Effect of service exposure on the mechanical properties of 2.25Cr–1Mo pressure vessel steel in a hot-wall hydrofining reactor

Life assessment for hydrocarbon processing plant components is important for both service life extension and also to minimize the potential for premature catastrophic failure. In this paper, the degradation of 2.25Cr–1Mo pressure vessel steel in a hot-wall hydrofining reactor is investigated. A test block containing a weld is exposed to the chemical service environment present within a reactor. After removal from the reactor, chemical composition, tensile behavior, impact performance are quantified and the microstructure characterized using scanning electron microscopy (SEM). Results from the tensile tests indicate that the irradiated weld and base material had similar stress–strain response. Results from the Charpy V-Notch (CVN) impact tests demonstrated that the toughness of both the base material and weld were degraded with the degradation and embrittlement of the weld zone being significantly higher than the base material. Through careful processing of additional samples extracted from the test block, using (a) de-hydrogen treatment to remove the hydrogen, (b) hydrogen charging to enrich the hydrogen content to saturated condition and (c) de-brittleness treatment, additional fracture experiments confirmed that the toughness degradation was mainly caused by high temperature tempering and not by the effects of hydrogen embrittlement due to long-term exposure.