Investigation on corrosion mechanism and mechanical degradation of corroded cast iron pipes

Abstract

Buried cast iron pipelines are vulnerable to soil-induced localized corrosion, resulting in brittle fracture failure. It is therefore essential to understand how corrosion damage induces mechanical property degradation. However, the differences in localized corrosion characteristics and fracture-sensitive degradation between natural soil (NS) and composition-matched simulated soil solution (SSS) remain unclear. In this paper, HT200 cast iron specimens were exposed to NS and SSS at pH 3.0, 5.0, and 7.0 for 60, 120, and 180 days. Measurements of corrosion rate, pit depth, pitting factor, SEM/XRD, ultimate tensile strength (UTS), and fracture toughness (K IC ) are combined to evaluate corrosion mechanisms and mechanical property degradation. The results show that lower pH accelerates corrosion in both environments, while NS promotes stronger localized corrosion, deeper pits, and higher PF values than SSS. UTS degradation is mainly associated with average metal loss, whereas K IC is more sensitive to pit-induced stress concentration and microcrack accumulation. The novelty of the paper is the establishment of an interpretable NS-SSS correlation model for mechanical property degradation, providing a quantitative basis for its application to degradation assessment and failure evaluation of cast iron pipelines buried in soils.