Inner Pressure/Bending Creep Test on Circumferentially Welded Large Diameter Pipe of Grade 91 Steel: Creep Damage Mechanism and Applicability of NDE

In this study, an inner pressure/bending creep test on a circumferentially welded large diameter 9Cr steel pipe was conducted at a temperature of 650°C to investigate the creep damage mechanism and applicability of nondestructive evaluation techniques to the detection of creep damage. The test was interrupted before steam leakage based on a change in axial strain at the surface of the welded joint. Surface cracks were observed at the lower part of the specimen along the circumferentially welded joint where axial tensile stress was applied. As a result of phased array ultrasonic inspection, indications of internal defects were first detected along welded joints where the failure life ratio was 54% with the range of indication increasing with test time. The indications of internal defects were in good agreement with observations of sectional views in welded joints.