Abstract
In this work, multi-scale metallurgical characterizations with advanced microscopy techniques were conducted on an ex-service girth weld between a SA-182 forge 91 (F91) steel reducer to a SA335 pipe 91 (P91) steel header after 141,000 hours (16 years) service at a coal-red power plant between 1991 and 2015. Multiple metallurgical factors, including compositions, inclusions, precipitates, and hardness, were analyzed in comparison for the F91 and P91 steels. The results not only gain an in-depth understanding of creep deformation mechanisms in 9Cr steel welds, but also provide baseline information for remaining lifetime assessments of those service-aged steam components. The results show highly nonuniform creep degradation and damages were observed on the F91 and P91 sides. Base metal and heat affected zone (HAZ) on the F91 steel side experienced a higher degree of microstructure degradation with lower hardness and a higher fraction of creep cavities. Softened zones with lower hardness values were identified in both HAZs of F91 side and P91 side. However, the most creep damaged zones (CDZ) with the highest number density of cavities are not the identified softened zones. In the CDZ, creep cavities are always associated with coarse precipitates (Laves phase, Z phase) and large inclusions (Al oxides, AlN, MnS). A higher fraction of inclusions, coarser precipitates, and larger grain size in F91 steel put itself and its HAZ more vulnerable to creep damages, especially the infamous Type IV cracking.
| Original language | English |
|---|---|
| Title of host publication | Materials and Fabrication |
| Publisher | American Society of Mechanical Engineers (ASME) |
| ISBN (Electronic) | 9780791886182 |
| DOIs | |
| State | Published - 2022 |
| Event | ASME 2022 Pressure Vessels and Piping Conference, PVP 2022 - Las Vegas, United States Duration: Jul 17 2022 → Jul 22 2022 |
Publication series
| Name | American Society of Mechanical Engineers, Pressure Vessels and Piping Division (Publication) PVP |
|---|---|
| Volume | 4-B |
| ISSN (Print) | 0277-027X |
Conference
| Conference | ASME 2022 Pressure Vessels and Piping Conference, PVP 2022 |
|---|---|
| Country/Territory | United States |
| City | Las Vegas |
| Period | 07/17/22 → 07/22/22 |
Funding
This work is funded by the Department of Energy Office of Fossil Energy’s Crosscutting Research Program (FWP-FEAA118) and the Strategic Partnership Project (NFE-20-08195) with Electric Power Research Institute. DOE program manager was Dr. Vito Cetro. 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. Corresponding author: [email protected]. 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).