Estimation of Creep Damage for the Components of Mod. 9Cr-1Mo Steel. 3rd Report, Creep Damage Assessment for Seam Weld in Internally Pressurized Pipe.

Abstract

In order to establish the assessment method of creep damage for high temperature piping components made of modified 9Cr-1Mo steel with seam weld, subjected to internal pressure, the internal pressure creep tests and FEM stress analysis were done for cylinders with seam weld. In internal pressure creep tests, the creep rupture occurred at fine grained heat affected zone (F. G. HAZ), caused by cracking originated from the formation of voids. The correlation between void area fraction and creep damage was obtained. The morphology of voids were quite similar to that observed in welded joint specimens in uni-axial creep tests. Stress distribution of seam weld cylinder under internal pressure creep showed the higher circumferential stresses in F. G. HAZ where creep rupture occurred. The distribution of circumferential stress and creep damage calculated by using circumferential stress along specimen thickness were quite similar to that of void area fraction in internal pressure creep test. The creep damage in seam weld pipe under internal pressure creep could be estimated by the observation of void area fraction in F. G. HAZ.