User Manual - Rohrback Cosasco Systems
DCHA™
DOWNHOLE COUPON HOLDER ASSEMBLY
User Manual
Rohrback Cosasco Systems, Inc.
11841 E. Smith Avenue
Santa Fe Springs, CA 90670
Tel: (562) 949-0123
(800) 635-6898
Fax: (562) 949-3065
E-mail: [email protected]
www.cosasco.com
PN: 724104-Manual Rev. A
© Rohrback Cosasco Systems, Inc.. All Rights Reserved.
DCMS™ is a trademark of Rohrback Cosasco Systems, Inc.
No part of this manual may be reproduced or transmitted in any form or by any means, electronic
or mechanical, including photocopying and recording, for any purpose, without the express written
permission of Rohrback Cosasco Systems, Inc.
DCHA™ Downhole Coupon Holder Assembly
Table of Contents
Chapter 1
Introduction..........................................................................1
Chapter 2
Specification ...........…………………………….....................3
Chapter 3
Types of Coupons ...............................................................5
Chapter 4
Installation............................................................................7
DCHA..............................................................................................7
Strip and Cylindrical Coupon Holder Assemblies............................7
Bent Beam Coupon Holder Assembly.............................................8
Chapter 5
Field Handling and Coupon Cleaning
of Corrosion Coupons.......................................................11
Field Handling.................................................................................11
Cleaning..........................................................................................11
Chapter 6
Bent-Beam Coupon Holder Assembly..............................13
Chapter 7
Corrosion Coupon Weight Loss Measurement...............15
Chapter 8
Conversion Factors and Metal Densities.........................19
i
ii
Table of Contents
DCHA™ Downhole Coupon Holder Assembly
Introduction
CHAPTER 1
The life of a production well is based on many factors. With proper monitoring
and maintenance, the integrity of the well, especially the downhole tubing is vital
for safety, environmental, and economical reasons. Production wells typically
contain water, carbon dioxide, and hydrogen sulphide. This combination of
elements along with varying temperatures, creates an extremely corrosive
environment, subjecting, the downhole tubing to corrosion damage including
metal loss, pitting, and stress corrosion cracking.
The Downhole Coupon Holder Assembly (DCHA) was developed to test the
effects of different types of corrosion on downhole tube materials, inlcuding
general corrosion, crevice corrosion, stress corrosion, and pitting in downhole
conditions.The DCHA holds up to nine coupon holders, including Bent Beam,
Strip, and Rod. The three type of coupon holders can be “mixed and matched”
according to the type of corrosion effects you are evaluating. The DCHA is
normally used conjunction with the DCMS Downhole Tool, but may also be
installed separately. If more than nine samples are required, mulitple DCHAs may
be mated together.
As with any type of corrosion detection device, coupons may not give absolute
definitive answers, but will indicate general corrosion behavior patterns and act
as a secondary metal loss measurement, when used in conjunction with the
DCMS Downhole Tool. Coupon metal loss data from the DCHA samples can
be correlated with ER probe metal loss data and temperature data, from the
Downhole tool, to effectively analyze the condition of the downhole tubing.
DCHA shown attached to the DCMS Downhole Tool
1
2
Introduction
DCHA™ Downhole Coupon Holder Assembly
CHAPTER 2
Specification
Environment:
Temperature:
Pressure:
Body Material
Thread Attachment:
Oil, Gas, Water Production
325°F (163°C) maximum (mated to DCMS Tool)
10,000 psi (69 MPa) maximum
316 Stainless Steel
5/8” API Sucker Rod Connection Spec. 11B
The DCHA consists of the following components:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
Downhole Coupon Holder Case
Downhole Coupon Holder Assembly Body
5/8” Sucker Rod Connector
Downhole Spring Carrier (2)
Downhole Tension Spring
Bull-Nose 5/8” Sucker Rod Connector
Strip Coupon Holder Assembly
Cylindrical Coupon Holder Assembly
Bent-Beam Coupon Holder Assembly
Phillips Screwdriver
1/16” Hex L-Key
5/8” Pin Sucker Rod to 5/8” Box S.R. Adapter
DCHA Downhole Coupon Holder Assembly
3
4
Specification
DCHA Cutaway showing the Strip, Rod, and Bent Beam Coupon Holder Assemblies
DCHA™ Downhole Coupon Holder Assembly
Types of Coupons
CHAPTER 3
The DCHA coupon holder assembly configuration may vary depending on what
corrosion effect you are evaluating. The DCHA can hold up to nine coupon holder
assemblies. The three types of coupons available are described below.
Strip Coupons
Strip coupons are standard metal loss coupons and are used for determining
corrosion rate and pitting in downhole environments. They are also ideal
as secondary metal loss measurement to electrical resistance probes. The
specimen is exposed to the environment in a non-stressed coupon holder. The
strip coupon holder is designed with non-metallic end caps to isolate the coupon
from the body to prevent galvanic corrosion from influencing measurement data.
Cylindrical Coupons
Cylindrical coupons are round tensile specimens to determine the extent of any
deterioration in the tensile properties of materials that have been subjected to
the downhole environment. The specimen is exposed to the environment in a
non-stressed coupon holder. The cylindrical coupon holder is designed with
non-metallic end caps to isolate the coupon from the body to prevent galvanic
corrosion from influencing measurement data.
Bent-Beam
Bent-Beam Coupons are a variant of the strip coupon, but used with an
applied stress – usually at mid-coupon, which bends the coupon. This method
is used to test for susceptibility of a material to stress corrosion cracking in
downhole environments. The bent-beam coupon holder is designed generally
in accordance with the requirements of NACE Standard TM0177-2005. A glass
bead and glass tubes are used to isolate the coupon from the body and other
metallic parts to prevent galvanic corrosion from influencing measurement data.
5
6
Types of Coupons
DCHA™ Downhole Coupon Holder Assembly
CHAPTER 4
Installation
DCHA
The DCHA comes with the individual coupon holder assemblies installed. If
coupons were included, they will be shipped separately and will need to be
mounted in the individual coupon holder assemblies.
1. Unscrew and remove one of the sucker rods from the DCHA.
2. Remove the spacer and coupon holder assemblies.
3. Assemble the coupons on the coupon holder assemblies as shown below.
Ensure that the coupons are completely insulated from mounting screws,
nuts, and coupon holders. DO NOT HANDLE COUPONS WITH BARE
HANDS! Be sure and use the proper insulation and mounting hardware when
assembling the coupons to the coupon holder assemblies.
4. Replace the coupon holder assemblies and spacer into the DCHA body and
screw the sucker rod back on.
Strip and Rod Coupon Holder Assemblies
Components:
1. Coupon Holder Body
2. End Cap (2)
1
Strip Coupon Reference:
Dimensions: 3.00” x 0.19” x 0.50”
Total Area: 4.31 in2
Exposed Surface Area: 3.63 in2
(with end caps)
2
Strip Coupon Holder
Cylindrical Coupon Holder
Assembly:
1. Remove one end from coupon assembly body.
2. Insert strip/cylindrical coupon into end cap and insert into coupon assembly
body.
7
8
Installation
Bent Beam Coupon Holder Assembly
Components:
1.
2.
3.
4.
5.
6.
7.
8.
Bent-Beam Body Coupon Holder Body (1)
Set Screw, 1/8” (1) (extras included)
Glass Beads (1) (extras included)
Screw, 4-40 x .5” (2)
Screw, 4-40 x .68” (2)
Bent Beam Guide (2)
End Cap (2)
Glass Support Tube (2)
2
3
1
6
7
5
8
4
Assembly:
1.
2.
3.
4.
5.
Glue glass bead to the inset on the 6-32 x 1/8” set screw using the adhesive included.
Remove one of the 4-40 x .68” screws and glass tube from the coupon holder body.
Insert the bent-beam coupon or specimen under the other screw with glass tube.
Re-install glass tube and screw to the coupon holder body.
Using the allen key included, install the set screw, making sure that the glass bead
is still in place. Use caution not to over tighten the set screw, install slowly to avoid
bending specimen.
DCHA™ Downhole Coupon Holder Assembly
6. Once specimen has been positioned correctly take an initial depth measurement
using a depth gauge or a vernier caliper at the center of specimen. Use the two holes
in the center of the specimen as a guide for the location of the measurement.
7. Adjust set screw very slowly using very small turn increments. After each adjustment
of the set screw measure the depth to the required dimension based on initial depth
measurement. Reference TM0177-20005 and deflect the test specimens to the
nearest 0.0025mm ( 0.00010 in.)
9
10
Installation
DCHA™ Downhole Coupon Holder Assembly
Field Handling and Cleaning of
Corrosion Coupons
CHAPTER 5
Field Handling
1. All corrosion coupons must be handled with clean gloves. NEVER HANDLE
WITH THE BARE HAND! To do so, will assuredly affect the coupon and
give false test data due to body oils, salts and other rust promoting matter
being deposited on them. Handle coupons carefully to prevent scratching or
otherwise marring the surface.
2. All corrosion coupons are weighed to 0.1 milligrams (0.0001 grams),
serialized and packaged in moisture-proof envelopes. Coupon weight sheet
data which are supplied with each order furnish the specifics of each coupon
as to material composition, weight in grams and its identifiable serial number.
3. If on-site field handling conditions prohibit the cleaning procedure described
below, the coupons should be placed in the original moisture-proof envelope
and shipped to a laboratory immediately for analysis. The corrosion coupon
should not be wiped off, coated with grease, or otherwise altered.
Cleaning
1. Photograph coupons, before and after cleaning, if possible.
2. Visually examine coupons and analyze any scale or foreign materials buildup on them.
3. Clean the coupon(s) by immersing in a suitable hydrocarbon solvent, such as
clean benzene. Do this long enough to remove any oil or paraffin deposits.
4. Immerse the coupon in fifteen percent (15%) inhibited hydrochloric acid
(HCl) for one (1) to two (2) minutes to remove scale or iron oxide. Repeated
immersion or a slightly more acidic solution may be required to clean severely
coated coupons.
5. Immerse the coupon in saturated sodium bicarbonate (NaHCO3) solution for
one (1) minute to neutralize the acid.
6. Rinse the coupon immediately in isopropyl alcohol or acetone to dry. BE
CAREFUL WITH ISOPROPYL ALCOHOL and/or ACETONE!…..they are
volatile flammable solvents.
11
12
Field Handling and Cleaning of Corrosion Coupons
7. Weigh the coupon to 0.1 milligrams (0.0001 grams). Pit depths may be
measured with a depth gauge or micrometer caliper with sharp pointed
probes. A microscope calibrated for depth measurement may also be used.
(Depth of deepest pit – in mils, inches, or micrometers – times (x) 365 and
divided by exposure time in days will give an effective calculation of pitting
rate).
8. Be sure serial numbers are matched; compare weight loss with coupon
weight sheet data for differential.
DCHA™ Downhole Coupon Holder Assembly
Bent-Beam Coupon
Holder Assembly
CHAPTER 6
The Bent Beam Coupon Holder Assembly is designed for testing the resistance
of downhole tubing to stress corrosion cracking according to NACE TM01772005 standard for “Laboratory Testing of Metals for Resistance to SSC and SCC
in H2S Environment”, Method B - NACE Standard Bent Beam Test. The method
is done by using several specimens to which each is subjected to a different
bending stress. The stressed test specimens are exposed to the environment
(in this case downhole tubing) and the failure or rate of cracking is determined.
According to the standard when testing multiple test specimens at varying
deflections, a statistically based critical factor (Sc) for a 50% probability of
failure can be obtained. The DCHA holds up to nine test fixtures, allowing for an
acceptable amount of samples to determine susceptibility to the material cracking
failure in downhole environments. Multiple DCHAs can be used if further samples
are required.
The test specimens provided by RCS are designed and machined according to
the NACE standard. Specimens not provided by RCS should be designed to the
specifications noted below.
Dimension
L
t
W
H
D
13
Size
(mm)
67.3 ±1.3
1.52 ±0.13
4.57 ±0.13
1.58 ±0.05
0.062 ±0.002
(in.)
2.65 ±0.050
0.060 ±0.0050
0.180 ±0.0050
0.062 ±0.002
0.028 ±0.0005 (No. 70 Drill)
Dimensional Drawing of the Standard Bent-Beam Test Specimen
14
Bent-Beam Coupon Holder Assembly
Cutaway of Bent Beam Coupon Holder With Coupon Installed
For further details on the standard Bent-Beam test specimens, deflection
calculations, and testing method, reference NACE Standard TM0177-2005.
DCHA™ Downhole Coupon Holder Assembly
Corrosion Coupon
Weight Loss Measurement
CHAPTER 7
(Refer NACE Standard TM-01-69 and RP-07-75):
The use of any criteria in determining corrosion rates or weight loss requires
judgment on the part of the user and should be tempered by economic
and safety requirements. Some rate expressions assume a uniform loss of
metal. Experience has shown that coupons rarely exhibit a uniform loss of
metal. Variables on the coupon surface in the form of pitting, and/or localized
concentrated corrosion along grain boundaries, or in transgranular paths usually
appear.
In determining weight loss there are a number of ways of expressing
measurements. The ultimate goal of any way of expressing weight loss
or corrosion rate is to have a readily definable and communicable way of
determining and expressing the amount of metal or alloy that has corroded
or been “eaten away” by the corrosion process.
The following are some of the commonly used methods to report or express
corrosion rate data:
1.
2.
3.
4.
5.
6.
15
General Corrosion Rate (Table 1).
Average Corrosion Rate (Table 2).
Percent Change (Table 3).
Engineering System (mils-per-year – Table 4).
Metric System (mdd or milligrams per square decimeter per day – Table 5).
Pitting Rates (Table 6).
16
Corrosion Coupon Weight Loss Measurement
TABLE 1 - GENERAL CORROSION RATE CLASSIFICATIONS
Classification
Poor (sample shape and exposure
time influence results)
Good (Expressions do not give
penetration rates)
Expression
Percent weight change
Milligrams per square decimeter per day (mdd)
Grams per square decimeter per day
Grams per square centimeter per day
Grams per square meter per hour
Grams per square inch per hour
Inches-per-year (ipy)
Inches-per-month
Millimeters-per-year (mmpy)
Mils-per-year (mpy) – Is equivalent to one
thousandth of an inch per year
Better (Expressions give
penetration rates)
Best (Expresses penetration rates without
decimals or large numbers)
Classification
Low
Moderate
Severe
Very Severe
TABLE 2 - AVERAGE CORROSION RATE CLASSIFICATIONS
Average Corrosion Rate
Average Pitting Rate
mpy
μm/a
mils/yr
μm/a
1.0
1.0 - 4.9
5.0 - 10.0
10.0 -
25
25 - 125
126 - 254
254 -
12
12 - 24
25 - 96
96 -
305
305 - 610
635 - 2438
2438 -
mpy = mils-per-year (one thousandth of an inch per year or 0.001”)
μm/a = micrometers per annum (one thousandth of a millimeter per year or
0.000001; is equivalent to 0.04 mpy)
TABLE 3 - PERCENT CHANGE
Original Value minus Final Value
Divided by
Original Value……X 100 = Percent weight change
DCHA™ Downhole Coupon Holder Assembly
TABLE 4 - ENGINEERING SYSTEM
Commonly used unit of corrosion rate expression measuring Dimensional Change or Loss of
Metal Thickness per Unit Time and referred to as mils-per-year (mpy). A mil is one
thousandth of an inch or 0.001”; if multiplied by 1000 is the same as inches-per-year or (ipy).
Formula 1: mpy = 534 x W
W = Weight loss in milligrams
DAT
D = Density of coupon in grams divided by
cubic centimeters (g/cm3)
A = Area of coupon in square inches (in2)
T = Time exposed in hours
Formula 2: mpy =
Weight loss of coupon (g) x 1000 (mils/in) x 365 (days/yr)
Density of metal (g/cm3) x 16.4 (cm3/in3) x area (in2) x days exposure
or
The weight loss of the corrosion coupon divided by the quantity of the product of the
metal density, the total exposed surface area (including sides) and the exposure time.
TABLE 5 - METRIC SYSTEM
Commonly used unit of corrosion rate expression measuring Weight Change or Weight Loss or Gain per Unit
Area per Unit Time and referred to as milligrams per square decimeter per day or “mdd”. A milligram is one
thousandth of a gram; a decimeter is 10 centimeters or almost four inches. If mdd is multiplied by 0.03652/D
(D = density in grams per cubic centimeter or g/cm3) it is the same as millimeters per year or “mmpy”.
Formula 1: mmpy = 87.6 x W
DAT
W = Weight loss in milligrams; D = Density of coupon in grams divided by
cubic centimeters (g/cm3); A = Area in square centimeters (cm2); T = Time
exposed in hours
Formula 2: mdd = Weight loss coupon (g) x 1000 (=mg) x 100 cm2 (=dm2)
Area (cm2) x exposure time in days
TABLE 6 - PITTING RATES
Pit depths may be measured with a depth gauge or micrometer caliper with sharp pointed probes. A
microscope calibrated for depth measurement may also be used. Depth of deepest pit in mils, inches or
micrometers times (x) 365 and divided by exposure time in days will give an effective calculation of pitting
rate.
17
18
Corrosion Coupon Weight Loss Measurement
DCHA™ Downhole Coupon Holder Assembly
Conversion Factors and
Metal Densities
CHAPTER 8
COMMON METAL ALLOYS AND THEIR DENSITIES
Aluminum Alloy
1100, 3004
1199, 5005, 5357, 6061,
6062, 6070, & 6101
2024
2219, 7178
3003, 7079
5050
5052 & 5454
5083, 5086, 5154, &
5456
7075
Copper Alloys
Copper
Brasses:
Commercial brass 220
Red Brass 230
g/cm
3
Copper Alloys (cont’d)
2.72 Cartridge brass 260
Muntz metal 280
2.70 Admiralty 442, 443,
2.77 444 & 445
2.81 Aluminum brass 687
2.74 Bronzes:
2.69 Aluminum bronze 5% 608
2.68 Aluminum bronze 8% 612
Composition M
2.66 Composition G
2.80 Phosphor bronze 5% 510
“
“ 10% 524
85-5-5-5
8.94 Silicon bronze 655
Copper Nickels 706, 710
8.80 & 715
8.75 Nickel Silver 752
19
g/cm3 Ferrous Metals
g/cm3
Nickel Alloys
g/cm3
8.52
8.39
7.20
7.86
7.00
7.85
Nickel 200
Monel Alloy 400
Inconel Alloy 600
Incoloy Alloy 825
Hastelloy B
“
C
“
G
8.89
8.84
8.51
8.14
9.24
8.93
8.27
Other Metals
Silver
Tantalum
Tin
Titanium
Zinc
10.49
16.60
7.30
4.54
6.52
8.52
8.33
8.16
7.78
8.45
8.77
8.86
8.77
8.80
8.52
8.94
8.75
Gray cast iron
Carbon Steel
Silicon iron
Low alloy steels
Stainless steels:
201, 202, 302, 304,
304L & 321
309, 310, 311, 316,
316L, 317, 329, & 330
347
410
430
446
502
Durimet 20
Carpenter 20 Cb 3
7.94
7.98
8.03
7.70
7.72
7.65
7.82
8.02
8.05
20 Conversion Factors and Metal Densities
SHORT FORM CONVERSION FORMULAS
To get mpy and/or mdd:
Multiply
By = mpy
By = mdd
Grams per square inch per hour 536,300.0/D*
372,000.0
“
“
“
“
day 22,270.0/D*
15,500.0
“
“
“
“
year 61.0/D*
42.5
“
“
“
“
“
“
“
“
“
centimeter per hour 3,460,000.0/D*
“
“
“ day 143,700.0/D*
“
“
“ year 394.0/D*
“
“
“
Ounces “
“
“
meter per hour 346.0/D*
“
“
day 14.37/D*
“
“ year 0.0394/D*
“
“
inch per day 632,160.0/D*
foot “
“ 4,390.0/D*
Centimeters per year
Millimeters
“ “
394.0
39.4
2,400,000.0
100,000.0
274.0
240.0
10.0
0.0274
439,200.0
3,052.0
274 x D*
27.4 x D*
Inches per year
1,000.0
696.0 x D*
Mils-per-year
------------0.696 x D*
Milligrams per square decimeter
-----------per day
1.437/D*
Note: D* is density of metal in grams per cubic centimeter-g/cm3
DCHA™ Downhole Coupon Holder Assembly
CONVERSION FACTORS
To obtain
Multiply
Grams per square inch per hour
Milligrams per square decimeter
per day (mdd)
Grams per square meter per day
“
Grams per square meter per year
“
Inches per year
“
Milligrams per square decimeter per
Grams per square inch per hour
day
“
Grams per square meter per
year
“
Pounds per square foot per
year
Milligrams per square decimeter
Ounces per square foot
Millimeters per year
Milligrams per square decimeter
per day (mdd)
“
Grams per square meter per
day
“
“
“
Inches per year
Ounces per square foot
Milligrams per square decimeter
Pounds per square foot per year
Milligrams per square decimeter
per day
Note: D* is density of metal in grams per cubic centimeter (g/cm3)
D# is density of metal in kilograms per cubic meter (kg/m3)
By
0.00000269
10.0
36.5
0.00144/D*
372000.0
0.0274
133.8
3052.0
0.03652/D*
0.36525/D*
365.25/D#
25.4
0.0003277
0.00748
21
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