Abstract
This work was undertaken as part of a contract from the Department of the Environment to investigate the potential of materials used in plumbing systems to contaminate the supply. Particular attention was paid to soldered joints as these will constitute the major source of lead contamination in the future. This report describes a galvanic corrosion cell for measuring corrosion rates of solder in potable waters and the work to establish that its corrosion behaviour reflected that of an authentic soldered joint. The work has established that more than a quantitative difference exists between the galvanically mediated corrosion of lead and that of the freely corroding metal. Qualitative differences also occur that are of significance to the Water Industry's treatment approach to reduce lead contamination problems. The test cell was used to investigate the effect of various water quality parameters on corrosion rates. The parameters found to stimulate corrosion were low pH and high chloride and nitrate concentrations. Sulphate, silicate and zinc were all found to reduce corrosion. Zinc was discovered to be an inhibitor from an investigation into the effect of flux residues. The material used contained zinc chloride as the active ingredient. Carbonate hardness and orthophosphate were both found to be without effect on corrosion rates. This was surprising, especially as the latter is successfully used to overcome contamination problems from lead pipe. Using the corrosion rates measured in this work, attempts were made to quantify the contamination risk from soldered joints. The general conclusion was that only by limiting the area of solder exposed in the bore of the tube could a significant long term problem be avoided. As this depends upon the individual skill of the person making the joint, the only sure way of avoiding contamination is to specify lead free solders.