Effect of Acid Pickling and Passivation Treatment on Circumferential Weld Corrosion Resistance of 316L/L415 Mechanically Bimetallic Composite Pipe

Aiming at the problem of corrosion and leakage in the circumferential weld of 316L/L415 bimetal mechanical composite pipe, a pickling passivation solution (25% HNO₃+5% HF+70% H₂O) was prepared for pickling passivation (PP) treatment. Corrosion resistance of the welded samples before and after pickling passivation was compared using morphology observation, electrochemical test, and pitting corrosion test. The results showed that the surface of the sample after PP teratment became smooth, bright and clean. After PP teratment, the content of corrosion resistance elements Cr and Ni on the surface of the weld and heat-affected zone specimens increased significantly, but the content of Cr and Ni of the base metal changed little, the self-corrosion potential of base metal, weld and heat-affected zone samples all shifted positively, and the corrosion rate lowered. PP treatment could generate a new and denser passivation film on the surface of the girth weld, which significantly improved the corrosion resistance of the girth weld of the 316L/L415 composite pipe.