Experimental observation of creep damage evolution in seam-welded elbows of mod. 9Cr-1Mo steel

Seam-welded elbows and straight pipe of the same size as actual high temperature reheat piping for boiler applications were manufactured, and internal pressure creep testing was conducted. Uniaxial creep testing was also performed in order to compare creep damage behaviours. Comparing the observed creep damage evolution and stress analysis results, a creep damage estimation method was discussed. Creep damage distribution varied depending on ovality in the cross sections of the seam-welded elbows. It is important that FEM models for creep analysis incorporate measurement results for the cross-sectional shape of seam-welded elbows. Using the nominal stress of the specimens and the average creep rupture data from small size uniaxial welded joint tests, a simplified prediction method was discussed, which is applicable to creep rupture time prediction for both large creep specimens and seam-welded elbows.