Crack Analysis and Weldability Restoration of 800H Alloy High-Temperature Steam Pipelines

The 800 alloy is extensively utilized in high-temperature equipment owing to its exceptional high-temperature strength and resistance to oxidation and corrosion. However, during prolonged service, the alloy undergoes microstructural changes, such as carbide precipitation, which weaken its integrity. Under the influence of operational stress, cracks may develop, ultimately leading to component failure. This study focuses on the failure analysis of cracks that formed after prolonged operation in an 800H alloy high-temperature steam pipeline, specifically in areas near the valve and weld joint. Detailed examinations of crack morphology and oxidation products revealed that the primary failure mechanism was stress relaxation cracking. To restore the pipeline’s functionality and extend its operational lifespan, a thermal performance restoration approach was applied. Samples from the 800H alloy were subjected to solution annealing—a heat treatment process designed to enhance its weldability. Post-treatment welding trials demonstrated a notable improvement in the alloy’s welding performance. Non-destructive testing confirmed the absence of cracks, while microstructural analysis verified that the heat treatment effectively eliminated microcracks in the weld joints.