Causes of Structural Heterogeneity in High-Strength OCTG Tubes and Minimizing Their Impact on Sulfide Stress Corrosion Cracking Resistance

High-strength oil country tubular goods (OCTG) like C110, according to standard API 5CT (yield strength at least 758 MPa), are subject to requirements in terms of mechanical and corrosion properties. In this work, we studied the microstructure of seamless casing tubes made of class C110 high-strength steel with a 194.5 mm diameter and 19.7 mm wall thickness, and its influence on sulfide stress corrosion cracking (SSC). Casing tubes were obtained from continuous billets by screw piercing with preliminary quenching and tempering. It was shown that cracking during the tests always begins from the inner surface of the tube. Rough segregation bands were found on the inner tube surface, which occupies about a third of the thickness of the wall. To increase the resistance of 0.3C-Cr-Mn-Mo + 0.15(V + Nb + Ti) steel to SSC, primary recommendations for adjusting the chemical composition, production technology and heat treatment were developed.

Peculiarities of Structure and Physical-Mechanical Properties of High-Strength Cr-Mo Pipe Steel Applicative Mainly in a Sour Environment

This paper demonstrates the results of the study of microstructure and physical-mechanical properties of the high-strength economically alloyed Fe-Cr-Mo steel, developed by RosNITI JSC for the production of the oil country tubular goods (OCTG) (casing and tubing). The main requirement for this steel is to provide simultaneous increased strength and resistance to sulfide stress cracking (SSC). It was shown that this problem could be solved by special heat treatment. As a result, the structure of this steel consists of a secondary sorbite with a lower dislocation density. Hardening is provided by dispersion-strengthened V, Nb carbides.

Effects of the Primary NbC Elimination on the SSCC Resistance of a HSLA Steel for Oil Country Tubular Goods

Sulfide stress corrosion cracking (SSCC) has been of particular concern in high strength low alloyed (HSLA) steels used in the oil industry, and the non-metallic inclusions are usually considered as a detrimental factor to the SSCC resistance. In the present work, continuous casting (CC) and electroslag remelting (ESR) were adopted to fabricate a 125 ksi grade steel in order to evaluate the effect of microstructure with and without primary NbC carbides (inclusions) on the SSCC resistance in the steel. It was found that ESR could remove the primary NbC carbides, and hence, slightly increase the strength without deteriorating the SSCC resistance. The elimination of primary NbC carbides caused two opposite effects on the SSCC resistance in the studied steel. On the one hand, the elimination of primary NbC carbides increased the dislocation density and the proportion of high angle boundaries (HABs), which was not good to the SSCC resistance. On the other hand, the elimination of primary NbC carbides also induced more uniform nanosized secondary NbC carbides formed during tempering, providing many irreversible hydrogen traps. These two opposite effects on SSCC resistance due to the elimination of primary NbC carbides were assumed to be offset, and thus, the SSCC resistance was not greatly improved using ESR.

Sulfide stress cracking inhibition of a supermartensitic stainless steel by using an imidazol obtained from palm oil

Purpose This paper aims to use an imidazole-based n-ionic Gemini surfactant derived from palm oil to inhibit the sulfide stress corrosion cracking of a supermartensitic stainless steel. Design/methodology/approach The slow strain rate testing technique, hydrogen permeation tests and potentiodynamic polarization curves have been used. Findings Addition of the inhibitor below the critical micelle concentration (CMC) decreased the corrosion current density (icorr), but not enough to avoid embrittlement due to the entry of hydrogen into the steel. Instead, the addition of the inhibitor close to the CMC decreased the icorr, suppressed the entry of hydrogen and inhibited the sulfide stress cracking of steel. Finally, the addition of inhibitor above the CMC led to a slight increase of icorr and promoted localized corrosion, however, the sulfide stress cracking of steel was inhibited. Originality/value A green sulfide stress corrosion cracking inhibitor of a supermartensitic stainless steel has been obtained.

Improved High-Pressure, High-Temperature (HPHT) Materials Qualification using Dissolved H₂S Concentration as the Sour Service Scalable Metric

Gas phase H<sub>2</sub>S partial pressure (P<sub>H2S</sub>) is associated with sulfide stress cracking (SSC) and is routinely used as the ‘scalable’ parameter to qualify materials for high-pressure, high-temperature (HPHT) wells. Candidate materials for HPHT wells routinely require ANSI/NACE MR0175/ISO 15156 compliance because a few mole ppm of H<sub>2</sub>S at high pressure may place the well beyond the 0.05 psia (0.3 kPa) sour service threshold. P<sub>H2S</sub> has been accepted historically as the scalable sour severity parameter. However, as the total pressure increases, the relationship between P<sub>H2S</sub> and the dissolved H<sub>2</sub>S concentration becomes non-linear. This limits the robustness of P<sub>H2S</sub> as the sour severity metric. Thus, ISO 15156-1:2020 now permits the use of H2S fugacity (f<sub>H2S</sub>), H<sub>2</sub>S activity (a<sub>H2S</sub>), and H<sub>2</sub>S aqueous concentration (C<sub>H2S</sub>) as alternatives for sour testing. This recent revision is based on evidence that f<sub>H2S</sub> and C<sub>H2S</sub> each provide better correlations to SSC at elevated total pressures than P<sub>H2S</sub>. This paper will address the merits and challenges of using f<sub>H2S</sub> or C<sub>H2S</sub> to define sour severity: We argue that C<sub>H2S</sub> is a practical, experimentally verifiable approach, which can be used to validate ionic-equation of state (EOS) frameworks used to characterize mildly sour HPHT environments.

Fit For Service Qualification for Sour Service High Strength Production Casing For High Temperature

In recent years the application of high strength carbon steel with 125ksi specified minimum yield strength as a production casing in deepwater and high-pressure reservoirs has increased. Sulfide stress cracking (SSC) can develop when high strength carbon steel is exposed to a sour environment. The H2S partial pressure in these sour reservoirs is above the 0.03 bar limit for this material at room temperature. Materials SSC performance evaluation requires an accurate simulation of field conditions in the laboratory. To evaluate the production casing SSC behavior, some fit for service (FFS) tests were carried out considering the well geothermic temperature profile for the materials selection. This paper presents a fit for service qualification carried out on Casing 125 ksi SMYS (Specified Minimum Yield Strength) materials. Two products with 125ksi SMYS were considered: one that has existed for several years and one developed more recently with a better SSC resistance – above the pH2S limit considered for the standard 125ksi SMYS material. The results obtained in this test program allowed casing 125 ksi SMYS materials selection for temperature above 65°C and environment more severe in terms of pH2S than the domain previously established for this grade. This allowed a new well production design, which saves one casing phase and avoids the necessity to use intermediate liners to prevent collapse.