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.
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.
High Pressure and High Temperature wells are very critical and require special attention to avoid well integrity issues. High pressure requests the use of very high strength low alloyed steels, above 965 MPa (140 ksi), while even trace of hydrogen sulfide implies significant partial pressures of H2S, much higher than the limit of 0.05 psi (3.5 mbar) provided by NACE MR0175 / ISO 15156 standard. Consequently, and despite a high temperature that reduces the risk of cracking, it is crucial to assess the resistance to Sulfide Stress Cracking of materials. However low alloyed steels experience high corrosion rates when exposed to standardized test solutions at elevated temperatures, leading to difficulties of controlling the mechanical stress loading, with a load rising in NACE TM0177 Method A and declining in four-points bending test. In addition, close attention shall be paid to both the evolution of the mechanical properties of the materials with the temperature and the appropriate sequence of sour gas introduction with regards to the temperature control. This paper discusses the most appropriate testing protocol for overcoming these issues and provides experimental results obtained in the frame of the qualification of 965 MPa (140 ksi) controlled yield grade for HPHT applications.