Stress Corrosion Cracking Evolution of Low Alloy Downhole Tubular Steel in CO2 Containing Environment at 175 °C

Abstract Slow strain rate tests were performed to study the stress corrosion cracking evolution of a low alloy tempered martensite downhole tubular steel at 350 °F (175 °C) in CO2 saturated environment. Experiments were carried out in a high pressure high temperature nickel base super alloy autoclave which was connected to a constant extension rate machine. Slow strain rate tests were interrupted at specific strain values to examine the specimens and study crack initiation and growth. It was found that up to a certain strain value cracks didn’t form, but after that, formation of cracks on the gauge length of the tensile specimens was observed and increasing the strain value cracks grew both in length and width. Crack growth velocity estimated from the length of the largest (deepest) crack and the experiment time period after initiation. Corrosion products were studied and identified using scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction, and after cleaning the corrosion products cracking behavior and cracks’ evolution was studied using scanning electron microscopy. It was proposed that the formation of protective corrosion products on the steel surface and local break down of the scale lead to localized anodic dissolution and crack propagation.