Abstract: Aiming at the leakage case of the tube joint of high-pressure air cooler in a diesel hydrogenation unit during prevulcanization, this paper conducts macroscopic inspection, chemical composition analysis, metallographic structure analysis, fracture analysis and hardness test on the failure sample combining with two working conditions of production operation and presulfurization. It is confirmed that excessive hardness of the weld and heat-affected zone of the tube plate side of the air cooler is the main reason for the wet hydrogen sulfide stress corrosion cracking. And it is concluded that the wet hydrogen sulfide stress corrosion cracking is more likely to occur under presulfurization condition. Meanwhile, the paper also analyzes the welding process of the pipe joint of high-pressure air cooler and puts forward the improvement measures.

Key words: diesel hydrogenation, high-pressure air cooler, prevulcanization, wet H₂S, sulfide stress corrosion cracking/SSC