Failure analysis of heat affected zone in welding of 90/10 copper-nickel ring

The corrosion failure of 90/10 copper-nickel ring in a ship’s pipeline was investigated using metallographic observation,electron probe and electrochemical tests. The results showed that there was a large difference in the composition of the weld and the heat affected zone,which results in a large difference in electrode potential. Under the action of seawater,the galvanic corrosion occurred in the adjacent zones of the heat affected zone and the weld,and the heat affected zone with low electrode potential was eroded and thinned. The grains in the heat affected zone were recrystallized due to the welding heat cycle,and the grain grown significantly. The grain boundary of the coarse-grained microstructure becomes the preferential channel of corrosion,which results in the shedding of the entire grain and accelerates the corrosion process.There was typical intergranular corrosion morphology in the heat affected zone. Therefore,the failure of 90/100 copper-nickel ring results from a combination of intergranular corrosion and galvanic corrosion.