AWS WHC-5.05:2015

Lead and Zinc
Scope : Lead (Pb) was one of the first metals to be purified, and it has demonstrated its importance to civilization from ancient Roman times to the present. Piping systems constructed by the Romans are still in service; lead roofs installed in the fifteenth century continue to provide protection from water damage. Lead continues in service for such long periods of time because it produces passive films, which build up on the surfaces of pipes and containers and prevents significant corrosion and also avoids consequent lead release to the contents or to the environment. Despite the relatively low mechanical strength and high toxicity of lead, it has endured as a commercial material for many reasons, among them are that lead is an effective shield from radiation, and also is resistant to acids, such as sulfuric, chromic, phosphoric, and others. Safety practices must be precisely followed when fabricating lead products. Lead melts at the relatively low temperature of 327°C (621°F) and boils at 1700°C (3092°F), making fabrication impossible by high-heat-input processes, such as arc welding (with the exception of gas tungsten arc welding). The oxyfuel gas processes, however, are routinely used. When freshly cut, lead surfaces are bright and silvery, but when oxidized, the surfaces change to dull gray. This adds to the complications of welding; however, lead and lead alloys are easily cast and mechanically worked. Zinc (Zn) melts at 419°C (787°F) and has a relatively low boiling point of 907°C (1665°F). Zinc is more readily welded than lead, and more welding processes are available for welding zinc than for welding lead. One reason for this is that zinc is less toxic than lead. Oxyfuel gas welding, arc welding, and resistance welding are all used in the welding of zinc and zinc alloys. Gas metal arc welding is not used on zinc-based alloys because of the excessive spatter and erratic transfer associated with this process. Details of welding and soldering of lead and zinc are presented in this chapter.