Multi-mechanism synergistic failure analysis and quantitative characterisation of S30408 heat exchange tubes in an economiser of an oil residue hydrogen production unit

After one year of operation, S30408 heat exchange tubes in an economiser of an oil residue hydrogenation unit leaked. Examinations included macroscopy, chemical analysis, hardness testing, scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), micro-area X-ray diffraction (micro-XRD), metallography, and electron backscatter diffraction (EBSD). Severe work hardening at the elbow increased hardness from 165.3 to 332.7 HV10, raised geometrically necessary dislocation (GND) density from 0.75 × 10¹⁴ to 3.41 × 10¹⁴ m−², and reduced Σ3 twin boundaries from 42.0% to 27.1%. Corrosion products confirmed sulfuric acid dew point corrosion and upstream catalyst residue synergy. A quantitative environment–material–stress model yielded ηenv = 2.15, ηmaterial = 2.65, and φ = 0.37; ηenv × ηmaterial = 5.70 quantifies the combined acceleration by V/Mo residues and cold-worked microstructure. The measured average corrosion rate was 0.200 mm/a. The model predicted a failure time of 1.07 years, matching the actual service life. Sulfide stress corrosion cracking (SSC) dominated, reducing the failure time from ∼10.0 years to ∼1.2 years. Preventive measures include selecting duplex or stabilised austenitic stainless steel, controlling cold deformation, and solution heat treatment after cold forming.