Post-perforation external corrosion of cast iron pressurised water mains

Abstract

The corroded external surfaces of older cast iron water mains buried in soils for many decades usually show a rough undulating topography. Sometimes, there also are areas of relatively smooth topography similar to uniform corrosion but over undulating surfaces. Investigations show this pattern is associated with localised pipe-wall perforation and sometimes pipe fracture. It is proposed that corrosion pitting from the outside surface of the pipe perforates the pipe-wall, allowing fresh oxygenated drinking water from inside the pipe to effuse through the orifice. This then causes a high rate of localised general corrosion under the graphitised layer. The resulting thinning of the pipe-wall may then lead to pipe fracture under high water pressure.

Empirical models for long-term localised corrosion of cast iron pipes buried in soils

“…Corrosion penetrations or pits have very little influence on the stress state in a pipe wall. In some research, it has been assumed that larger deep areas of corrosion loss develop, but how this is likely to occur has only recently been given some attention [18]. In essence, the through wall perforation allows fresh, oxygenated, perhaps chlorinated water from inside the pipe to escape under pressure and thus corrode a wider, local region on the outside of the remaining pipe wall and under the graphitised layer.…”

A reinterpretation of the Romanoff NBS data for corrosion of steels in soils

“…Of major practical interest, however, is not the early corrosion behaviour but rather the longer-term progression of corrosion (over years, decades), particularly in soils such as those in which practical ferrous pipes might be buried, noting that any protective coatings seldom last long and that particularly for what are now heritage systems, cathodic protection was not applied [2,6]. The statistical variability in the amount of corrosion and of pit depth also is of much practical interest [5,7,[12][13][14], since for practical applications such as water supply systems the probability of pipeline perforation and hence the probability of failure is important. However, before estimates of statistical uncertainty are applied, it is necessary to have a good understanding of the mean-value progression of corrosion and pit depth.…”

Microbiologically influenced corrosion: a review of the studies conducted on buried pipelines

“…Specifically, long-term corrosion of pipelines involves a step-wise lateral growth of localized corrosion pit depth (Soltani Asadi and Melchers 2017b). This has been explored further to include the effect of water leakage after pipeline perforation due to pit growth (Melchers 2017). Soils that allow for easy drainages, such as sandy soils which have large particles and thus large pores, are less corrosive than those who tend to collect and hold water, such as clay with its tiny pores (Escalante 1989).…”