技術論文高温高圧水素に対する圧力容器の供用適性評価技術長割れ（Hydrogen Environment Assisted Cracking : HEAC）を評価した最近の研究事例を紹介する。さらに、その研究で得られた水素環境助長割れの進展速度、破壊靭性を実機リアクターの溶接継手へ適用し、亀裂進展評価したケーススタディについて述べる。 The code and standard for construction of pressure vessels such as ASME BPVC Section VIII, Division 2 generally do not permit any crack-like flaws to exist in welded joint in the design and fabrication stages, however, the Fitness-For-Service （FFS） code such as API579-1/ASME FFS-1 provides the procedure for evaluating acceptable crack size during service by fracture mechanics and stress analysis （e.g. welding residual stress）. Furthermore, by evaluating the critical crack size through crack growth analysis applying the in-service environment-induced crack growth rate and fracture toughness to the crack-like flaws detected by shutdown inspection （SDI）, even in pressure vessels where they have been observed to grow during service, continuous operation is accepted until one of them is reached to the critical crack size （remaining life period）, note, however that the crack growth analysis does not guarantee the critical crack size and/or the remaining life period, based on the premise that the repair weld including removal of crack-like flaws and/or the replacement will be performed as soon as possible, even within the remaining life period. Therefore, as the use of various plant equipment become longer, FFS assessment, which technically and quantitatively evaluates the life cycle of pressure equipment, will play one of the most important role in future plant operations. It has been about 25 years since petroleum refining reactors used in hydrocracking and hydrodesulfurization process have been made of 2.25Cr-1Mo-V steel. The reactor is designed to be operated continuously for decades, and has been constructed to be highly reliable, including the welded joints, to withstand high-temperature, high-pressure hydrogen service, but as life cycle management such as assessments of minimum pressurized temperature （MPT） and remaining life is required for efficient plant operation, material properties to predict aging deterioration are becoming necessary. This paper introduces the recent research examples in which hydrogen environment assisted cracking （HEAC） initiation was reproduced in the welded joint simulating a heavy wall F22V reactor based on the results of Finite Element Method （FEM） simulating temperature, stress and diffusive hydrogen distributions that occur in the reactor wall during operating cycle. In addition, the case study is presented in which the critical crack size each for hydrogen-pressurization at R.T. and remaining life was evaluated through crack growth analysis applying the crack growth rate and fracture toughness derived by HEAC initiation obtained in the above research to the welded joint of reactor under consideration.（18）Synopsis
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