A study on the evaluation of creep degradation of high temperature pipeline steel by non-destructive test

In this paper, artificial creep degradation test and ultrasonic measurement for their creep degraded specimens (Cr-Mo alloy steel) were carried out for the purpose of evaluation for creep damage. Absolute measuring method of quantitative ultrasonic measurement for material degradation was established, and long-term creep degradation tests using creep life prediction formula were carried out. As a result of ultrasonic tests for crept specimens, we conformed that both the sound velocity decreased and attenuation coefficient linearly increased in proportion to the increase of creep life fraction (phi(c)). In frequency and noise analysis, it was conformed that the high frequency side spectra and central frequency components shift to low frequency band, and bandwidths decrease as increasing creep damage in backwall echo. And also, the ultrasonic noise linearly increased in proportion to the increase of creep degradation.