Leakage Failure Reason of B30 Alloy for Heat Transfer Pipe

The heat transfer tube of an auxiliary condenser for a marine vessel was a B30 copper-nickel alloy tube, and corrosion and leakage occurred after 20 days of service. The causes of perforation and leakage of the copper-nickel alloy pipe were analyzed by means of macro inspection, microstructure analysis, chemical composition analysis, and TEM grain boundary analysis. The results showed that the inner wall of the copper-nickel alloy pipe contained carbon and oxygen attachments, which reduced the compactness and integrity of the passivation film and formed pitting on the inner wall. The alloy matrix at the pitting was de-nickeled in weak alkaline seawater, and the intrusion of Cl^- caused the metal matrix and the passivation film to form galvanic corrosion, which eventually led to the perforation and leakage of the copper-nickel alloy pipe.