A CASE FOR INSTALLING AN ANODE WITH EVERY REPAIR OF A CAST IRON WATER MAIN

摘要

The repair of a cast iron water main presents an opportunity to install a sacrificial anode, which can reduce the rate of corrosion and thus potentially delay the occurrence of future failures within the anode’s zone of influence. While the additional cost of the anode is small, is it a good economic investment? Using the spatial location of failures, cluster analysis identifies zones of active corrosion defined as four or more failures, each no more than 20m from its nearest neighbour within the cluster. Within these clusters, a failure is considered to have occurred within a cathodically protected zone if the failure occurred within 20 m. of a previously installed anode. Otherwise, the failure is considered to have occurred within a zone that is not protected. Survival analysis shows that the times to failure within cathodically protected zones are longer than the times to failure in an unprotected zone. An economic analysis shows that the incremental costs of sacrificial anodes indeed result in an economic benefit based on the deferral of future failures and their associated costs alone. The subsequent delay in replacement of the main represents a further economic benefit.