Causes of External Corrosion on Buried Water Mains

This paper discusses the interim results and conclusions from an AWWA Research Foundation sponsored study, which will determine the causes of and solutions to external corrosion of water pipelines. A companion paper discusses the interim solutions to corrosion on buried water mains. A detailed literature review was conducted that encompasses relevant industries with corrosion control experience. A nation-wide water utility survey was conducted which focused on corrosion and corrosion control which confirmed that the water utility industry has a unique perspective on corrosion and corrosion control as compared to other industries that regularly implement corrosion control. The fundamental mechanisms of corrosion are well known. Corrosion of metals is a well-understood electrochemical process that results in the degradation of a material or its properties by its environment. For buried metals, corrosion is the result of the formation of anodic (corroding) and cathodic (noncorroding) areas of electrically continuous materials in a common electrolyte (soil). The difficulty is that the resulting corrosion damage at the anodic area of the pipe can be similar in appearance for different causal factors. The question is not how corrosion occurs, but more specifically, under what conditions encountered in the water utility industry does corrosion rear its ugly head.