User Manual - Rohrback Cosasco Systems
Contents
1. 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 sales cosasco com PN 724104 Manual Rev A WWW COSasco com 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 Chapter Chapter Chapter N Chapter Chapter 5 Chapter 6 Chapter 7 Chapter 8 DCHA Downhole Coupon Holder Assembly Table of Contents IMTFOGUGHON iccicil m 1 SOG ANON eet Types of Coupons 2 2 1 1 2 5 lilt M 7 GEI 7 Strip and Cylindrical Coupon Holder Assemblies 7 Bent Beam Coupon Holder ASSsembly i 8 Field Handling and Coupon Cleaning of Corrosion Coupons ccce 11 11 E T 50 A scenes 11 Bent Beam Coupon Holder Assembly 13 Corrosi2. 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 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 menge mI 16 Corrosion Coupon Weight Loss Measurement ae TABLE 1 GENERAL CORROSION RATE CLASSIFICATIONS Classification Expression O Poor sample shape and exposure Percent weight change time influence results Good Expressions do not give Milligrams per square decimeter per day mdd penetration rates Grams per square decimeter per day Grams per square centime
3. 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
4. bly 19 Conversion Factors and Metal Densities CHAPTE R 8 COMMON METAL ALLOYS AND THEIR DENSITIES Aluminum Alloy g cm Copper Alloys cont d g cm Ferrous Metals g cm Nickel Alloys g cm 1100 3004 Cartridge brass 260 Gray cast iron 7 20 Nickel 200 1199 5005 5357 6061 Muntz metal 280 Carbon Steel 7 86 Monel Alloy 400 6062 6070 amp 6101 Admiralty 442 443 Silicon iron Inconel Alloy 600 2024 444 amp 445 Low alloy steels Incoloy Alloy 825 2219 7178 Aluminum brass 687 Stainless steels Hastelloy B 3003 7079 Bronzes 201 202 302 304 B 5050 Aluminum bronze 5 608 304L amp 321 5052 amp 5454 Aluminum bronze 8 612 309 310 311 316 5083 5086 5154 amp Composition i 316L 317 329 amp 330 5456 Composition 7075 3 Phosphor bronze 596 510 10 524 Copper Alloys 85 5 5 5 Copper Silicon bronze 655 Brasses Copper Nickels 706 710 Durimet 20 Commercial brass 220 amp 715 Carpenter 20 Cb 3 Red Brass 230 Nickel Silver 752 20 Conversion Factors and Metal Densities is 5 ee SHORT FORM CONVERSION FORMULAS To 10 881 mpy and or mdd need 3 460 000 0 D 2 400 000 0 143 700 0 D 100 000 0 394 0 D 274 0 346 0 D 240 0 14 37 D 0 0394 D 00274 Sunes inch per gay 632 160 0 D 439 200 0 4 390 0 D 3 052 0 Centimeters per year 394 0 274 x D 27 4 x D Inches per year 1 000 0 696 0 x D Mils per year 2 x D Milligrams pe
5. eld Handling and Cleaning of DCHA Downhole Coupon Holder Assembly CHAPTER 5 Corrosion Coupons Field Handling Cleaning 1 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 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 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 Photograph coupons before and after cleaning if possible Visually examine coupons and analyze any scale or foreign materials build up on them 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 Immerse the coupon in fifteen percent 1596 inhibited hydrochloric acid for one 1 to two 2 minu
6. embly body 7 8 Installation Bent Beam Coupon Holder Assembly Components 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 Cn de i 4 Y Assembly 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 TSN DCHA Downhole Coupon Holder Assembly 9 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 10 Installation Fi
7. ensity of metal g cm x 16 4 cm in x area in 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 cm it is the same as millimeters per year or mmpy Formula 1 mmpy 87 6 x W W Weight loss in milligrams D Density of coupon in grams divided by DAT cubic centimeters g cm A Area in square centimeters cm T Time exposed in hours Formula 2 mdd Weight loss coupon g x 1000 2mg x 100 cm dm Area cm 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 18 Corrosion Coupon Weight Loss Measurement ee A ANAS A TT rr UM DCHA Downhole Coupon Holder Assem
8. finitive 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 2 Introduction Errem OR a EM S SN DCHA Downhole Coupon Holder Assembly 3 Specification CHAPTER 2 Environment Oil Gas Water Production Temperature 325 F 163 C maximum mated to DCMS Tool Pressure 10 000 psi 69 MPa maximum Body Material 316 Stainless Steel Thread Attachment 5 8 API Sucker Rod Connection Spec 11B The DCHA consists of the following components 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 10 Phillips Screwdriver 11 1 16 Hex L Key 12 5 8 Pin Sucker Rod to 5 8 Box S R Adapter o DCHA Downhole Coupon Holder Assembly 4 Specification DCHA Cutaway showing the Strip Rod and Bent Beam Coupon Holder Assemblies DCHA Downhole Coupon Holder Assembly 5 Types of Coupons CHAPTER 3 The DCHA
9. on Coupon Weight Loss Measurement 15 Conversion Factors and Metal Densities 19 ii Table of Contents esca aa Um cU M S SN 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 de
10. r square decimeter per day 1 437 D Note D is density of metal in grams per cubic centimeter g cm DCHA Downhole Coupon Holder Assembly 21 CONVERSION FACTORS To obtain Multiply By Grams per square inch per hour Milligrams per square decimeter 0 00000269 per day mdd Grams per square meter per day 22 0 0 Grams per square meter per year IJ 36 5 Inches per year 42 0 00144 D Milligrams per square decimeter per Grams per square inch per hour 372000 0 day Grams per square meter per 0 0274 year Pounds per square foot per 133 8 year Milligrams per square decimeter Ounces per square foot 3052 0 Millimeters per year Milligrams per square decimeter 0 03652 D per day mdd Grams per square meter per 0 36525 D day 2422 365 25 0 Inches per year 25 4 Ounces per square foot Milligrams per square decimeter 0 0003277 Pounds per square foot per year Milligrams per square decimeter 0 00748 per day Note D is density of metal in grams per cubic centimeter g cm D is density of metal in kilograms per cubic meter kg m
11. ressed 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 Drill diameter D through 2 holes Dimension mm in D 0 06240 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 15 Corrosion Coupon Weight Loss Measurement CHAPTER 7 Refer NACE Standard 01 69 and 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
12. ter per day Grams per square meter per hour Grams per square inch per hour Better Expressions give Inches per year ipy penetration rates Inches per month Millimeters per year mmpy Best Expresses penetration rates without Mils per year mpy Is equivalent to one decimals or large numbers thousandth of an inch per year TABLE 2 AVERAGE CORROSION RATE CLASSIFICATIONS T Average Corrosion Rate Average Pitting Rate Classification 1 0 25 12 Low Moderate 3 25 125 Severe 126 254 Very Severe 254 mils per year thousandth of an inch per year 0 001 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 17 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 cm A Area of coupon in square inches in T Time exposed in hours Formula 2 mpy Weight loss of coupon g x 1000 mils in x 365 days yr D
13. tes to remove scale or iron oxide Repeated immersion or a slightly more acidic solution may be required to clean severely coated coupons Immerse the coupon in saturated sodium bicarbonate NaHCO3 solution for one 1 minute to neutralize the acid 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 13 Bent Beam Coupon Holder Assembly CHAPTE R 6 The Bent Beam Coupon Holder Assembly is designed for testing the resistance of downhole tubing to stress corrosion cracking according to NACE TM0177 2005 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 st
14. 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 6 Types of Coupons DCHA Downhole Coupon Holder Assembly Installation CHAPTER 4 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 Strip Coupon Reference 1 Coupon Holder Body Dimensions 3 00 x 0 19 x 0 50 2 End Cap 2 Total Area 4 31 in Exposed Surface Area 3 63 in with end caps 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 ass
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