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.

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.

Comparison of 2507 Duplex and 28 % Cr- Austenitic Stainless Steel Corrosion Behavior for High Pressure and High Temperature (HPHT) in Sour Service Condition with C-ring Experiment

The scarcity of oil and gas resources made High Pressure and High Temperature (HPHT) reservoir attractive to be developed. The sour service environment gives an additional factor in material selection for HPHT reservoir. Austenitic 28 Cr and super duplex stainless steel 2507 (SS 2507) are proposed to be a potential materials candidate for such conditions. C-ring tests were performed to investigate their corrosion behavior, specifically sulfide stress cracking (SSC) and sulfide stress cracking susceptibility. The C-ring tests were done under 2.55 % H2S (31.48 psia) and 50 % CO2 (617.25 psia). The testing was done in static environment conditions. Regardless of good SSC resistance for both materials, different pitting resistance is seen in both materials. The pitting resistance did not follow the general Pitting Resistance Equivalent Number (PREN), since SS 2507 super duplex (PREN > 40) has more pitting density than 28 Cr austenitic stainless steel (PREN < 40). SS 2507 super duplex pit shape tends to be larger but shallower than 28 Cr austenitic stainless steel. 28 Cr austenitic stainless steel has a smaller pit density, yet deeper and isolated.

Sulfide Stress Cracking of C-110 Steel in a Sour Environment

The scope of this study includes modeling and experimental investigation of sulfide stress cracking (SSC) of high-strength carbon steel. A model has been developed to predict hydrogen permeation in steel for a given pressure and temperature condition. The model is validated with existing and new laboratory measurements. The experiments were performed using C-110 grade steel specimens. The specimens were aged in 2% (wt.) brine saturated with mixed gas containing CH4, CO2, and H2S. The concentration H2S was maintained constant (280 ppm) while varying the partial pressure ratio of CO2 (i.e., the ratio of partial pressure of CO2 to the total pressure) from 0 to 15%. The changes occurring in the mechanical properties of the specimens were evaluated after exposure to assess material embrittlement and SSC corrosion. Besides this, the cracks developed on the surface of the specimens were examined using an optical microscope. Results show that the hydrogen permeation, and subsequently SSC resistance, of C-110 grade steel were strongly influenced by the Partial Pressure Ratio (PPR) of CO2 when the PPR was between 0 and 5%. The PPR of CO2 had a limited impact on the SSC process when it was between 10 and 15 percent.

Failure Analysis for Girth Weld of Gathering Pipelines

Through failure generalization, fracture feature analysis and material performance test, a comprehensively analysis was made on the fracture failure analysis for girth weld of gathering pipelines containing H2S gas. The results showed that the fracture failure might be mainly due to sulfide stress cracking in the girth weld. The crack originated from the fusion line on the inner surface of girth weld and extended along the girth weld to outside closed to bends. The sulfide stress cracking of the girth weld was caused by the intersection of multiple factors. The service condition was located in SSC 3 zone and the SSC risk of girth weld was high. The girth weld itself was not been stress-relieved, and its ability to resist SSC was poor. Due to low wall thickness, welding defects, welding stress and additional load, the actual stress of weld was higher.