TY - GEN
T1 - A STUDY OF STRESS RELAXATION CRACKING MECHANISM IN A 347H STEEL PIPE-SHOE WELDMENT AFTER FIVE-YEAR SERVICE
AU - Wang, Yiyu
AU - Yang, Yi
AU - Gao, Yanfei
AU - Penso, Jorge
AU - Feng, Zhili
N1 - Publisher Copyright:
Copyright © 2023 by The United States Government.
PY - 2023
Y1 - 2023
N2 - 347H stainless steel has been widely used for piping, furnace tubes, pressure vessels and other pressure boundary components in oil refining plants because of its excellent high-temperature strength and high oxidation and sulfidation resistance. However, cracking failures in 347H steel weldments could occasionally occur and significantly shorten lifetimes of those welded heater components. In this work, a comprehensive metallurgical analysis was conducted on a cracked 347H steel pipe-shoe weldment after only about 5-year service at a petroleum refinery. Premature cracking mechanisms of this pipe-shoe weld were studied in detail by correlating multiple factors, including service conditions, weld configuration, chemical compositions, and microstructure degradations. Microstructural characteristics of different regions in the weld, including fusion zone, heat affected zone, and base metal, were examined using multi-scale microscopic techniques. The results show the cracks initiated at the fusion boundary in the weld toe and propagated towards the heat affected zone and base metal in an intergranular manner. The cracks grew via connecting grain boundary cavities formed during service. Insufficient precipitation strengthening from M23C6, and MX assisted nucleation and growth of cavities along grain boundaries was observed. Ferrite formation along grain boundary induced a high localized strain along grain boundaries, which also favored crack propagation. Due the thermal gradient during service, the microstructure degradation (cavities) along the pipe wall thickness direction was not uniform, the region near the outer diameter has more cavities than that of the inner diameter wall. It is suspected that the high stresses in the weld toe region caused by the deviation from component’s original design and rotational forces on the weld resulting from the weld configuration, were the main external driving force responsible for this observed early failure. A combination of stress relaxation cracking, thermal stresses, and microstructure degradation was likely the main culprit for this premature cracking issue.
AB - 347H stainless steel has been widely used for piping, furnace tubes, pressure vessels and other pressure boundary components in oil refining plants because of its excellent high-temperature strength and high oxidation and sulfidation resistance. However, cracking failures in 347H steel weldments could occasionally occur and significantly shorten lifetimes of those welded heater components. In this work, a comprehensive metallurgical analysis was conducted on a cracked 347H steel pipe-shoe weldment after only about 5-year service at a petroleum refinery. Premature cracking mechanisms of this pipe-shoe weld were studied in detail by correlating multiple factors, including service conditions, weld configuration, chemical compositions, and microstructure degradations. Microstructural characteristics of different regions in the weld, including fusion zone, heat affected zone, and base metal, were examined using multi-scale microscopic techniques. The results show the cracks initiated at the fusion boundary in the weld toe and propagated towards the heat affected zone and base metal in an intergranular manner. The cracks grew via connecting grain boundary cavities formed during service. Insufficient precipitation strengthening from M23C6, and MX assisted nucleation and growth of cavities along grain boundaries was observed. Ferrite formation along grain boundary induced a high localized strain along grain boundaries, which also favored crack propagation. Due the thermal gradient during service, the microstructure degradation (cavities) along the pipe wall thickness direction was not uniform, the region near the outer diameter has more cavities than that of the inner diameter wall. It is suspected that the high stresses in the weld toe region caused by the deviation from component’s original design and rotational forces on the weld resulting from the weld configuration, were the main external driving force responsible for this observed early failure. A combination of stress relaxation cracking, thermal stresses, and microstructure degradation was likely the main culprit for this premature cracking issue.
KW - 347H Steel
KW - Characterization
KW - Oil Refining
KW - Pipe Shoe Weldment
KW - Premature Failure
KW - Stress Relaxation Cracking
UR - http://www.scopus.com/inward/record.url?scp=85179894561&partnerID=8YFLogxK
U2 - 10.1115/PVP2023-105755
DO - 10.1115/PVP2023-105755
M3 - Conference contribution
AN - SCOPUS:85179894561
T3 - American Society of Mechanical Engineers, Pressure Vessels and Piping Division (Publication) PVP
BT - Operations, Applications and Components
PB - American Society of Mechanical Engineers (ASME)
T2 - ASME 2023 Pressure Vessels and Piping Conference, PVP 2023
Y2 - 16 July 2023 through 21 July 2023
ER -