In order to simulate temper and hydrogen embrittlement in 2.25Cr-1Mo pressure vessel steel in the laboratory, test specimen exceeding 100 mm (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 minimum stainless steel overlay thickness. From the test results, it was concluded that a minimum 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.

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