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Today a need for a C125 Sulfide Stress Cracking (SSC) resistant material exists with the development of High Pressure/High Temperature (HP/HT) oil and gas fields. This paper focuses on the SS resistance of industrial heats.
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This paper discusses a study wherein the SSC resistance of 13Cr bar stock quenched and tempered to 22 HRC maximum hardness was tested and evaluated beyond the maximum H2S limit of 10 kPa (1.5 psi) established in NACE MR0175/ISO 15156-3 for use in sour service.
Martensitic Stainless Steel (SMSS) is widely used for downhole production tubing and liners in the Oil & Gas industry. Optimization of the tubular material chemistry, cleanliness and manufacturing route has delivered useful performance in H2S-containing environments (specifically SSC and stress corrosion cracking [SCC])3 resistance4,5,6. Some tubular accessories and most completion equipment require sizes not readily delivered by tubular product form. In these instances, bar stock material is a pragmatic choice.
High-strength low-alloy steel bar stocks with 110ksi (758MPa) and 125ksi (862MPa) specified minimum yield strength (SMYS) are in demand for temporary and permanent downhole tools for sour service. NACE MR0175/ISO15156 currently allows the use of low-alloy steel bar stocks without any environmental restrictions up to 22HRC, which, by most specifications, corresponds to 80ksi (552MPa) SMYS. At higher SMYS, and with exclusions of API and proprietary sour tubular grades, NACE MR0175/ISO15156 does not address solid bar stocks, a gap and opportunity addressed by this investigation. Specifically, in this paper, the sulfide-stress cracking (SSC) of commercial UNS G41xxx (41xx) alloys, including 41xxMod (i.e., carefully selected or mill modified) is investigated following a series of NACE TM0177 Method A tests in either Solution B or A (NACE Region 3). Domain diagrams for 41xx alloys are disclosed, all demonstrating that 41xx solid bar stocks are SSC resistant above 150°F (66°C) when under a new and improved specification. When SMYS is raised to 125ksi (862MPa) with 34HRC max, a safe minimum temperature of 175°F (79.5°C) is confirmed for hollow bars, well in line with current NACE MR0175/ISO15156. The metallurgical and hardness requirements of 41xx alloys are also briefly discussed, along with opportunities for further modifications of 41xx bar stocks.
In order to meet growing energy demand, oil and gas industries are facing many challenges, including the exploitation of increasingly deep fields with high pressure and high temperature in sour environments containing CO2 and H2S. Operators must carefully select materials that are resistant to these aggressive environments. The main risk associated with the use of martensitic stainless steels is the risk of sulfide stress cracking under well shut-in conditions. The aim of this study is to evaluate the performance of supermartensitic stainless steels (13Cr-5Ni- 2Mo) based on NACE TM-0177-2016 method A and alternative methods such as slow strain rate test according to TM-0198-2016 and ripple strain rate test. Cyclic potentiodynamic polarization measurements were also performed to evaluate pitting and repassivation performance. The interest of this study is to present reliable and fast criteria to predict sulfide stress cracking performance of supermartensitic stainless steels through alternative methods. The effect of buffer and chloride content on pitting resistance and sulfide stress corrosion cracking resistance will also be discussed as well as the effect of Mo and Cr on pitting resistance.
The current paper deals with a thorough analysis of these newly recognized LHZ with Scanning Electron Microscope (SEM) and Electron Back Scattering Diffraction (EBSD) investigations through the wall thickness of pipes. Internal diameter (ID) surface, intermediate zone and bulk metal microstructures showed an increase of a strong misorientation while approaching the ID. Thus, LHZ is characterized by the presence of lath and especially lower bainite type microstructures associated to high local hardness above the NACE MR 0175 / ISO 15156 limits for sour service applications.
Four-point bend testing is used extensively in the oil and gas industry to evaluate resistance of metals to sulfide stress cracking and stress corrosion cracking. The face of the specimen to be tested is stressed in tension and the reverse face in compression. The test is carried out for a specified exposure period with the specimen held under constant displacement using compact loading jigs. The compact nature of the jigs enables testing of several specimens in the test vessel simultaneously. Despite the apparent simplicity of the test, there are many factors that can influence the test results. The purpose of this standard is to establish a reliable methodology for conducting the tests to enhance repeatability and reproducibility of test data. The results of the tests can then be used with greater confidence to rank the performance of metals, the relative aggressiveness of environments, and to provide a basis for qualifying metals for service application. As such, the standard will be of particular benefit to materials and corrosion engineers in the oil and gas sector and to test laboratories providing critical data.
13Cr-5Ni-2Mo type Super Martensitic stainless steels referred to as SMSS-13Cr type grades can provide good general corrosion resistance such as in high CO2 environments combined with higher strengths and excellent toughness2 making them a prospective material choice for long term downhole completion equipment depending on actual well conditions. One of the main limiting factors for the use of SMSS-13Cr type grades is the Sulfide Stress Cracking (SSC) resistance in presence of H2S in downhole well conditions. Therefore, a good understanding of this behavior is essential to facilitate the material selection process.
Steel pipelines are sometimes subjected to demanding sour environments resulting from the presence of high H2S contents. Pipeline materials, therefore, must be resilient against sulfide stress cracking (SSC) which is caused by H2S. Beginning in the 1980s, thermo-mechanically controlled processed (TMCP) steels have been widely used for the manufacturing of large-diameter sour service pipelines. The failure of the Kashagan pipelines in 2013 raised concern regarding the use of TMCP steels in sour environments. These concerns arise from the potential for local hard zones (LHZs) to be produced on the surface of the line pipe during TMCP processes, ultimately leading to through-wall SSC failures. In the present study, several X60 - X65 TMCP steels (both with and without LHZs) have been tested under different Region 3 (R3) conditions in the NACE MR0175/ISO15156-2 pH-H2S partial pressure diagram. It can be concluded that the presence of LHZs increases TMCP steels’ sour cracking susceptibility; however, TMCP steels without LHZs pass the SSC tests at even the most severe R3 environments. Traditional HRC or HV10 testing are not able to detect LHZs, and so lower load HV 0.5 or HV 0.1 tests are necessary. For TMCP steels, the current R3 may be further divided into R3-a and R3-b sub-regions. The sour cracking severity of R3-a is less than that of R3-b. Additional actions, like enhanced mill qualification of the TMCP plate, should be considered to ensure that no LHZs exist in steels to be utilized in R3-b environments.