Pitting Corrosion in Copper Tubes in Cold Water Service

Abstract

The occurrence of pitting corrosion in copper tubes carrying cold supply waters has been investigated in relation to (a) carbon residues in the bore of the tube from the bright annealing operation, (b) the hardness and composition of the metal, and (c) water composition. The electrode potential of tubes in several supply waters has been used to assess their susceptibility to pitting corrosion. It is concluded that pitting occurs only in certain types of water with a low level of organic matter in tubes containing more than a critical amount of carbon residue in the bore. Hardness of the metal appears to have little effect on susceptibility to pitting corrosion, but the addition of about 1 percent tin to the copper substantially reduces the rate of pitting for a given level of carbon contamination in the bore. The significance of these findings is reviewed in the light of service experience with copper water tubes in the United Kingdom.