Abstract: Current DL/T 5054 and GB 50764 cover only design-stage compliance, while defect-bearing thresholds for operating waste-to-energy (WtE) plant steam-water piping supports remain blank. Based on census data of 444 hanger points from 12 operational WtE plants in the Yangtze River Delta, a "CAESAR II global load extraction → ANSYS local refined analysis" relay model is established, with parametric coupling of three defects: hanger rod deflection angle, root incomplete fusion of the lower flange, and spring pre-compression deviation. Results show that when θ=5° and a=2 mm, σmax reaches 172 MPa (1.09σ); with additional 15% spring deviation, σmax rises to 196 MPa (1.25σ), approaching yield. A three-level (green/yellow/red) threshold is proposed, and a 10 mm Q235B reinforcing plate reduces σmax to 121 MPa (0.77σ) at 0.5% of the full-replacement LCC. The threshold and workflow can be embedded into plant DCS for quantitative maintenance.