In this study, an inner pressure/bending creep test on a circumferentially welded, large diameter pipe of grade 122 steel was carried out under conditions where the test temperature was 923 K and the expected rupture time was 8,700 h to investigate creep damage mechanisms and the applicability of nondestructive evaluation techniques for the detection of creep damage. Deformation of the specimen rapidly increased at 7,894 h, and the creep test was interrupted. Surface cracks were observed on the lower part of the specimen along the circumferentially welded line where axial tensile stress was applied. As a result of phased array ultrasonic inspection, indications of internal defects were detected along welded lines where no indication was detected in previous inspection at 6,520 h, and it was predicted that cracks propagated along the fine-grained heat-affected zone (HAZ) from within the specimen to near the inner and outer surfaces. The indications of internal defects were in good agreement with observations from sectional views of the welded joints.

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