Embrittlement evaluation and lifetime assessment of hydrocracking pressure vessel made of 3Cr–1Mo low-alloy steel

The Cr–Mo steels which are widely used for pressure vessels in refineries and petrochemical plants, have a potential for hydrogen and temper embrittlement. During long-time service the embrittlement leads to decrease of the critical flaw size of brittle fracture and/or to the reduction of the remaining life of a pressure vessel. In this investigation the effect of high temperature and high pressure hydrogen on a vessel, made of 3Cr–1Mo low-alloy steel is studied. Inspections show that the only detected crack in the base metal is originally formed by welding defects and calculations show that it will not grow up. Therefore, it is predicted that the operation of the pressure vessel in normal condition and under regular supervision can be continued.