Corrosion mechanism of graphitized cooling-water pipes and their protection by HVOF-sprayed WC–10Co–4Cr coatings

Cooling-water pipes in graphitization lines suffer from coupled high-temperature sulfur corrosion and erosion. This study characterizes the axial corrosion gradient of uncoated 310S pipes and evaluates HVOF-sprayed WC–10Co–4Cr coatings (100, 200, 300 μm). The uncoated pipe shows severe tip corrosion (penetration ∼316–380 μm) governed by grain boundary degradation and sulfate-induced depassivation. The 200 μm coating exhibits the best mechanical integrity (bond strength 82.0 ± 3.4 MPa, hardness 1295 HV0.1), high-temperature wear resistance (8.8-fold lower wear volume), and corrosion resistance, with continuous coverage confirmed by post-service inspection.