Power Generation, ESB, Head Office, Lower Fitzwillian Street, Dublin 2, Ireland
Abstract:
The present paper attempts to describe a series of detailed remaining life assessments of a cracked reducer weld location in a attemperator steam line in a 120 MW fossil-fired unit. Crack growth occurred by either pure fatigue or by creep-fatigue depending upon the combinations of stress and crack depth, i.e. maximum stress intensity level, KMAX. From consideration of certain fatigue and creep threshold details and measured fatigue striation spacings on the failure surface a stress of 80 MPa was estimated to be driving the cracking process. Also high temperature fatigue crack growth data was treated in terms of a series of constant probability crack growth curves which allowed real probability values to be assigned to any particular remaining life assessment. It was shown that for probability levels of 10?4 and an estimated active stress of around 80 MPa the remaining life of initial 4 mm and 7 mm deep cracks was 231 and 87 starts respectively.