Enhancing stress corrosion resistance of gas cylinders through Ni-electroplating

• Ni-coating protects 34CrMo4 steel against sulfide stress corrosion cracking. • Stress-induced periodic crack rings were observed in the Ni-coatings on the steel substrate. • The widths of the periodic rings and associated cracks increase with the Ni coating thickness. • The failure mechanisms and damage characteristics of the Ni plating under stress were analyzed. • The application of a Ni-coating decreases the surface roughness of 34CrMo4 steel. The protective effect of electroplated nickel on the resistance of 34CrMo4 steel to sulfide stress corrosion cracking (SSC) and hydrogen-induced cracking (HIC) was investigated. Nickel electroplating significantly reduced the surface roughness and improved the SSC/HIC resistance of the steel. Under applied stress, periodic crack rings (200–400 μm wide) formed in the Ni coating due to steel elongation and the mismatch in stress–strain behavior between the coating and substrate. These cracks, with inter-ring widths of 30–90 μm, served as pathways for H 2 S ingress. An increase in plating thickness resulted in wider fracture rings and inter-ring cracks, attributed to the thickness-dependent mechanical behavior of the Ni coating. Notably, no hydrogen-induced cracking was observed in Ni-plated specimens under zero stress, indicating that applied stress is the dominant factor in failure of the protective layer. These findings highlight the dual role of Ni electroplating: improving surface finish and enhancing resistance to H 2 S-induced degradation. This study provides insights into optimizing Ni plating parameters to improve the performance and durability of 34CrMo4 steel components in H 2 S service environments.