STRESS RELAXATION CRACKING OF WELDED JOINTS IN THICK SECTIONS OF A TP347 STABILIZED GRADE OF STAINLESS STEEL

摘要

This paper discusses reactors that experienced numerous cracking problems, over a 8-year period, where cracks are confined to the welded zones. The reactors were in hydrocarbon service. The material of construction is solid TP347 stainless steel and the original construction welds as well as initial repair welds were done with E347-16 consumables. Other factors playing a role are: more than 60 transients resulting in creep-fatigue as well as the poor creep-rupture ductility of welds. Inner surfaces are subject to coke formation and a small degree of low temperature carburization and sulfidation at temperatures in the region of 560°C. Welded joints that have cracked are where the parent material is above 12mm in thickness and where grain sizes are coarser than ASTM no 3.5. Concerns of weld quality, triaxial stress raisers, heat treatment practices, melt practices and sigma phase formation is included. During shut-down conditions some polythionic acid stress corrosion cracking had also been identified. This paper discusses and reveals examples of stress relaxation cracking as well as classical examples of white-phase-fractures. Corrective recommendations, using leaner E16.8.2-15 consumables for repair welding are also covered.