ASSESSMENT OF CREEP CRACK GROWTH RATES FOR GRADE 91 WELD JOINT AT 550 degrees C

This study presents assessment of creep crack growth rates (CCGRs) for the base metal (BM), weld metal (WM), and heat affected zone (HAZ) of Gr. 91 weld joint, which was prepared by a shield metal arc weld (SMAW) method. A series of tensile, creep, creep crack growth (CCG) tests were performed for the BM, WM, and HAZ at the identical temperature of 550 degrees C. The CCGR laws for the BM, WM and HAZ were constructed and compared in terms of a C*- fracture parameter. In addition, the CCGR law tested for BM was compared to that of RCC-MRx code. For a given value of C*, the WM and HAZ were almost similar in the CCGR, but they were significantly faster than the BM. This reason was closely attributed to the higher creep rate in the WM and HAZ than the BM. Currently elevated temperature design (ETD) code in French, RCC-MRx was found to be non-conservative in the CCGR when compared with the present investigation.