Investigation of Hydrogen Embrittlement of High Strength Pipeline Steels under Cathodic Protection

Abstract With the wider application of pipeline steels higher than API X80 grade, the hydrogen embrittlement risk induced by the hydrogen evolution effect under cathodic protection has been recognized. Since the increased strengthening of pipeline steel might significantly increase the hydrogen cracking sensitivity, a greater understanding on the different criteria of cathodic protection potential or current density compared with those of traditional pipeline steels are required. This paper focuses on the hydrogen embrittlement behaviors of API X70, X80 and X90 high strength pipeline steel under cathodic protection in soil simulation conditions. The uptake and diffusion of hydrogen in the steels under different cathodic protection levels were analyzed by hydrogen permeation test and hydrogen content measurement. Slow strain rate testing (SSRT) under cathodic conditions as well as mechanical performance degradation testing after long term immersion were used to determine the hydrogen embrittlement (HE) susceptibilities of the three kinds of steel. The results showed the changes of hydrogen diffusion rate, hydrogen accumulation limit and hydrogen embrittlement with the increased steel strength under different soil and cathodic protection conditions.