Abstract
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.
| Original language | English |
|---|---|
| Title of host publication | Operations, Applications and Components |
| Publisher | American Society of Mechanical Engineers (ASME) |
| ISBN (Electronic) | 9780791887493 |
| DOIs | |
| State | Published - 2023 |
| Event | ASME 2023 Pressure Vessels and Piping Conference, PVP 2023 - Atlanta, United States Duration: Jul 16 2023 → Jul 21 2023 |
Publication series
| Name | American Society of Mechanical Engineers, Pressure Vessels and Piping Division (Publication) PVP |
|---|---|
| Volume | 6 |
| ISSN (Print) | 0277-027X |
Conference
| Conference | ASME 2023 Pressure Vessels and Piping Conference, PVP 2023 |
|---|---|
| Country/Territory | United States |
| City | Atlanta |
| Period | 07/16/23 → 07/21/23 |
Funding
The research and development work was performed at the Oak Ridge National Laboratory, which is managed by UT-Battelle LLC for the US Department of Energy under contract DE-AC05-00OR22725. The authors would like to thank Mr. Alan Frederick for the metallurgical specimen preparation and Mr. Calvin Foong for shipping the samples and providing insight information needed in this work. This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doepublic-access-plan).
Keywords
- 347H Steel
- Characterization
- Oil Refining
- Pipe Shoe Weldment
- Premature Failure
- Stress Relaxation Cracking