Failure of a Seamless 2-1/4Cr – 1Mo Hot-Reheat Pipe Bend: Metallurgical Considerations

Following the unexpected failure of a seamless hot-reheat pipe bend at Belledune Unit #2, New Brunswick, Canada, after 113,230 hot operating hours, an extensive metallurgical investigation was performed by RPC to assess the metallurgical condition of the bend, to identify the reasons for the premature failure and to evaluate the condition of the remaining pipe bends at the station. The metallurgical investigation included both on-site metallographic replication and examination of the bend material, as well as grain growth trials and mechanical tests, including short-term tensile, creep rupture and Charpy impact tests. The pipe bend was of P22 type steel of the correct composition but was extremely coarse grained. This extreme grain size resulted in low creep rupture ductility and promoted notch brittleness of the bend material in creep.