Abstract
Copper heat exchanger tubes in water heater have been similarly suffering from type I' pitting corrosion, which have been experienced in the pass-through soft copper plumbing tubes, under well water. Through the case examination, the result showed that type I' pitting corrosion only appears on water inlet pipes and coiled pipes under conditions of maintained cold water as well as residual carbon over 5mg/m2.
To solve this problem, the performance of 3 type heat exchangers was investigated by field test under well water. The heat exchanger with copper tubes treated by tin coating after manufacturing showed the most excellent resistance against pitting corrosion due to the stable tin oxide formation on the tin coating surface, followed by the heat exchanger made of copper tube with residual free carbon below 4mg/m2 which also showed excellent pitting corrosion resistance. However the heat exchanger with manufactured Cu-0.24 mass%Sn alloy tube corroded in either case: with or without carbon film. Consequently, it can be stated that residual free carbon has certain relevance to copper, as so for Sn concentration to Cu-Sn alloy concerning the occurrence of pitting corrosion.
