Effect of Cathodic Protection Conditions on the Stress Corrosion Cracking of Line Pipe Steels

Abstract

Stress corrosion cracking (SCC) of buried line pipe steel was studied from practical aspects of view including cathodic protection conditions. The results obtained are summarized as follows:
1) The most probable occurrence of SCC on buried steel pipelines was thought to be limited to the sites of cathodic disbonding accompanied by corrosion rusts.
2) Cathodic protection current of not less than 1 mA/cm² could cause cathodic disbonding of protective coating on a steel pipe, and could form a sufficient concentration of alkali to produce carbonate-bicarbonate SCC.
3) The more predominant environment to produce SCC on a buried line pipe steel was thought not a caustic alkali solution but a carbonate-bicarbonate solution because of a high partial pressure of CO₂ in the soil.
4) Those pipelines which were cathodically protected at the polarization potential between-1 000 and-1 350 mV vs. Cu-CuSO₄ and at the cathodic current density of less than 1 mA/cm² were thought free from SCC.