Proposal of Creep Damage Evaluation Procedures for Power Boiler Mod.9Cr-1Mo Weldments (First Report: Uniaxial Loading)

摘要

In order to develop the evaluation procedures of creep damage for Mod.9Cr-1Mo weldments in power boiler steam piping and header, a series of uniaxial creep tests with transverse welded joint specimens were performed at 650°C under 58.8MPa. Creep voids were observed through the thickness of specimens when tests were interrupted at the stage of 15%, 29%, 43%, 53%, 88% and 100% of rupture time. Ultrasonic noise method was applied to the measurement of creep damage. Specimen was fractured at type Ⅳ region and creep voids were found at the softening regions of HAZ in all interrupted specimens. When creep void area ratios were calculated for the interrupted specimens, creep void area ratio was proved to increase as the creep life ratio increased. It seems that creep damage can be evaluated from the correlation curve between the creep void area ratio and creep life ratio. Ultrasonic noise method is based on the back scattering from creep void. Ultrasonic noise ratios, which are defined compared with undamaged material, had good correlation with the creep life ratios. Ultrasonic noise method seems to be effective for the evaluation of creep damage under surface.