SIMULATION OF DEGRADED REPAIR WELD AND SERVICEABILITY ASSESSMENT OF PETROLEUM PRESSURE VESSEL-asme/terms-of-use

ABSTRACT In order to simulate temper and hydrogen embrittlement in 2.25Cr-iMo pressure vessel steel in the laboratory, test specimen exceeding 100 m m (4 in.) in thickness containing repair welds made with the shielded metal arc welding (SMAW) process were exposed to hydrogen environment in an autoclave. By investigating the dilution, hardness and microstructure characteristics of the specimen repair welds, it was possible to determine a standard repair technique including m i n i m u m stainless steel overlay thickness. From the test results, it was concluded that a m i n i m u m of 3.0 mm (1/8 in.) residual overlay thickness was recommended as part of the repair technique by SMAW. In addition, tensile tests of the hydrogen exposed specimens confirmed the serviceability of recent and old generation 2.25Cr-1Mo pressure vessel steel repair welds. In particular, the effect of temper and hydrogen embrittlement on serviceability was examined by detailed observation of microstructure and fracture surface of the tensile specimens. 1,INTRODUCTION In a J a p a n e s e petroleum refinery, there are significant n u m b e r of pressure vessels, heat exchangers, and piping, which has been in service for over 40 years. Recent trends of long-term continuous operation and extension of inspection intervals has made it necessary to re-examine various material properties and serviceability evaluations after repair welding and subsequent return to service of aging degraded material. Typical in-service degradation mechanisms of pressure vessels in petroleum refineries are shown in The purpose of this study to simulate temper and hydrogen embrittlement that occurs in service to pressure vessel in petroleum refineries to assess the serviceability of weld repairs to damaged steels in the laboratory, and to propose appropriate repair guidelines. This study is particularly intended to address petroleum refinery pressure vessels such as hydrocracking and hydrodesulfurization reactors, which operated in a high temperature, high pressure hydrogen environment. By the results of these experiments, it is possible to conduct serviceability assessments simulating actual operating conditions. In this study, large autoclave test equipment was utilized to contain test specimens exceeding 100 mm (4 in.) in thickness, and expose the specimen in a high temperature, high pressure hydrogen environment in order to reduce the