A comparative analysis of perforation and blister features on internally corroded aged water pipeline wall

Abstract

Despite well-controlled chlorination, no known operational outages and physicochemical parameters of the water indicating a slight tendency to form carbonate deposits, aged and internally uncoated pipelines may experience unexpected internal corrosion events that raise integrity concerns. A typical corrosion damage was investigated consisting of a single perforation covered by a corrosion product cap (CPC) approximately 5 cm in diameter and surrounded by a relatively dense population of blisters of approx. 1 cm in diameter covering shallow corrosion pits. It was observed on the inner wall of an aged on-land water distribution pipeline after decades of corrosion-free operation. A dense population of bacteria, sulphides and extracellular polysaccharide substances were detected in the CPC, but none at the pit bottom surrounding the perforation and within the blisters, but abundant fungi were observed on scanning electron microscopy images of the blister bottom. The morphology of the blisters suggests that the blister formation is due to the loss of adhesion of the corrosion product layer, which is influenced by the formation of spherulitic crystals. The Fourier transform infra-red spectroscopy results suggest that the growth of these carbonate crystals is related to the adsorption of microbially generated carbonyl groups. The results support a likely scenario of the effect of biomineralization on the appearance of corrosion through the formation of blisters, which may provide a niche for microbes that eventually cause corrosion damage.