making multipass welds, as shown in figure 7-18,
the second, third, and fourth layers of weld metal are
made with a weaving motion of the electrode. Clean
each layer of metal before laying additional beads. You
may use one of the weaving motions shown in figure
7-19, depending upon the type of joint and size of
electrode.
Figure 7-19.—Weave motions used in manual shielded arc
welding.
In the weaving motion, oscillate or move the electrode uniformly from side to side, with a slight hesitation
at the end of each oscillation. Incline the electrode 5 to
15 degrees in the direction of welding as in bead welding. When the weaving motion is not done properly,
undercutting could occur at the joint, as shown in figure
7-20. Excessive welding speed also can cause undercutting and poor fusion at the edges of the weld bead.
Tack welds should be used to keep the plates aligned for
welding. The electrode motion is the same as that used
in making a bead weld.
In welding 1/4-inch plate or heavier, you should
prepare the edges of the plates by beveling or by J-, U-,
or V-grooving, whichever is the most applicable. You
should use single or double bevels or grooves when the
specifications and/or the plate thickness requires it. The
first bead is deposited to seal the space between the two
plates and to weld the root of the joint. This bead or layer
of weld metal must be thoroughly cleaned to remove all
slag and dirt before the second layer of metal is deposited.
BUTT JOINTS WITH BACKING STRIPS.—
Welding 3/16-inch plate or thicker requires backing
strips to ensure complete fusion in the weld root pass
and to provide better control of the arc and the weld
metal. Prepare the edges of the plates in the same
manner as required for welding without backing strips.
7-14
Figure 7-22.—Horizonta1 groove weld.
Figure 7-21.—Use of backing strips in welding butt joints.
For plates up to 3/8 inch thick, the backing strips should
be approximately 1 inch wide and 3/16 inch thick. For
plates more than 1/2inch thick, the backing strips should
be 1 1/2 inches wide and 1/4 inch thick Tack-weld the
backing strip to the base of the joint, as shown in figure
7-21. The backing strip acts as a cushion for the root
pass. Complete the joint by welding additional layers of
metal. After you complete the joint, the backing strip
may be “washed” off or cut away with a cutting torch.
When specified, place a seal bead along the root of the
joint.
Figure 7-23.—Horizontal fillet weld,
HORIZONTAL-POSITION WELDING
You will discover that it is impossible to weld all
pieces in the flat position. Often the work must be done
in the horizontal position. The horizontal position has
two basic forms, depending upon whether it is used with
a groove weld or a fillet weld. In a groove weld, the axis
of the weld lies in a relative horizontal plane and the face
of the weld is in a vertical plane (fig. 7-22). In a fillet
weld, the welding is performed on the upper side of a
relatively horizontal surface and against an approximately vertical plane (fig. 7-23).
Bear in mind that many times it will not always be
possible to use a backing strip; therefore, the welder
must be able to run the root pass and get good penetration without the formation of icicles.
7-15
Figure 7-24.—Horizontal welding angles.
Figure 7-26.—Position of electrode and fusion area of fillet weld
on a tee joint.
As you move in and out of the crater, pause slightly
each time you return. This keeps the crater small and the
bead has less tendency to sag.
Joint Type
Horizontal-position welding can be used on most
types of joints. The most common types of joints it is
used on are tee joints, lap joints, and butt joints.
Figure 7-25.—Tack-weld to hold the tee joint elements in place.
TEE JOINTS.— When you make tee joints in the
horizontal position, the two plates are at right angles to
each other in the form of an inverted T. The edge of the
vertical plate may be tack-welded to the surface of the
horizontal plate, as shown in figure 7-25.
An inexperienced welder usually finds the horizontal position of arc welding difficult, at least until he has
developed a fair degree of skill in applying the proper
technique. The primary difficulty is that in this position
you have no “shoulder” of previously deposited weld
metal to hold the molten metal.
A fillet weld is used in making the tee joint, and a
short arc is necessary to provide good fusion at the root
and along the legs of the weld (fig. 7-26, view A). Hold
the electrode at an angle of 45 degrees to the two plate
surfaces (fig. 7-26, view B) with an incline of approximately 15 degrees in the direction of welding.
When practical, weld light plates with a fillet weld
in one pass with little or no weaving of the electrode.
Welding of heavier plates may require two or more
passes in which the second pass or layer is made with a
semicircular weaving motion, as shown in figure 7-27.
To ensure good fusion and the prevention of undercutting, you should make a slight pause at the end of each
weave or oscillation.
Electrode Movement
In horizontal welding, position the electrode so that
it points upward at a 5- to 10-degree angle in conjunction
with a 20-degree travel angle (fig. 7-24). Use a narrow
weaving motion in laying the bead. This weaving motion distributes the heat evenly, reducing the tendency
of the molten puddle to sag. You should use the shortest
arc length possible, and when the force of the arc undercuts the plate at the top of the bead, lower the electrode
holder a little to increase the upward angle.
For fillet-welded tee joints on 1/2-inch plate or
heavier, deposit stringer beads in the sequence shown in
figure 7-28.
7-16
Figure 7-30.—Tack welding a lap joint.
Figure 7-27.—Weave motion for multipass fillet weld.
Figure 7-28.—Order of making string beads for a tee joint in
heavy plate.
Figure 7-31.—Position of electrode on a lap joint.
strength to that of a joint that has a fillet weld along the
entire length of one side. Intermittent welds also have
the advantage of reduced warpage and distortion.
LAP JOINTS.— When you make a lap joint, two
overlapping plates are tack-welded in place (fig. 7-30),
and a fillet weld is deposited along the joint.
The procedure for making this fillet weld is similar
to that used for making fillet welds in tee joints. You
should hold the electrode so it forms an angle of about
30 degrees from the vertical and is inclined 15 degrees
in the direction of welding. The position of the electrode
in relation to the plates is shown in figure 7-31. The
weaving motion is the same as that used for tee joints,
except that the pause at the edge of the top plate is long
enough to ensure good fusion without undercut. Lap
joints on 1/2-inch plate or heavier are made by depositing a sequence of stringer beads, as shown in figure
7-31,
Figure 7-29.—Intermittent fillet welds.
Chain-intermittent or staggered-intermittent fillet
welds, as shown in figure 7-29, are used on long tee
joints. Fillet welds of these types are for joints where
high weld strength is not required; however, the short
welds are arranged so the finished joint is equal in
In making lap joints on plates of different thickness,
you should hold the electrode so that it forms an angle
of between 20 and 30 degrees from the vertical
7-17
(fig. 7-32). Be careful not to overheat or undercut the
thinner plate edge.
BUTT JOINTS.— Most butt joints, designed for
horizontal welding, have the beveled plate positioned on
the top. The plate that is not beveled is on the bottom
and the flat edge of this plate provides a shelf for the
molten metal so that it does not run out of the joint (fig.
7-33). Often both edges are beveled to forma 60-degree
included angle. When this type of joint is used, more
skill is required because you do not have the retaining
shelf to hold the molten puddle.
Figure 7-32.—Lap joints on plates of different thickness.
The number of passes required for a joint depends
on the diameter of the electrode and the thickness of the
metal. When multiple passes are required (fig. 7-34),
place the first bead deep in the root of the joint. The
electrode holder should be inclined about 5 degrees
downward. Clean and remove all slag before applying
each following bead. The second bead should be placed
with the electrode holder held about 10 degrees upward.
For the third pass, hold the electrode holder 10 to 15
degrees downward from the horizontal. Use a slight
weaving motion and ensure that each bead penetrates
the base metal.
VERTICAL-POSITION WELDING
A “vertical weld” is defined as a weld that is applied
to a vertical surface or one that is inclined 45 degrees or
less (fig. 7-35). Erecting structures, such as buildings,
pontoons, tanks, and pipelines, require welding in this
position. Welding on a vertical surface is much more
difficult than welding in the flat or horizontal position
due to the force of gravity. Gravity pulls the molten
metal down. To counteract this force, you should use
fast-freeze or fill-freeze electrodes.
Figure 7-33.—Horizontal butt joint.
Vertical welding is done in either an upward or
downward position. The terms used for the direction of
welding are vertical up or vertical down. Vertical down
welding is suited for welding light gauge metal because
the penetration is shallow and diminishes the possibility
of burning through the metal. Furthermore, vertical
down welding is faster which is very important in production work.
Figure 7-34.—Multiple passes.
Current Settings and Electrode Movement
In vertical arc welding, the current settings should
be less than those used for the same electrode in the flat
position. Another difference is that the current used for
welding upward on a vertical plate is slightly higher than
the current used for welding downward on the same
plate.
Figure 7-35.—Vertical weld plate positions.
7-18
Figure 7-36.—Bead welding in the vertical position.
To produce good welds, you must maintain the
proper angle between the electrode and the base metal.
In welding upward, you should hold the electrode at 90
degrees to the vertical, as shown in figure 7-36, view A.
When weaving is necessary, oscillate the electrode, as
shown in figure 7-36, view B.
In vertical down welding, incline the outer end of
the electrode downward about 15 degrees from the
horizontal while keeping the arc pointing upward toward the deposited molten metal (figure 7-36, view C).
When vertical down welding requires a weave bead, you
should oscillate the electrode, as shown in figure 7-36,
view D.
Joint Type
Vertical welding is used on most types of joints. The
types of joints you will most often use it on are tee joints,
lap joints, and butt joints.
When making fillet welds in either tee or lap joints
in the vertical position, hold the electrode at 90 degrees
to the plates or not more than 15 degrees off the horizontal for proper molten metal control. Keep the arc
short to obtain good fusion and penetration.
TEE JOINTS.— To weld tee joints in the vertical
position, start the joint at the bottom and weld upward.
7-19
Figure 7-37.—Fillet welds in the vertical position.
Move the electrode in a triangular weaving motion, as
shown in figure 7-37, view A. A slight pause in the
weave, at the points indicated, improves the sidewall
penetration and provides good fusion at the root of the
joint.
When more than one pass is necessary to make a tee
weld, you may use either of the weaving motions shown
in figure 7-37, views C and D. A slight pause at the end
of the weave will ensure fusion without undercutting the
edges of the plates.
When the weld metal overheats, you should quickly
shift the electrode away from the crater without breaking the arc, as shown in figure 7-37, view B. This permits
the molten metal to solidify without running downward.
Return the electrode immediately to the crater of the
weld in order to maintain the desired size of the weld.
LAP JOINTS.— To make welds on lap joints in the
vertical position, you should move the electrode in a
triangular weaving motion, as shown in figure 7-37,
view E. Use the same procedure, as outlined above for
the tee joint, except direct the electrode more toward the
vertical plate marked “G.” Hold the arc short, and pause
7-20
with no undercutting. Welds made on plates with a
backup strip should be done in the same manner.
E-7018 Electrode Welding Technique
The previously described vertical welding techniques generally cover all types of electrodes; however,
you should modify the procedure slightly when using
E-7018 electrodes.
When vertical down welding, you should drag the
electrode lightly using a very short arc. Refrain from
using a long arc since the weld depends on the molten
slag for shielding. Small weaves and stringer beads are
preferred to wide weave passes. Use higher amperage
with ac than with dc. Point the electrode straight into the
joint and tip it forward only a few degrees in the direction of travel.
On vertical up welding, a triangular weave motion
produces the best results. Do not use a whipping motion
or remove the electrode from the molten puddle. Point
the electrode straight into the joint and slightly upward
in order to allow the arc force to help control the puddle.
Adjust the amperage in the lower level of the recommended range.
Figure 7-38.—Butt joint welding in the vertical position.
OVERHEAD-POSITION WELDING
Overhead welding is the most difficult position in
welding. Not only do you have to contend with the force
of gravity but the majority of the time you also have to
assume an awkward stance. Nevertheless, with practice
it is possible to make welds equal to those made in the
other positions.
slightly at the surface of plate G. Try not to undercut
either of the plates or to allow the molten metal to
overlap at the edges of the weave.
Lap joints on heavier plate may require more than
one bead. If it does, clean the initial bead thoroughly and
place all subsequent beads as shown in figure 7-37, view
F. The precautions to ensure good fusion and uniform
weld deposits that was previously outlined for tee joints
also apply to lap joints.
Current Settings and Electrode Movement
To retain complete control of the molten puddle, use
a very short arc and reduce the amperage as recommended. As in the vertical position of welding, gravity
causes the molten metal to drop or sag from the plate.
When too long an arc is held, the transfer of metal from
the electrode to the base metal becomes increasingly
difficult, and the chances of large globules of molten
metal dropping from the electrode increase. When you
routinely shorten and lengthen the arc, the dropping of
molten metal can be prevented; however, you will defeat
your purpose should you carry too large a pool of molten
metal in the weld.
BUTT JOINTS.— Prepare the plates used in vertical welding identically to those prepared for welding in
the flat position. To obtain good fusion and penetration
with no undercutting, you should hold a short arc and
the motion of the arc should be carefully controlled.
Butt joints on beveled plates 1/4 inch thick can be
welded in one pass by using a triangular weave motion,
as shown in figure 7-38, view A.
Welds made on 1/2-inch plate or heavier should be
done in several passes, as shown in figure 7-38, view B.
Deposit the last pass with a semicircular weaving motion with a slight “whip-up” and pause of the electrode
at the edge of the bead. This produces a good cover pass
One of the problems encountered in overhead welding is the weight of the cable. To reduce arm and wrist
fatigue, drape the cable over your shoulder when welding in the standing position. When sitting, place the
7-21
cable over your knee. With experience, cable placement
will become second nature.
WARNING
Because of the possibility of falling molten
metal, use a protective garment that has a tight
fitting collar that buttons or zips up to the neck.
Roll down your sleeves and wear a cap and
appropriate shoes.
Type of Welds
Techniques used in making bead welds, butt joints,
and fillet welds in the overhead position are discussed
in the following paragraphs.
BEAD WELDS.— For bead welds, the work angle
of the electrode is 90 degrees to the base metal (fig. 7-39,
view A). The travel angle should be 10 to 15 degrees in
the direction of welding (fig. 7-39, view B).
Figure 7-39.—Position of electrode and weave motion in the
overhead position.
Weave beads can be made by using the motion
shown in figure 7-39, view C. A rather rapid motion is
necessary at the end of each semicircular weave to
control the molten metal deposit. Avoid excessive weaving because this can cause overheating of the weld
deposit and the formation of a large, uncontrollable
pool.
BUTT JOINTS.— Prepare the plates for overhead
butt welding in the same manner as required for the flat
position. The best results are obtained when backing
strips are used; however, you must remember that you
will not always be able to use a backing strip. When you
bevel the plates with a featheredge and do not use a
backing strip, the weld will repeatedly burn through
unless extreme care is taken by the operator.
For overhead butt welding, bead welds are preferred
over weave welds. Clean each bead and chip out the
rough areas before placing the next pass. The electrode
position and the order of deposition of the weld beads
when welding on 1/4- or 1/2-inch plate are shown in
figure 7-40, views B and C. Make the first pass with the
electrode held at 90 degrees to the plate, as shown in
figure 7-40, view A. When you use an electrode that is
too large, you can not hold a short arc in the root area.
This results in insufficient root penetration and inferior
joints.
FILLET WELDS.— In making fillet welds in
either tee or lap joints in the overhead position, maintain
a short arc and refrain from weaving of the electrode.
Figure 7-40.—Multipass butt joint in the overhead position.
7-22
Figure 7-41.—Fillet welding in the overhead position.
the arc and allow the metal to solidify. Immediately
return the electrode to the crater and continue welding.
Overhead fillet welds for either tee or lap joints on
heavy plate require several passes or beads to complete
the joint. One example of an order of bead deposition is
shown in figure 7-41, view A. The root pass is a string
bead made with no weaving motion of the electrode. Tilt
the electrode about 15 degrees in the direction of
welding, as shown in figure 7-41, view C, and with a
Hold the electrode at approximately 30 degrees to the
vertical plate and move it uniformly in the direction of
welding, as shown in figure 7-41, view B. Control the
arc motion to secure good penetration in the root of the
weld and good fusion with the sidewalls of the vertical
and horizontal plates. When the molten metal becomes
too fluid and tends to sag, whip the electrode quickly
away from the crater and ahead of the weld to lengthen
7-23
Table 7-3—Causes and Cures of Common Welding Problems
7-24
the root gap to maintain the strength requirement. In
some cases, it is advantageous to make a groove weld l
to avoid extremely large fillet welds.
slight circular motion make the second, third, and fourth
passes. This motion of the electrode permits greater
control and better distribution of the weld metal.
Remove all slag and oxides from the surface of each pass
by chipping or wire brushing before applying additional
beads to the joint.
13. Inspect your work after completion and
immediately remove and replace any defective weld.
14. Observe the size requirement for each weld and
make sure that you meet or slightly exceed the specified
size.
WELDING DIFFICULTIES
Many of the welding difficulties in metal-arc welding are the same as in oxygas welding. A few such
problems include undercut, cracked welds, poor fusion,
and incomplete penetration.
15. Make sure that the finished appearance of the
weld is smooth and that overlaps and undercuts have
been repaired.
Table 7-3 provides an illustration of the most common welding problems encountered during the arcwelding process and methods to correct them.
PIPE WELDING
Welding is the simplest and easiest way to join
sections of pipe. The need for complicated joint designs
and special threading equipment is eliminated. Welded
pipe has reduced flow restrictions compared to mechanical connections and the overall installation costs
are less. The most popular method for welding pipe is
the shielded metal-arc process; however, gas shielded
arc methods have made big inroads as a result of new
advances in welding technology.
Every welder has the responsibility of making each
weld the best one possible. You can produce quality
welds by adhering to the rules that follow.
1. Use only high-quality welding machines,
electrodes, and welding accessories.
2. Know the base material that you are working
on.
Pipe welding has become recognized as a profession in itself. Even though many of the skills are comparable to other types of welding, pipe welders develop
skills that are unique only to pipe welding. Because of
the hazardous materials that most pipelines carry, pipe
welders are required to pass specific tests before they
can be certified
3. Select the proper welding process that gives the
highest quality welds for the base material used.
4. Select the proper welding procedure that meets
the service requirement of the finished weldment.
5. Select the correct electrode for the job in
question.
In the following paragraphs, pipe welding positions,
pipe welding procedures, definitions, and related information are discussed.
6. When preheating is specified or required make
sure you meet the temperature requirements. In any
case, do not weld on material that is below 32°F without
first preheating.
PIPE WELDING POSITIONS
7. Clean the base metal of all slag, paint, grease,
oil, moisture, or any other foreign materials.
You may recall from chapter 3 of this manual that
there are four positions used in pipe welding (fig. 3-30).
They are known as the horizontal rolled position (1G),
the horizontal fixed position (5G), pipe inclined fixed
(6G), and the vertical position (2G). Remember: these
terms refer to the position of the pipe and not to the weld
8. Remove weld slag and thoroughly clean each
bead before making the next bead or pass.
9. Do not weld over cracks or porous tack welds.
Remove defective tack welds before welding.
PIPE WELDING PROCEDURES
10. Be particularly alert to obtain root fusion on the
first pass of fillet and groove welds.
Welds that you cannot make in a single pass should
be made in interlocked multiple layers, not less than one
layer for each 1/8 inch of pipe thickness. Deposit each
layer with a weaving or oscillating motion. To prevent
entrapping slag in the weld metal, you should clean each
layer thoroughly before depositing the next layer.
11. When groove weld root gaps are excessive,
build up one side of the joint before welding the pieces
together.
12. When fillet weld root gaps are excessive, be
sure you increase the size of the fillet weld to the size of
7-25
Figure 7-43.—Flange connections.
Figure 7-42.—Butt joints and socket fitting joints.
Butt joints are commonly used between pipes and
between pipes and welded fittings. They are also used
for butt welding of flanges and welding stubs. In making
a butt joint, place two pieces of pipe end to end, align
them, and then weld them. (See fig. 7-42.)
When the wall thickness of the pipe is 3/4 inch or
less, you can use either the single V or single U type of
Figure 7-44.—Flange alignment.
JOINT PREPARATION AND FIT-UP
butt joint; however, when the wall thickness is more than
3/4 inch, only the single U type should be used.
Fillet welds are used for welding slip-on and
You must carefully prepare pipe joints for welding
if you want good results. Clean the weld edges or
surfaces of all loose scale, slag, rust, paint, oil, and other
foreign matter. Ensure that the joint surfaces are smooth
and uniform. Remove the slag from flame-cut edges;
however, it is not necessary to remove the temper color.
When you prepare joints for welding, remember
that bevels must be cut accurately. Bevels can be made
by machining, grinding, or using a gas cutting torch. In
fieldwork, the welding operator usually must make the
bevel cuts with a gas torch. When you are beveling, cut
away as little metal as possible to allow for complete
fusion and penetration. Proper beveling reduces the
amount of filler metal required which, in turn, reduces
time and expense. In addition, it also means less strain
in the weld and a better job of design and welding.
threaded flanges to pipe. Depending on the flange and
type of service, fillet welds may be required on both
sides of the flange or in combination with a bevel weld
(fig. 7-43). Fillet welds are also used in welding screw
or socket couplings to pipe, using a single fillet weld
(fig. 7-42). Sometimes flanges require alignment. Figure 7-44 shows one type of flange square and its use in
vertical and horizontal alignment.
Another form of fillet weld used in pipe fitting is a
seal weld A seal weld is used primarily to obtain tightness and prevent leakage. Seal welds should not be
considered as adding strength to the joint.
7-26
yet not exceeding 3/16 inch, that ensures complete
fusion and penetration without undercutting and slag
inclusions.
Make certain the welding current is within the range
recommended by the manufacturers of the welding
machines and electrodes.
WEATHER CONDITIONS
Do not assign a welder to a job under any of the
following conditions listed below unless the welder and
the work area are properly protected:
c When the atmospheric temperature is less than
0°F
Figure 7-45.—Angle iron jig.
Align the piping before welding and maintain it in
alignment during the welding operation. The maximum
alignment tolerance is 20 percent of the pipe thickness.
To ensure proper initial alignment, you should use
clamps or jigs as holding devices. Apiece of angle iron
makes a good jig for a small-diameter pipe (fig. 7-45),
while a section of channel or I-beam is more suitable for
larger diameter pipe.
l When the surfaces are wet
l When rain or snow is falling, or moisture is
condensing on the weld surfaces
l During periods of high wind
At temperatures between 0°F and 32°F, heat the
weld area within 3 inches of the joint with a torch to a
temperature warm to the hand before beginning to weld.
TACK WELDING
When welding material solidly, you may use tack
welds to hold it in place temporarily. Tack welding is
one of the most important steps in pipe welding or any
other type of welding. The number of tack welds required depends upon the diameter of the pipe. For
1/2-inch pipe, you need two tacks; place them directly
opposite each other. As a rule, four tacks are adequate
for standard size of pipe. The size of a tack weld is
determined by the wall thickness of the pipe. Be sure
that a tack weld is not more than twice the pipe thickness
in length or two thirds of the pipe thickness in depth.
Tack welds should be the same quality as the final weld.
Ensure that the tack welds have good fusion and are
thoroughly cleaned before proceeding with the weld.
WEARFACING
The Seabee welder can greatly extend the life of
construction equipment by the use of wearfacing procedures. Wearfacing is the process of applying a layer of
special composition metal onto the surface of another
type of metal for the purpose of reducing wear. The
selection of a wearfacing alloy for application is based
on the ability of the alloy to withstand impact or abrasion. Impact refers to a blow or series of blows to a
surface that results in fracture or gradual deterioration.
Abrasion is the grinding action that results when one
surface slides, rolls, or rubs against another. Under
high-compressive loads, this action can result in gouging.
Alloys that are abrasion resistant are poor in withstanding impact. Conversely, those that withstand impact well are poor in resisting abrasion; however, there
are many alloys whose wearfacing properties fall between the two extremes. These alloys offer some protection against abrasion and withstand impact well.
SPACERS
In addition to tack welds, spacers sometimes are
required to maintain proper joint alignment. Spacers are
accurately machined pieces of metal that conform to the
dimensions of the joint design used. Spacers are sometimes referred to as chill rings or backing rings, and they
serve a number of purposes. They provide a means for
maintaining the specified root opening, provide a convenient location for tack welds, and aid in the pipe
alignment. In addition, spacers can prevent weld spatter
and the formation of slag or icicles inside the pipe.
WORKPIECE PREPARATION
Before you wear-face a workpiece, all dirt, oil, rust,
grease, and other foreign matter must be removed. If you
do not, your finished product will be porous and subject
to spalling. You also need a solid foundation; therefore,
repair all cracks and remove any metal that is fatigued
or rolled over.
ELECTRODE SELECTION
Select the electrode that is best suited for the position and type of welding to be done. For the root pass of
a multilayer weld, you need an electrode large enough,
7-27
TECHNIQUES
Where possible, position the workpiece for downhand welding. This allows you to finish the job quicker
and at less cost.
The building up and wearfacing of cast iron is not
generally recommended because cast iron tends to
crack. However, some cast-iron parts that are subject to
straight abrasion can be wearfaced successfully. You
must preheat these parts to temperatures of 1000°F to
1200°F and then allow them to cool slowly after wearfacing. Peening deposits on cast iron helps to relieve
stresses after welding.
Welding materials for building up worn parts differ
from those used in wearfacing the same parts. Before
wearfacing a badly worn part, you must first build it up
to 3/16 to 3/8 of an inch of its finished size. The buildup
material must be compatible with both the base metal
and the wearfacing overlay as well as being strong
enough to meet the structural requirements. Also, they
must have the properties that enable them to resist cold
flowing, mushing under high-compressive loads, and
plastic deformation under heavy impact. Without these
properties, the buildup materials cannot support the
wearfacing overlay. When the overlay is not properly
supported, it will span.
Many times high-alloy wearfacing materials are
deposited on the parts before they are placed in service.
The maximum allowable wear is usually no more than
two layers deep (1/4 inch) before wearfacing. Try to
deposit the wearfacing alloy in layers that are not too
thick. Thick layers creates more problems than no overlay at all. Usually you only need two layers. The frost
layer produces an admixture with the base metal; the
second forms a wear-resistant surface.
In wearfacing built-up carbon-steel parts, maintain
high interpass temperatures and use a weaving bead,
rather than a stringer bead. (See fig. 7-46.) Limit the thickness of a single pass bead to 3/16 inch. Use the same
technique for each layer and avoid severe quenching.
Deposits made with high-alloy electrodes should
check on the surface. Checking reduces residual
Figure7-46.—Wearfacing techniques.
PREHEATING
Depending on the type of metal, sometimes it is
necessary to preheat the base metal to lessen distortion,
to prevent spalling or cracking, and to avoid thermal
shock The preheating temperature depends on the carbon and alloy content of the base metal. In general, as
carbon content increases so does the preheating temperature. Improper heating can adversely affect a metal
by reducing its resistance to wear, by making it hard and
brittle, or by making it more prone to oxidation and
scaling.
To preheat properly, you must know the composition of the base metal. A magnet can be used to determine if you are working with carbon steel or austenitic
manganese steel. Carbon steel is magnetic, but be careful because work-hardened austenitic manganese steel
is also magnetic. Make sure that you check for magnetism in a nonworked part of the austenitic manganese
steel. There are other ways to tell the difference between
metals, such as cast iron and cast steel. Cast iron chips
or cracks, while cast steel shaves. Also, some metals
give off telltale sparks when struck by a chisel.
In preheating, you should raise the surface temperature of the workpiece to the desired point and then soak
it until the heat reaches its core. After wearfacing, cool
the work places slowly.
Figure 7-47.—Comparison between cross-checking and cracking.
7-28
naturally or if it is unlikely to occur, as in large parts
where heat builds up. You can bring on checking by
sponging the deposit with a wet cloth or by spraying it
with a fine mist of water. Also you can speed up checking by occasionally striking it with a hammer while it is
cooling. When a check-free deposit is required, use a
softer alloy and adjust preheating and postheating requirements.
Figure 7-48.—Wearfacing bulldozer end bits.
Bulldozer Blades
Bulldozer blades are wear-faced by placing the end
bits in the flat position and welding beads across the
outer corners and along the edges. Be sure to preheat the
high-carbon blades before wearfacing. On worn end
bits, weld new corners and then wear-face (fig. 7-48).
Shovel teeth
Figure 7-49.—Wearfacing shovel teeth.
Wear-face shovel teeth when they are new and
before being placed into service. The weld bead pattern
used in wearfacing can have a marked effect on the
service life of the teeth. Wear-face shovel teeth that work
mainly in rock with beads running the length of each
tooth (fig. 7-49). This allows the rock to ride on the hard
metal beads. Teeth that are primarily used to work in
dirt, clay, or sand should be wear-faced with beads
running across the width of each tooth, perpendicular to
the direction of the material that flows past the teeth.
(See fig. 7-49.) This allows the material to fill the spaces
between the beads and provide more protection to the
base metal. Another effective pattern is the waffle or
crosshatch (fig. 7-50). The wearfacing is laid on the top
and sides of each tooth, 2 inches from its point. Stringer
beads behind a solid deposit reduce wash (fig. 7-51).
Figure 7-50.—Waffle or crosshatching.
(locked-in) stresses. Without checking, the combination
of residual stresses and service stresses may exceed
tensile strength and cause deep cracks or spalling (fig.
7-47). Be sure to induce checking if it does not occur
Figure 7-51.—Comparison of wearfacing patterns for shovel teeth.
7-29
Table 7-4.—Table of Recommended Electrode Sizes, Current Settings, and Cutting Speeds for Carbon-Arc Cutting Different Thicknesses
of Steel Plate
More information on wearfacing applications may
be obtained from the NCF Welding Materials Handbook, NAVFAC P-433.
The carbon-arc method of cutting is successful on
cast iron because the arc temperature is high enough to
melt the oxides formed. It is especially important to
undercut the cast-iron kerf to produce an even cut.
Position the electrode so the molten metal flows away
from the gouge or cutting areas. Table 7-4 is a list of
cutting speeds, plate thicknesses, and current settings
for carbon-arc cutting.
CARBON-ARC CUTTING
Metals can be cut cleanly with a carbon electrode
arc because no foreign metals are introduced at the arc.
The cutting current should be 25 to 50 amps above the
welding current for the same thickness of metal.
Because of the high currents required, the graphite
form of carbon electrode is better. To reduce the heating
effect on the electrode, you should not let it extend more
than 6 inches beyond the holder when cutting. If the
carbon burns away too fast, shorten the length that it
extends out of the electrode holder to as little as 3 inches.
Operating a carbon electrode at extremely high temperatures causes its surface to oxidize and burn away, resulting in a rapid reduction in the electrode diameter.
The carbon electrode point should be ground so that
it is very sharp. During the actual cutting, move the
carbon electrode in a vertical elliptical movement to
undercut the metal; this aids in the removal of the molten
metal. As in oxygen cutting, a crescent motion is preferred. Figure 7-52 shows the relative positions of the
electrode and the work in the cutting of cast iron.
Carbon-arc cutting does not require special generators. Standard arc-welding generators and other items
of arc-welding station equipment are suitable for use.
Straight polarity direct current (DCSP) is always used.
Because of the high temperature and the intensity
of the arc, choose a shade of helmet lens that is darker
than the normal shade you would use for welding on the
same thickness of metal. A number 12 or 14 lens shade
is recommended for carbon-arc welding or cutting.
AIR CARBON-ARC CUTTING
Air carbon-arc cutting (ACC) is a process of cutting,
piercing, or gouging metal by heating it to a molten state
and then using compressed air to blow away the molten
Figure 7-52.—Carbon-arc cutting on cast iron.
7-30
welding. The electrode holder operates at air pressures
varying between 60 and 100 psig.
During use, bare carbon or graphite electrodes become smaller due to oxidation caused by heat buildup.
Copper coating these electrodes reduces the heat
buildup and prolong their use.
The operating procedures for air carbon-arc cutting
and gouging are basically the same. The procedures are
as follows:
l Adjust the machine to the correct current for
electrode diameter.
l Start the air compressor and adjust the regulator
to the correct air pressure. Use the lowest air
pressure possible-just enough pressure to blow
away the molten metal.
l Insert the electrode in the holder. Extend the
carbon electrode 6 inches beyond the holder.
Ensure that the electrode point is properly
Figure 7-53.—Air carbon-arc cutting.
shaped.
metal. Figure 7-53 shows the process. The equipment
consists of a special holder, as shown in figure 7-54, that
l Strike the arc; then open the air-jet valve. The
air-jet disc can swivel, and the V-groove in the
disc automatically aligns the air jets along the
electrode. The electrode is adjusted relative to the
holder.
uses carbon or graphite electrodes and compressed air
fed through jets built into the electrode holder. A push
button or a hand valve on the electrode holder controls
the air jet.
l Control the arc and the speed of travel according
to the shape and the condition of the cut desired.
The air jet blows the molten metal away and usually
leaves a surface that needs no further preparation for
Figure 7-54.—Air carbon-arc electrode holder with carbon electrode installed.
7-31
Figure 7-56.—Steel electrode being used to cut plate.
Figure 7-55.—V-groove gouged in 2-inch-thick carbon steel.
METAL ELECTRODE ARC CUTTING
. Always cut away from the operator as molten
metalworking applications, such as metal shaping and
Metal can be removed with the standard electric arc,
but for good gouging or cutting results, you should use
special metal electrodes that have been designed for this
type of work, Manufacturers have developed electrodes
with special coatings that intensify the arc stream for
rapid cutting. The covering disintegrates at a slower rate
than the metallic center. This creates a deep recess that
produces a jet action that blows the molten metal away
(fig. 7-56). The main disadvantage of these electrodes
is that the additional metal produced must be removed.
other welding preparations. For gouging, hold the elec-
These electrodes are designed for cutting stainless
trode holder so the electrode slopes back from the direc-
steel, copper, aluminum, bronze, nickel, cast iron, manganese, steel, or alloy steels.
metal sprays some distance from the cutting action. You may use this process to cut or gouge
metal in the flat, horizontal, vertical, or overhead
positions.
AIR CARBON-ARC GOUGING
Air carbon-arc gouging is useful in many various
tion of travel. The air blast is directed along the electrode
toward the arc. The depth and contour of the groove are
Atypical gouge-cutting operation is shown in figure
controlled by the electrode angle and travel speed. The
7-57. Notice that the angle between the electrode and
plate is small (5 degrees or less). This makes it easy to
remove the extra metal produced by the electrode.
width of the groove is governed by the diameter of the
electrode.
When cutting or gouging a shallow groove on the
The recommended current setting is as high as the
surface of a piece of metal, you should position the
electrode will take without becoming overheated to the
point of cracking the covering. For 1/8-inch electrodes,
the setting ranges between 125 and 300 amperes; for
5/32-inch electrodes, the setting ranges between 250 and
375 amperes; and for 3/16-inch electrodes, the setting
ranges between 300 and 450 amperes. Use a very short
arc, and when cutting takes place underwater, the coating must be waterproof.
electrode holder at a very flat angle in relation to the
work. The speed of travel and the current setting also
affect the depth of the groove. The slower the movement
and the higher the current, the deeper the groove. An
example of a V-groove cut made in a 2-inch-thick mild
steel plate by a machine guided carbon-arc air-jet is
shown in figure 7-55.
7-32
Figure 7-58.—Circular magnetization (prod method).
Figure 7-57.—Gouge-cutting operation using a solid core arccutting electrode.
WELDING QUALITY CONTROL
In the fabrication or repair of equipment, tests are
used to determine the quality and soundness of the
welds. Many different tests have been designed for
specific faults. The type of test used depends upon the
requirements of the welds and the availability of testing
equipment. In this section, nondestructive and destructive testing are briefly discussed.
NONDESTRUCTIVE TESTING
Nondestructive testing is a method of testing that
does not destroy or impair the usefulness of a welded
item. These tests disclose all of the common internal and
surface defects that can occur when improper welding
procedures are used. A large choice of testing devices is
available and most of them are easier to use than the
destructive methods, especially when working on large
and expensive items.
Figure 7-59.—Longitudinal magnetization (coil method).
It is used in metals or alloys in which you can induce
magnetism. While the test piece is magnetized, a liquid
containing finely ground iron powder is applied. As long
as the magnetic field is not disturbed, the iron particles
will form a regular pattern on the surface of the test
piece. When the magnetic field is interrupted by a crack
or some other defect in the metal, the pattern of the
suspended ground metal also is interrupted. The particles of metal cluster around the defect, making it easy
to locate.
Visual Inspection
Visual inspection is usually done automatically by
the welder as he completes his welds. This is strictly a
subjective type of inspection and usually there are no
definite or rigid limits of acceptability. The welder may
use templates for weld bead contour checks. Visual
inspections are basically a comparison of finished welds
with an accepted standard. This test is effective only
when the visual qualities of a weld are the most important.
You can magnetize the test piece by either having
an electric current pass through it, as shown in figure
7-58, or by having an electric current pass through a coil
of wire that surrounds the test piece, as shown in figure
7-59. When an electric current flows in a straight line
from one contact point to the other, magnetic lines of
Magnetic Particle Inspection
Magnetic particle inspection is most effective for
the detection of surface or near surface flaws in welds.
7-33
that induces longitudinal magnetism in the part of the
workpiece that is surrounded by the coiled cable
(fig. 7-59)0
force are in a circular direction, as shown in figure 7-58.
When the current flow is through a coil around the test
piece, as shown in figure 7-59, the magnetic lines of
force are longitudinal through the test piece.
Although you can use either of these two methods,
the prod method is probably the easier to apply. Inmost
instances, it effectively serves to detect surface defects.
With the prods, however, only a small area of the test
piece can be magnetized at any one time. This magnetized area is limited to the distance between prod contact
points and a few inches on each side of the current path.
To check the entire surface, you must test each adjacent
area by changing the location of the prod contact points.
Each area of the test piece must be inspected twice—
once with the current passing through the metal in one
direction and then with the current passing through the
metal in a direction at right angles to the direction of the
first test. One of the advantages of the prod method is
that the current can be easily passed through the metal
in any desired direction. Thus, when a given area is
suspect, magnetic fields of different directions can be
induced during the test.
When a defect is to show up as a disturbance in the
pattern of the iron particles, the direction of the magnetic
field must be at right angles to the major axis of the
defect. A magnetic field having the necessary direction
is established when the current flow is parallel to the
major axis of the defect. Since the orientation of the
defect is unknown, different current directions must be
used during the test. As shown in figure 7-58, circular
magnetism is induced in the test piece so you can inspect
the piece for lengthwise cracks, while longitudinal magnetism, as shown in figure 7-59, is induced so you can
inspect the piece for transverse cracks. In general, magnetic particle inspection is satisfactory for detecting
surface cracks and subsurface cracks that are not more
than 1/4 inch below the surface.
The type of magnetic particle inspection unit commonly used in the Navy is a portable low-voltage unit
having a maximum magnetizing output of 1,000 amperes, either alternating or direct current. It is ready to
operate when plugged into the voltage supply specified
by the manufacturer. The unit consists of a magnetizing
current source, controls, metering, three 10-foot lengths
of flexible cable, and a prod kit. The prod kit includes
an insulated prod grip fitted with an ON-OFF relay or
current control switch, a pair of heavy copper contact
prods, and two 5-foot lengths of flexible cable. Cable
fittings are designed so that either end of the cable can
be connected to the unit, to the prods, or to any other
cable. The three outlets on the front of the unit make
changing from alternating to direct current or vice versa
very easy. The outlets are labeled as follows: left is ac,
the center is COMMON, and the right is dc. One cable
will always be plugged into the COMMON outlet,
while the other cable is plugged into either the ac or dc
outlet, depending upon what type of current the test
requires. For most work, alternating current magnetization effectively locates fatigue cracks and similar defects extending through to the surface. When you
require a more sensitive inspection to detect defects
below the surface, use direct current.
The prod method is accomplished by adjusting the
unit for a current output suitable for the magnetizing and
testing of any particular kind of metal. The current
setting required depends on the distance between prod
contact points. With the prod kit that is supplied with the
unit, the space between prod contact points is 4 to 6
inches. A current setting between 300 and 400 amperes
is satisfactory when the material thickness is less than
3/4 inch. When the material thickness is over 3/4 inch,
use 400 to 600 amperes. When the prod contact points
are closer together, the same magnetic field force can be
obtained with less current. With prods constantly at the
same spacing, more current will induce a greater field
strength.
After adjusting the unit, place the prods in position.
Hold them infirm contact with the metal and turn on the
current. Then apply magnetic particles to the test area
with the duster bulb and look for any indicator patterns.
With the current still on, remove the excess particles
from the test area with a blower bulb and complete the
inspection. Do not move the prods until after the current
has been turned off. To do so could cause the current to
arc, resulting in a flash similar to that occurring in arc
welding.
You can use the unit with alternating or direct
current in either of two ways: (1) with prods attached to
the flexible cable and used as contacts for the current to
pass into and out of a portion of the test piece, setting
up circular magnetization in the area between the prods
contact points, as shown in figure 7-58; or (2) with the
flexible cable wrapped around the work to form a coil
When you use magnetic particle inspection, hairline
cracks that are otherwise invisible are readily indicated
by an unmistakable outline of the defect. Large voids
beneath the surface are easier to detect than small voids,
but any defect below the surface is more difficult to
detect than one that extends through to the surface. Since
7-34
alternating current. Set the current regulator to deliver a
current identical to that used for the inspection and turn
on the unit. Gradually decrease the current until the
ammeter indicates zero. On large pieces, it may be
necessary to demagnetize a small portion of the work at
a time.
false indications frequently occur, you must be able to
interpret the particle indications accurately.
The factors that help you interpret the test results
include the amount of magnetizing current applied, the
shape of the indication, the sharpness of the outline, the
width of the pattern, and the height or buildup of the
particles. Although these characteristics do not determine the seriousness of the fault, they do serve to
identify the kind of defect.
A check for the presence of a magnetic field may be
made by using a small compass. A deviation of the
needle from the normal position, when the compass is
held near the workpiece, is an indication that a magnetic
field is present. Also you can use an instrument called a
field indicator to check for the presence of a magnetic
field. This instrument usually comes with the magnetic
particle inspection unite
The indication of a crack is a sharp, well-defined
pattern of magnetic particles having a definite buildup.
This indication is produced by a relatively low-magnetizing current. Seams are revealed by a straight, sharp,
fine indication. The buildup of particles is relatively
weak, and the magnetizing current must be higher than
that required to detect cracks. Small porosity and
rounded indentations or similar defects are difficult to
detect for inexperienced inspectors. A high-magnetizing
current continuously applied is usually required. The
particle patterns for these defects are fuzzy in outline
and have a medium buildup.
Liquid Penetrant Inspection
Liquid penetrant methods are used to inspect metals
for surface defects that are similar to those revealed by
magnetic particle inspection. Unlike magnetic particle
inspection, which can reveal subsurface defects, liquid
penetrant inspection reveals only those defects that are
open to the surface.
The specifications governing the job determine
whether or not an indicated defect is to be chipped or
ground out and repaired by welding. Surface cracks are
always removed and repaired. Indications of subsurface
defects detected by magnetic particle inspection are
evaluated by the inspector. When the indication is positive, the standard policy is to grind or chip down to solid
metal and make the repair. Unless the inspector can
differentiate accurately between true and false indications, the use of magnetic particle inspection should be
restricted to the detection of surface defects, for which
this application is almost foolproof.
Four groups of liquid penetrants are presently in
use. Group I is a dye penetrant that is nonwater washable. Group II is a water washable dye penetrant. Group
III and Group IV are fluorescent penetrants. Carefully
follow the instructions given for each type of penetrant
since there are some differences in the procedures and
safety precautions required for the various penetrants.
Before using a liquid penetrant to inspect a weld,
remove all slag, rust, paint, and moisture from the
surface. Except where a specific finish is required, it is
not necessary to grind the weld surface as long as the
weld surface meets applicable specifications. Ensure the
weld contour blends into the base metal without undercutting. When a specific finish is required, perform the
liquid penetrant inspection before the finish is made.
This enables you to detect defects that extend beyond
the final dimensions, but you must make a final liquid
penetrant inspection after the specified finish has been
given.
After the indicated defects have been repaired, you
should reinspect the areas to ensure that the repair is
sound. The final step in magnetic particle inspection, is
to demagnetize the workpiece. This is especially important when the workpiece is made of high-carbon steel.
Demagnetization is essential when you use direct current to induce the magnetic field; however, it is not as
necessary when alternating current was used in the test.
In fact, the usual demagnetization procedure involves
placing the workpiece in an ac coil or solenoid and
slowly withdrawing it while current passes through the
coil.
Before using a liquid penetrant, clean the surface of
the material very carefully, including the areas next to
the inspection area. You can clean the surface by swabbing it with a clean, lint-free cloth saturated in a nonvolatile solvent or by dipping the entire piece into a
solvent. After the surface has been cleaned, remove all
traces of the cleaning material. It is extremely important
to remove all dirt, grease, scale, lint, salts, or other
Demagnetization can be accomplished with the
portable unit if a special demagnetizer is not available.
To demagnetize with the portable unit, form a coil of
flexible cable around the workpiece. Ensure that
the cable is plugged into the unit for the delivery of
7-35
Figure 7-60.—Liquid penetrant inspection.
The following actions take place when using dye
penetrants. First, the penetrant that is applied to the
surface of the material will seep into any passageway
open to the surface, as shown in figure 7-60, view A.
The penetrant is normally red in color, and like penetrating oil, it seeps into any crack or crevice that is open to
the surface. Next, the excess penetrant is removed from
the surface of the metal with the penetrant remover and
a lint-free absorbent material. Only the penetrant on top
of the metal surface is removed (fig. 7-60, view B),
leaving the penetrant that has seeped into the defect.
materials and to make sure that the surface is entirely
dry before using the liquid penetrant.
Maintain the temperature of the inspection piece
and the liquid penetrant in the range of 50°F to 100°F.
Do not attempt to use the liquid penetrant when this
temperature range cannot be maintained. Do not use an
open flame to increase the temperature because some of
the liquid penetrant materials are flammable.
After thoroughly cleaning and drying the surface,
coat the surface with the liquid penetrant. Spray or brush
on the penetrant or dip the entire piece into the penetrant.
To allow time for the penetrant to soak into all the cracks,
crevices, or other defects that are open to the surface,
keep the surface of the piece wet with the penetrant for
a minimum of 15 or 30 minutes, depending upon the
penetrant being used.
Finally, the white developer is applied to the surface
of the metal, as shown in figure 7-60, view C. The
developer is an absorbing material that actually draws
the penetrant from the defect. Therefore, the red penetrant indications in the white developer represent the
defective areas. The amount of red penetrant drawn
from the defective areas indicates the size and sometimes the type of defect. When you use dye penetrants,
the lighting in the test area must be bright enough to
enable you to see any indications of defects on the test
surface.
After keeping the surface wet with the penetrant for
the required length of time, remove any excess penetrant
from the surface with a clean, dry cloth, or absorbent
paper towel. Then dampen a clean, lint-free material
with penetrant remover and wipe the remaining excess
penetrant from the test surface. Next, allow the test
surface to dry by normal evaporation or wipe it dry with
a clean, lint-free absorbent material. In drying the surface, avoid contaminating it with oil, lint, dust, or other
materials that would interfere with the inspection.
The indications you see during a liquid penetrant
inspection must be carefully interpreted and evaluated.
In almost every inspection, some insignificant indications are present. Most of these are the result of the
failure to remove all the excess penetrant from the
surface. At least 10 percent of all indications must be
removed from the surface to determine whether defects
are actually present or whether the indications are the
result of excess penetrant. When a second inspection
does not reveal indications in the same locations, it is
usually safe to assume that the first indications were
false.
After the surface has dried, apply another substance,
called a developer. Allow the developer (powder or
liquid) to stay on the surface for a minimum of 7 minutes
before starting the inspection. Leave it on no longer than
30 minutes, thus allowing a total of 23 minutes to
evaluate the results.
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Eddy current testing operates on the principle that
whenever a coil carrying a high-frequency alternating
current is placed next to a metal, an electrical current is
produced in the metal by induction. This induced current
is called an eddy current.
Remove all penetrant inspection materials as soon
as possible after the final inspection has been made. Use
water or solvents, as appropriate. Since some of the
liquid penetrant materials are flammable, do not use
them near open flames, and do not apply them to any
surface that is at a temperature higher than 100°F. In
addition to being flammable, many solvents are poisonous in the vapor form and highly imitating to the skin in
the liquid form.
The test piece is exposed to electromagnetic energy
by being placed in or near high-frequency ac current
coils. The differences in the weld cause changes in the
impedance of the coil, and this is indicated on electronic
instruments. When there are defects, they show up as a
change in impedance, and the size of the defect is shown
by the amount of this change.
Radiographic Inspection
Radiographic inspection is a method of inspecting
weldments by the use of rays that penetrate through the
welds. X rays or gamma rays are the two types of waves
used for this process. The rays pass through the weld
and onto a sensitized film that is in direct contact with
the back of the weld. When the film is developed, gas
pockets, slag inclusions, cracks, or poor penetration will
be visible on the film.
DESTRUCTIVE TESTING
In destructive testing, sample portions of the welded
structures are required. These samples are subjected to
loads until they actually fail. The failed pieces are then
studied and compared to known standards to determine
the quality of the weld. The most common types of
destructive testing are known as free bend, guided bend,
nick-break, impact, fillet welded joint, etching, and
tensile testing. The primary disadvantage of destructive
testing is that an actual section of a weldment must be
destroyed to evaluate the weld. This type of testing is
usually used in the certification process of the welder.
Because of the danger of these rays, only qualified
personnel are authorized to perform these tests. As
Seabees, you will rarely come in contact with these
procedures.
Ultrasonic Inspection
Ultrasonic inspection of testing uses high-frequency vibrations or waves to locate and measure defects in welds. It can be used in both ferrous and
nonferrous materials. This is an extremely sensitive
system and can locate very fine surface and subsurface
cracks as well as other types of defects. All types of
joints can be tested.
Some of the testing requires elaborate equipment
that is not available for use in the field. Three tests that
may be performed in the field without elaborate equipment are the free-bend test, the guided-bend test, and the
nick-break test.
This process uses high-frequency impulses to check
the soundness of the weld. In a good weld, the signal
travels through the weld to the other side and is then
reflected back and shown on a calibrated screen. Irregularities, such as gas pockets or slag inclusions, cause the
signal to reflect back sooner and will be displayed on
the screen as a change in depth. When you use this
system, most all types of materials can be checked for
defects. Another advantage of this system is that only
one side of the weld needs to be exposed for testing.
Free-Bend Test
The FREE-BEND TEST is designed to measure the
ductility of the weld deposit and the heat-affected area
adjacent to the weld. Also it is used to determine the
percentage of elongation of the weld metal. Ductility,
you should recall, is that property of a metal that allows
it to be drawn out or hammered thin.
The first step in preparing a welded specimen for
the free-bend test is to machine the welded reinforcement crown flush with the surface of the test plate. When
the weld area of a test plate is machined, as is the case
of the guided-bend as well as in the free-bend test,
perform the machining operation in the opposite direction that the weld was deposited.
Eddy Current Testing
Eddy current is another type of testing that uses
electromagnetic energy to detect faults in weld deposits
and is effective for both ferrous and nonferrous materials. As a Seabee, you will rarely use this type of testing
in the field.
The next step in the free-bend testis to scribe two
lines on the face of the filler deposit. Locate these lines
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Figure 7-61.—Free-bend test
Figure 7-62.—Guided-bend test jig.
1/16 inch from each edge of the weld metal, as shown
in figure 7-61, view B. Measure the distance, in inches,
between the lines to the nearest 0.01 inch and let the
resulting measurement equal (x). Then bend the ends of
the test specimen until each leg forms an angle of 30
degrees to the original centerline.
With the scribed lines on the outside and the piece
placed so all the bending occurs in the weld, bend the
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Requirements for a satisfactory test area minimum
elongation of 15 percent and no cracks greater than 1/16
inch on the face of the weld.
Guided-Bend Test
Figure 7-63.—Guided-bend test specimens.
test piece by using a hydraulic press or similar machine.
When the proper precautions are taken, a blacksmith’s
forging press or hammer can be used to complete the
bending operation. If a crack more than 1/16 inch develops during the test, stop the bending because the weld
has failed; otherwise, bend the specimen flat. After
completing the test, measure the distance between the
scribed lines and call that measurement (y). The percentage of elongation is then determined by the formula:
You use the GUIDED-BEND TEST to determine
the quality of weld metal at the face and root of a welded
joint. This test is made in a specially designed jig. An
example of one type of jig is shown in figure 7-62.
The test specimen is placed across the supports of
the die. A plunger, operated from above by hydraulic
pressure, forces the specimen into the die. To fulfill the
requirements of this test, you must bend the specimen
180 degrees—the capacity of the jig. No cracks should
appear on the surface greater than 1/8 inch. The facebend tests are made in this jig with the face of the weld
in tension (outside), as shown in figure 7-63. The rootbend tests are made with the root of the weld in tension
(outside), as shown in figure 7-63.
Figure 7-64 shows a machine used for making the
guided-bend test. It is used in many welding schools and
Figure 7-64.—Testing machine for making guided-bend tests.
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which the test piece bends by the position of an auxiliary
hand that is carried along by the gauge pointer. The hand
remains at the point of maximum load after the pointer
returns to zero.
Nick-Break Test
The NICK-BREAK TEST is useful for determining
the internal quality of the weld metal. This test reveals
various internal defects (if present), such as slag inclusions, gas pockets, lack of fusion, and oxidized or
burned metal. To accomplish the nick-break test for
checking a butt weld, you must first flame-cut the test
specimens from a sample weld (fig. 7-65). Make a saw
cut at each edge through the center of the weld. The
depth of cut should be about 1/4 inch.
Next, place the saw-nicked specimen on two steel
supports, as shown in figure 7-65. Using a heave hammer, break the specimen by striking it in the zone where
you made the saw cuts. The weld metal exposed in the
break should be completely fused, free from slag inclusions, and contain no gas pockets greater than 1/16 inch
across their greatest dimension. There should not be
more than six pores or gas pockets per square inch of
exposed broken surface of the weld.
Figure 7-65.—Nick-break test of a butt weld.
testing laboratories for the daily testing of specimens.
Simple in construction and easy to use, it works by
hydraulic pressure and can apply a direct load up to
40,000 pounds, and even more on small specimens.
When you make the test, position the specimen in the
machine as previously indicated and start pumping the
actuator. Keep your eye on the large gauge and watch
the load increase. You will know the actual load under
Impact Test
You use the IMPACT TEST to check the ability
of a weld to absorb energy under impact without
Figure 7-66.—Test pieces for impact testing.
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Figure 7-67.—Performing impact test.
fracturing. This is a dynamic test in which a test specimen is broken by a single blow, and the energy used in
breaking the piece is measured in foot-pounds. This test
compares the toughness of the weld metal with the base
metal. It is useful in finding if any of the mechanical
properties of the base metal were destroyed by the
welding process.
The two kinds of specimens used for impact testing
are known as Charpy and Izod (fig. 7-66). Both test
pieces are broken in an impact testing machine. The only
difference is in the manner that they are anchored. The
Charpy piece is supported horizontally between two
anvils and the pendulum strikes opposite the notch,
as shown in figure 7-67, view A. The Izod piece is
supported as a vertical cantilever beam and is struck on
the free end projecting over the holding vise (fig. 7-67,
view B).
Fillet-Welded Joint Test
You use the FILLET-WELDED JOINT TEST to
check the soundness of a fillet weld. Soundness refers
to the degree of freedom a weld has from defects
found by visual inspection of any exposed welding
surface. These defects include penetrations, gas
pockets, and inclusions. Prepare the test specimen,
as shown in figure 7-68. Now apply force at Point A
Figure 7-68.—Test plate for fillet weld test.
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Figure 7-70.—Standard tensile test specimen.
The essential features of a tensile testing machine
are the parts that pull the test specimen and the devices
that measure the resistance of the test specimen. Another
instrument, known as an extensometer or strain gauge,
is also used to measure the strain in the test piece. Some
equipment comes with a device that records and plots
the stress-strain curve for a permanent record.
Figure 7-69.—Rupturing fillet weld test plate.
(fig. 7-69) until a break occurs in the joint. This force
may be applied by hydraulics or hammer blows.
The tensile test is classified as a destructive test
because the test specimen must be loaded or stressed
until it fails. Because of the design of the test machine,
weld samples must be machined to specific dimensions.
This explains why the test is made on a standard specimen, rather than on the part itself. It is important that the
test specimen represents the part. Not only must the
specimen be given the same heat treatment as the part
but it also must be heat-treated at the same time.
In addition to checking the fractured weld for
soundness, now is a good time to etch the weld to check
for cracks.
Etching Test
The ETCHING TEST is used to determine the
soundness of a weld and also make visible the boundary
between the base metal and the weld metal.
There are many standard types of tensile test specimens, and figure 7-70 shows one standard type of specimen commonly used. The standard test piece is an
accurately machined specimen. Overall length is not a
critical item, but the diameter and gauge length are. The
0.505-inch-diameter (0.2 square inch area) cross section
of the reduced portion provides an easy factor to manipulate arithmetically. The 2-inch gauge length is the
distance between strain-measuring points. This is the
portion of the specimen where you attach the extensometer. In addition, you can use the gauge length to
determine percent elongation.
To accomplish the test, you must cut a test piece
from the welded joint so it shows a complete transverse
section of the weld. You can make the cut by either
sawing or flame cutting. File the face of the cut and then
polish it with grade 00 abrasive cloth. Now place the test
piece in the etching solution.
The etching solutions generally used are hydrochloric acid, ammonium persulfate, iodine and potassium
iodide, or nitric acid. Each solution highlights different
defects and areas of the weld. The hydrochloric acid
dissolves slag inclusions and enlarges gas pockets,
while nitric acid is used to show the refined zone as well
as the metal zone.
The tensile test amounts to applying a smooth,
steadily increasing load (or pull) on a test specimen and
measuring the resistance of the specimen until it breaks.
Even if recording equipment is not available, the testis
not difficult to perform. During the test, you observe the
behavior of the specimen and record the extensometer
and gauge readings at regular intervals. After the specimen breaks and the fracturing load is recorded, you
measure the specimen with calipers to determine the
percent of elongation and the percent reduction in area.
In addition, you should plot a stress-strain curve. From
the data obtained, you can determine tensile strength,
Tensile Strength Test
The term TENSILE STRENGTH may be defined as
the resistance to longitudinal stress or pull and is measured in pounds per square inch of cross section. Testing
for tensile strength involves placing a weld sample in a
tensile testing machine and pulling on the test sample
until it breaks.
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yield point, elastic limit, modulus of elasticity, and other
properties of the material.
l Keep welding cables dry and free of oil or grease.
Keep the cables in good condition and always take
appropriate steps to protect them from damage. When it
is necessary to run cables some distance from the machine, lay them overhead, if at all possible, using adequate support devices.
SAFETY REGULATIONS
You, as the welder, must have a thorough KNOWLEDGE of the safety precautions relating to the job. That
is not all; you should also consider it your responsibility
to observe all of the applicable safety precautions. When
welding, carelessness can cause serious injury to yourself as well as others.
Q When you are using portable machines, make
sure that the primary power cable is separate from the
welding cables so they do not become entangled. Any
portable equipment mounted on wheels should be securely blocked to prevent accidental movement during
welding operations.
Bear in mind the safety precautions for operating
welding equipment can vary considerably because of
the different types of equipment involved; therefore,
only general precautions on operating metal arc-welding equipment are presented here. For specific instructions on the operation and maintenance of your
individual equipment, consult the equipment manufacturer’s instruction manual. In regards to general precautions, know your equipment and how to operate it. Use
only approved welding equipment, and ensure that it is
maintained properly.
l When stopping work for any appreciable length
of time, be sure to de-energize the equipment. When the
equipment is not in use, you should completely disconnect it from its source of power.
. Keep the work area neat and clean. If at all
possible, make it a practice to dispose the hot electrode
stubs in a metal container.
Chapter 3 contains information on protective clothing, eye protection, and safe practices applicable to the
personal safety of the operator and other persons who
may be working nearby so that information will not be
repeated here. If necessary, go back and review the
section entitled “Safety” in chapter 3 before proceeding
to the next chapter.
l Before you start welding, ensure that the welding
machine frame is grounded, that neither terminal of the
welding generator is bonded to the frame, and that all
electrical connections are secure. The ground connection must be attached firmly to the work, not merely laid
loosely upon it.
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