Reasons for Corrosion Failure of Sewage Pipe Section in Hydroprocessing Unit

Corrosion cracking occurred in a sewage pipe section of a raw material transport pipeline of a hydrogenation unit. The reasons of corrosion failure of the pipe section were analyzed by means of macro and micro morphology observation, chemical composition analysis, corrosion product composition analysis and metallographic examination, and the corresponding improvement measures were put forward. The results show that the chemical composition and microstructure of the pipe section were normal, and the material of the pipe section was not sensitized. The cracks extended from the inner wall to the outer wall of the pipe section, showing the obvious feature of bifurcation, and were transgranular cracks. Chlorine element remained in the corrosion products on the fracture surface. Stress corrosion cracking caused by chloride ion could be inferred from the crack characteristics and the composition of corrosion products. There was a large temperature difference at both ends of the pipe section, resulting in water phase precipitation in partial zone. And corrosive chlorine in the medium accumulated in the water phase, forming a stress corrosion cracking environment.