Hydrogen embrittlement of high-strength API carbon steels in H2S and CO2 containing environments

Abstract

This study aims to understand the Sulfide Stress Cracking (SSC) resistance of API carbon steels exposed to wet sour environments containing CO2. A mini-pipe specimen was cut from API grade tubulars and placed in an SSC test cell to perform the investigation. The specimen was highly strained and internally pressurized while exposed to the corrosive environment for seven days. The partial pressure ratio (PPR) of CO2 (i.e. ratio of partial pressure of CO2 to the total pressure) was varied to study the effect of CO2 content on SSC. Experiments were performed while maintaining a constant H2S concentration and temperature. The steels' variations in mechanical properties (ultimate tensile strength and plastic strain before failure) after exposure to the sour environment are used to quantify the embrittlement. In addition, the specimens were examined using optical microscopes to assess the severity of the SSC corrosion based on shear deformation patterns and crack features. The SSC resistance of the tested steels was minimized when the PPR of CO2 was approximately 20%. Results demonstrate that the materials have adequate SSC corrosion resistance to be utilized in the environment containing 280 ppm H2S. Nevertheless, their SSC resistance reduced noticeably between 10 and 30% PPR of CO2.