Analysis on CP Failure of Long-distance Pipeline

A number of CP failures of long-distance pipeline are analyzed. The CP failures are divided into three categories: the first is that of pententiosat, cable, referrence electrod, and CP system; the second is that of isolated flange and external coating; and the third is that of interferrence of AC or DC, bridging with some metal, and that of having been induced by other construction. The different trouble shooting methods are put forward in the paper.