Sulfide Stress Cracking Assessment of Carbon Steel Welding with High Content of H<SUB>2</SUB>S and CO<SUB>2</SUB>at High Temperature: A Case Study

In the oil and gas industry, it has been established that for pipelines fabricated with carbon steels, their limitation is related to H2S and CO2 environments, which is 7 to 10 psia of partial pressure of CO2. Therefore, in carbon steel cracking is shown, after 7 or 10 psia of partial pressure of CO2. The experimental work was performed under static conditions in autoclaves within a pH of 3 to 3.8;partial pressures of 16 - 96 psi for H2S and 15 - 53 psi for CO2, in the temperature range of 25°C - 150°C. It was observed that the average yielding stress used in Sulfide Stress Cracking (SSC) tests decreases with temperature increment. Hydrogen Induced Cracking (HIC) evaluations showed that X52 steel, under conditions, was not susceptible to HIC. Results of SSC did not show indications of cracking after exposure to sour solutions, except for the specimen exposed to high H2S and CO2 content (96 psi of H2S and 53 psi of CO2 of the partial pressure) and high temperature (150°C). Microcracks located between the upper and lower weld beads were also observed. However, the highest average corrosion rate was 0.27 mm/year (10.6 mpy), which occurred in samples exposed to 96 psi of H2S and 53 psi of CO2 at 150°C. Likewise, the highest localized corrosion (severe pitting attack) was obtained at the same environment with a corrosion rate of 4.2 mm/year (167 mpy). The oil and gas industry could use carbon steels pipelines in partial pressure higher than 10 psia.

Mechanism underlying formation of SSC in optical glass due to dynamic impact of single diamond scratch

During the grinding of optical glass, the abrasion directly affects the morphology and depth of subsurface cracks(SSC). The effect of dynamic impact of grinding abrasives on optical glass is an important issue in the field of optics manufacturing. In this work, a single diamond scratch was used to grind optical glass, and grinding parameters were collaboratively controlled to ensure that the cutting layer remained constant. A dynamometer was used to record the duration of the impact process, and the cross-section of the test piece was polished for scanning electron microscopy(SEM) to determine the depth of the SSCs. The experimental results show that as wheel speed increases, SSC depth tends to decrease. When the wheel speed gradually increases from 500 r/min to 2500 r/min, the probability distribution curve for the maximum SSC depth shifts downward by around 80 μm. The effect of the dynamic impact of single diamond scratch is found to be an important cause of SSC formation in optical glass during grinding, i.e., the faster the grinding, the shallower the SSCs.