長期間高温高圧水素環境下で使用された 0.5Mo 鋼装置における粒界割れ

概要

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Remarkable intergranular cracks and local bubble cavities along grain boundaries were detected in a 0.5 Mo steel channel head of a heat exchanger which had been operated in a hydrodesulfurization unit for nine years under a condition well below the operating limit of NELSON chart. The same kind of intergranular cracks in a 0.5 Mo steel feed line pipe were found at welded areas in a periodical inspection during the shut down maintenance period after operation for fifteen years in a catalytic reforming unit. Metallurgical investigation and hydrogen exposure tests at 320 and 400℃ under 9.81 MPa (100 kgf/cm^2) were performed to manifest the cause of damage occurred in the materials. The as-received channel head steel whose microstructure composed of untempered ferrite and pearlite exhibited high susceptibility to intergranular cracking due to hydrogen attack in such case that only M_3C carbide precipitated. Heat treatment at 650 to 700℃ for stress relief was found to be most desirable for securing resistance to hydrogen attack in such hot-formed 0.5 Mo steels as vessel heads, pipes and its fittings to be used in hydrogen environment at elevated temperatures and pressures.
社団法人日本鉄鋼協会の論文
1985-09-01