Experimental Study on Multi-Stress Field Accelerated Corrosion of Steel in Dry Coal Shed Industrial Environment

Steel structures in dry coal sheds serve under high temperature, high humidity and sulfur-bearing media. To reveal how typical stress fields affect the corrosion behavior and post-corrosion mechanical properties of steel, an acid-fog–stress-coupled accelerated corrosion apparatus was developed. A 0.01 mol/L NaHSO3 + 0.001 mol/L NaCl solution was sprayed onto Q355B coupons at 40 °C and RH > 95% under alternating spray-drying cycles. Six tensile-loading conditions were examined: laser-cutting residual stress (0.47 fy), wire electrical discharge machining (WEDM), welding residual stress, constant stresses of 0.40 fy and 0.56 fy, and alternating stress between them. Corrosion morphology evolved from uniform thin rust to pitting, pit interconnection and large-scale spalling, with maximum pit depth increasing from 33 μm to 392 μm in 70 days. Residual-stress specimens corroded faster than service stress specimens, and welded specimens were the most severely corroded (1.21–1.43 times the WEDM value). Strength ratios remained within 0.96–1.05, whereas the yield plateau elongation fell to 0.032% at 70 days. Pit-induced non-synchronous yielding, verified numerically, explains the loss of the yield plateau. An empirical accelerated-to-natural conversion for C4 exposure is given.