Integrity Assessment of Similar and Dissimilar Fusion Welded Joints of Cr-Mo-W Ferritic Steels under Creep Condition

Integrity of similar and dissimilar fusion welded joints of grade 22, grade 9, grade 91 and grade 92 steels under creep conditions has been assessed. Similar joint of the steels possesses lower creep rupture strength than the corresponding base steel. Premature failure of the joint occurs at outer edge of heat affected zone (HAZ), called as type IV cracking. Extent of type IV cracking depends on the steel, adopted welding technique and thickness of the joint. Ferritic/ferritic dissimilar weld joint suffers from the type III cracking in coarse grain HAZ in low-Cr steel. Creep cavitation occurs in the soft zone formed in the coarse grain HAZ of low-Cr steel due to the migration of carbon from low-Cr to high-Cr steels. Ferritic/austenitic dissimilar weld joint of the steels welded employing Inconel welding consumable exhibits extensive creep strength reduction. Failure occurs at ferritic/austenitic weld interface and is associated with nucleation of creep cavity at interface precipitate particles. Cracking behaviour of the similar and dissimilar joints of the steels and their relative severity have been assessed considering the FE analysis of stress distribution across the joints and microstructural investigation.