Sulfide stress cracking (SSC) has been a concern for the use of high strength low alloy (HSLA) steel in oil and gas industry. A novel methodology named notch tensile slow strain rate test (NTSSRT) is used to obtain the threshold stress intensity factor KISSC to quantify SSC resistance of HSLA carbon steel. In this study we evaluate the effect of the strain rate and specimen gage diameter, on KISSC assessed by NTSSRT method. The testing is performed in environment with different H2S concentrations at pH of 3.5. At the same H2S concentration, the KISSC value decreases with a decline in strain rate due to the longer immersion time at slower strain rate. For 40%-notched specimen (notch diameter/gage diameter = 0.6), KISSC is independent on the specimen gage diameter when the gage diameter is larger than 0.125 in.
High strength low alloy (HSLA) steels are preferred for oil and gas pipelines due to their outstanding mechanical properties1,2. Sulfide stress cracking (SSC) has been a major problem for the application of HSLA carbon steel because of the wet H2S environment which commonly presents in oil and gas industry3-5. Several techniques are applied to the study of SSC of steels, including constant load test with smooth specimens and DCB testing6,7. However, the long test duration of these techniques (up to 720 hours) may lead to a change of environmental parameters during testing, which affect the reliability of the testing results. To increase the reproducibility and reliability, the notched slow strain rate testing is applied to the study of the environmentally inducted cracking (EIC) first reported by Caballero L. et.al,8. The use of notched specimens favors the localization of the environmental effect in the notch tip.
Therefore, a relationship between environmentally variable and local strain rate at the crack tip can be developed to characterize the EIC susceptibility9. However, the local strain rate in the vicinity of crack tip is difficult to determine for brittle materials or for the specimens with high susceptibility to hydrogen embrittlement. A novel notched tensile slow strain rate testing (NTSSRT) proposed by Case et. al,3,10,11 is applied to evaluate the SSC resistance of HSLA carbon steel, where hydrogen embrittlement tends to happen because of the accelerative effect of H2S on hydrogen uptake12. The threshold stress intensity factor KISSC is used in this novel NTSSRT method to evaluate the SSC resistance. Compared with the commonly used DCB method, the novel NTSSRT method is more time-effective methodology (less than 48 hours).
