Stress Corrosion Cracking of Corrosion Resistant Alloys in Halide Brines Exposed to Acidic Production Gas

API TECHNICAL REPORT 13TR1 FIRST EDITION, NOVEMBER 2017

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Contents

Page

1. Scope 1

2. Abbreviations and Symbols 1

   1. Abbreviations 1

   2. Symbols 2

3. Experimental Procedures 3

   1. General 3

   2. Alloy Groups Tested 4

   3. Brines Tested 4

4. Results 7

   1. Modified 13Cr Martensitic Stainless Steels 8

   2. Duplex and High-Ni Alloys 11

5. Other Variables 13

   1. More Severe Field Conditions 14

   2. Addition of Corrosion Inhibitor 15

   3. Presence of Titratable Oxidant 17

   4. Addition of O2 Scavenger 17

6. Discussion 17

   1. Alloy Composition and Strength 17

   2. Stress 18

   3. Brine Composition 18

   4. Test Protocols 19

   5. Test Reproducibility 19

   6. Temperature Effect 20

   7. Oxidants 20

   8. Effect of Additives 20

   9. SCC Mechanism 20

   10. Galvanic Effects 20

   11. Test Protocols 20

   12. Recommendations 21

7. Conclusions 21

Annex A (informative) Test Protocol 23

Annex B (informative) Stress vs Deflection Analysis 25

Bibliography 28

Figures

1. Crack Features of Alloy 25-32-3-125 (Test #64) 14

2. Effect of Cl and Brine Density on SCC of Modified 13Cr,  50 psi CO2,  0.4 psi H2S,  225 °F 17

1. Stress vs Deflection Analysis for the 13Cr-2Mo at 265 °F 25

2. Stress–strain Curves for the Two Mechanical Tests Performed on the 13Cr-2Mo at 265 °F 25

3. Stress vs Deflection Analysis for the 13Cr-2Mo at 350 °F 26

4. Stress–strain Curves for the Two Mechanical Tests Performed on the 13Cr-2Mo at 350 °F 26

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Contents

Tables

Page

1. API Test Protocols in Autoclave Testing in Halide Brines 3

2. Standard and Modified 13 % Chromium SSs, Duplex SSs 4

3. High Nickel SSs 5

4. Actual Mechanical Properties of Alloys Used in Testing 5

5. Brine Compositions Cited 6

6. Halide Anions Molar Concentration in Brines 7

7. API Tests of Modified 13Cr in Halide Brines + CO2 8

8. Effect of Molar Halide Concentration on SCC in 11.0 ppg Brines + CO2 on U-bends of

   Alloy 13-6-2 [10] 9

9. Additional Tests of Modified 13Cr + CO2 10

10. Tests of Modified 13Cr in Halide Brines + CO2 and H2S 10

11. Effect of O2 on SCC of Modified 13Cr Tests in 11.6 ppg CaCl2 11

12. Tests of Modified 13Cr in Aerated Bromide Brines 12

13. Aerated Brines: Effect of Brine and Temperature on SCC of 13-6-2 13

14. 90-day Tests of Modified 13Cr, N2 13

15. Tests of Duplex SS + CO2 14

16. Tests of Duplex SSs and High-Ni Alloys in 14.2 ppg CaBr2, + CO2 and H2S 15

17. Tests of Duplex SSs + Air 16

18. Tests of High-Ni Alloys at 425 °F to 450 °F 16

19. Modified 13Cr Tests of 14.2 CaBr2 + CO2 19

Introduction

A program partly sponsored by the American Petroleum Institute (API) studying the interaction of completion brines and corrosion-resistant alloys (CRAs) has been underway for several years. An earlier paper [1] addressed the effect of thiocyanate (SCN) corrosion inhibitor on promoting stress corrosion cracking (SCC) in CRAs exposed to halide brines, with a link to field failures. The current paper addresses SCC risks upon exposure of brines to an ingress of acidic production gas (CO2 or CO2 + H2S) or to air, both of which, have resulted in field failures. Test protocols are presented. Brine severity is related to halide ion concentration, including formation of complex ions with. Testing focused on a group of 13Cr martensitic stainless steels alloyed with Ni and Mo, with more limited tests of duplex stainless steels (SS) and high-Ni alloys. SCC results are presented in relation to alloy resistance and to test variables, including temperature, pH, and additives to the brine.

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Stress Corrosion Cracking of Corrosion Resistant Alloys in Halide Brines Exposed to Acidic Production Gas

1. Scope

   The annular space between the production tubing and the carbon steel casing is filled with a dense fluid, typically a halide salt. In wells with corrosion resistant alloy (CRA) tubing, SCC of the CRA tubing OD or auxiliary components has occurred in a number of wells. Halide brines have densities up to 2.2 g/ml (19.2 lb/gal or ppg) and contain a number of additives. A previous publication linked some field failures to the addition of SCN-corrosion inhibitor. [1]

   
   

   Additional field failures in CaCl2 brines have been linked to ingress of acidic gas containing CO2 and H2S and to exposure to air. SCC of martensitic stainless steel (SS), (13 % Cr, 6 % Ni, 2 % Mo) was attributed to downhole leakage of acidic gas [2], whereas SCC of a duplex SS tubing (25 % Cr, 3 % Mo) was attributed to air in the gas cap above column of brine. [3]

   
   

   To understand the effects of brine compositions on the CRAs, a joint industry project was formed under the auspices of the American Petroleum Institute (API). It has been known as the CRAs in Brine Testing Program. Under its auspices, work has been underway for a number of years on understanding the interaction of brine chemistry and CRAs.

   
   

   The current paper evaluates the SCC risks of a range of CRAs in various halide brine compositions for the case of exposure to acidic production gas (CO2+H2S). Also evaluated are SCC risks due to air exposure. However, the testing became focused on a group of martensitic stainless steels alloyed with Ni and Mo, that are collectively referred to as modified 13Cr martensitic SS, or alternatively in some publications as super (S13Cr) martensitic SSs. Most tests evaluated the as-received brine, excluding proprietary additives such as corrosion inhibitor or oxygen scavengers. For completeness and comparison, test results provided by member companies in the API program or in the publications are cited; these test protocols may be different from those in the API test protocols hence, where that occurs, significant differences are noted.

   
   

2. Abbreviations and Symbols

   1. Abbreviations

      
      

      API American Petroleum Institute

      ASTM American Society for Testing and Materials AYS actual yield stress

      BS bar stock

      CRA corrosion-resistant alloys

      HRC hardness Rockwell cone

      JIP joint industry project

      ksi 1000 pounds-force per square inch

      MSS martensitic stainless steel

      MTR material test report

      NACE National Association of Corrosion Engineers OD outside diameter

      PEEK polyetheretherketone

      PTFE polytretrafluoroethylene

      ppg pounds per gallon

      
      

      1

      2 API TECHNICAL REPORT 13TR1

      
      

      
      

      psi pound-force per square inch

      SCC stress corrosion cracking

      SCE saturated calomel electrode

      SEM scanning electron microscopy

      SS stainless steel

      SPE Society of Petroleum Engineers

      S13Cr super 13 % chromium

      UNS unified numbering system

      UTS ultimate tensile strength

      YS yield stress

      13Cr 13 % chromium

      @RT at room temperature

      @T at temperature

   2. Symbols

      
      

      3

      BrO 

      bromate ion

      CaBr2 calcium bromide

      CaCl2 calcium chloride

      CaO calcium oxide

      CO2 carbon dioxide Ca(OH)2 calcium hydroxide

      C276 chromium-nickel molybdenum alloy

      H2S hydrogen sulfide

      

      HSO3

      hydrosulfite (bisulfite) ion

      M molar concentration, expressed in moles per liter NaBr sodium bromide

      Na2CO3 sodium carbonate (soda ash) NaHCO3 sodium bicarbonate

      NaOH sodium hydroxide

      Nb niobium

      N2 nitrogen

      O2 oxygen

      PCO2 carbon dioxide pressure, expressed in pounds-force per square inch (psi). PH2S carbon dioxide pressure, expressed in pounds-force per square inch (psi). SCN thiocyanate

      ZnBr2 zinc bromide

      STRESS CORROSION CRACKING OF CORROSION RESISTANT ALLOYS IN HALIDE BRINES EXPOSED TO ACIDIC PRODUCTION GAS 3

      
      

      
      

3. Experimental Procedures

   1. General

The test results from the current API program follow a detailed protocol, outlined in Table 1.

Table 1—API Test Protocols in Autoclave Testing in Halide Brines

Stress reduction at 265 °F was about 7.5 % from that at room temperature and was approximately 11 % for tests performed at 350 °F.

The API protocol of total saturation of CO2 at PCO2 may represent a more severe test than gas leakage under field conditions. The latter case would correspond to absorption of a volume of CO2 in the annular column of brine that represents gas leakage [5, 6] rather than full saturation.

The U.S. customary unit (USC) system is used in this Technical Report. Factors hereafter permit conversions of USC units to standard international (SI) units or SI-derived units.