Study on Mechanical Strength of Welded Joint of High Temperature and High Pressure Pipe in Ultra-supercritical Secondary Reheating Unit

Ultra-supercritical two-stage reheat power generation units operate under extreme conditions with 630 ℃/30 MPa parameters. The mechanical strength of high-temperature/high-pressure pipe welding joints critically impacts operational safety. Through optimized welding processes, P92 steel and Super304H stainless steel pipe joint specimens were fabricated and subjected to systematic mechanical property evaluations. High-temperature tensile tests revealed that P92 steel joints achieved a tensile strength of 485 MPa at 630 ℃, equivalent to 87.3% of the base material′s strength, while Super304H joints demonstrated 520 MPa tensile strength. Impact toughness tests identified the P92 side heat-affected zone as the weakest link, with an impact energy of merely 42 J. Long-term creep testing confirmed a creep fracture strength of 135 MPa after 200000 hours, achieving a safety factor of 2.2 times and meeting the long-term operational safety requirements for ultra-supercritical units.