The Influence of Soil Chemistry on SCC of Underground Pipelines

Abstract

High-pH stress corrosion cracking (SCC) failures of underground pipelines have occurred in a wide variety of soils, covering a range in color, texture, and pH. No single characteristic has been found to be common to all of the soil samples. Similarly, the compositions of the water extracts from the soils have not shown any more consistency than the physical descriptions of the soils. On several occasions, small quantities of electrolytes have been obtained from beneath disbonded coatings near locations where high-pH stress corrosion cracks were detected. The principle components of the electrolytes were carbonate and bicarbonate ions and it is now recognized that a concentrated carbonate-bicarbonate environment is responsible for this form of cracking. Much of this early research focused on the anions present in the soils and electrolytes. This paper summarizes the results of analyses of soil and electrolyte data in which the relationship between the cations and the occurrence of high-pH and near-neutral pH SCC were evaluated.