Influence of heat treatments on the susceptibility of 9%Ni low carbon steel to sulfide stress corrosion cracking

Abstract

Low carbon steels with Ni addition are selected to low temperature and cryogenic services. Recently, 9%Ni low carbon steel has been selected to cryogenic pipes and vessels in the oil and gas off-shore platforms where traces of H2S may be present in the fluid process. In this work, specimens from a 9%Ni low carbon steel were submitted to four different heat treatments: quenching (Q), quenching and tempering at 400 °C (QT400), quenching and tempering at 600 °C (QT600), and quenching, lamellarizing and tempering (QLT). The susceptibility to sulfide stress corrosion cracking (SSCC) was evaluated by slow strain rate tensile tests (SSRT) in aqueous solution with pH 2.7–3.0 and H2S partial pressure of 20 mbar. Condition QT600 was the less susceptible to SSCC. The results were discussed taking into account the microstructural analysis performed by scanning electron microscopy and magnetic measurement of austenite.