New and revised codes &

Advisory Desk/Codes & Standards
AD 364
Welding stainless steel
This Advisory Desk Note provides guidance on
welding stainless steel and gives references for
further information. Stainless steel can be readily
welded to itself, to carbon steel and to galvanized
carbon steel. In order to ensure a sound welded
joint, it is essential that the mechanical properties
and corrosion resistance of the weld and parent
material are suitably matched. Welding processes
are chosen and weld procedures developed for
the material and joint configuration to ensure that
welds can be completed without flaws and that
distortion is controlled. After welding, in order to
achieve optimum corrosion performance, crevice
features, contamination and at least all weld heat
tints deeper in colour than a pale yellow should be
removed by mechanical dressing followed by acid
pickling of the joint.
Welding processes
The most common welding process for stainless
steels is metal inert gas welding (generally referred
to as MIG). Manual metal arc welding (MMA)
and tungsten inert gas welding (TIG) require
higher levels of skill and are generally slower, so
they not preferred, except where high quality is
a requirement. Laser welding is not an option
for piecemeal fabrication but is used for factory
production runs of specific products.
More detailed information on processes
suitable for stainless steel is given at
www.bssa.org.uk.
Welding stainless steel to stainless steel
The two most common families of stainless steel
used in construction are austenitic and duplex
stainless steels, both of which are ‘weldable’.
Austenitic stainless steel is readily welded to itself
with or without filler wire. There are matching filler
metals available for most of the austenitic range
of alloys, for example grade 1.4301 (EN 10088
designation, the more common AWS designation
is type 304) is generally welded with type 19 9 L
filler metal (EN designation, as used in EN 1600,
EN 12072 and EN 12073 – the more common AWS
designation is 308L).
On the other hand, duplex stainless steel
requires more control when being welded and
may involve post weld heat treatment or special
welding consumables. In general, for welding
common grades of duplex such as grade 1.4462
(also known as grade 2205) to itself, the standard
filler specified is 22 9 3 N L (2209 in AWS).
For welding austenitic steel to duplex stainless
steel, fillers similar to those recommended below
for welding duplex stainless steel to carbon steel
should be used. It is noteworthy that austenitic
stainless steels have lower strength than duplex
grades and therefore welded joints made with
austenitic filler metals will not be as strong as the
duplex base metal.
Welding stainless steel to carbon steel
It is possible to weld stainless steel to carbon
steel, provided that an appropriate filler is
used. For welding austenitic stainless steels, the
generally accepted procedure is to use an overalloyed austenitic electrode to ensure adequate
mechanical properties and corrosion resistance.
Although a standard 19 9 L filler (AWS 308L) can
be used for joining austenitic steel to carbon steel,
more highly alloyed fillers, such as the 23 12 L
(309L) are preferable.
Similar fillers are recommended for welding
duplex stainless steels to carbon steel as for
welding duplex to duplex. Hence, as discussed
earlier, for duplex grades such as 1.4462 (2205),
the standard filler specified is 22 9 3 N L (2209
in AWS). The higher nickel content ensures the
correct 50/50 ferrite/austenite structure in the
weld deposit, thus maintaining strength, ductility
and corrosion resistance. Austenitic fillers such
as 23 12 2 L (309LMo in AWS), which are low
in carbon and have a molybdenum content
intermediate between the two steels, can also be
used.
Welding stainless steel to galvanized steel
When welding stainless steel to galvanized steel,
the zinc coating around the area to be joined must
be removed before welding. The inclusion of zinc
can result in embrittlement or reduced corrosion
resistance of the finished weld and, in addition, the
fumes given off when attempting to weld through
the galvanized layer are a significant health hazard.
Once the galvanizing has been removed, welding
requirements are as for ordinary carbon steel.
Risk of bimetallic corrosion between carbon and
stainless steel
Bimetallic corrosion between carbon and stainless
steel is rarely a problem in building environments.
However, unprotected welds between them
subject to aggressive environments such as
immersion in seawater could result in accelerated
corrosion of the less noble carbon steel. In this
instance, it is preferable to extend the coating
on the carbon steel onto the stainless steel to a
distance of about 50mm from the weld.
Further information:
Further information is available from
www.bssa.org.uk.
Design Manual for Structural Stainless Steel (Third Edition, 2006), Euro Inox and SCI. Available from www.euro-inox.org and www.steel-stainless.org/designmanual
The Online Information Centre for Stainless Steel in Construction: www.stainlessconstruction.com
EN 1011-3:2000 also provides technical recommendations for arc welding of stainless steel.
Contact: Katherine A Cashell
Tel: 01344 636525
Email: advisory@steel-sci.com
New and revised codes & standards
From BSI Updates November 2011
DRAFT BRITISH STANDARDS FOR
PUBLIC COMMENT – ADOPTIONS
11/30247279 DC
BS EN 1337-1 Structural bearings.
Part 1. General
CEN EUROPEAN STANDARDS
EN 1998-2:Eurocode 8. Design of structures for
earthquake resistance. Bridges
AMENDMENT 2: September 2011 to
EN 1998-2:2005
38
NSC
January 12
ISO PUBLICATIONS
ISO 630-1:2011
Structural steels. General technical
delivery conditions for hot-rolled
products.
Will not be implemented as a British
Standard
ISO 630-2:2011
(Edition 2)
Structural steels. Technical delivery
conditions for structural steels for
general purposes
Will not be implemented as a British
Standard
ISO 10799-1:2011
Cold-formed welded structural
hollow sections of non-alloy and
fine grain steels. Technical delivery
conditions
Will not be implemented as a British
Standard
ISO 10799-2:2011
Cold-formed welded structural
hollow sections of non-alloy and
fine grain steels. Dimensions and
sectional properties
Will not be implemented as a British
Standard
ISO 12633-1:2011
Hot-finished structural hollow
sections of non-alloy and fine grain
steels. Technical delivery conditions
Will not be implemented as a British
Standard
ISO 12633-2:2011
Hot-finished structural hollow
sections of non-alloy and fine grain
steels. Dimensions and sectional
properties
Will not be implemented as a British
Standard