Corrosion of Distribution System Materials in RO and NF Softened Waters: Insights from Static Tests and Dynamic Pilot Loops

Abstract

The increasing use of softened and low-mineral waters produced by reverse osmosis (RO) and nanofiltration (NF) in drinking water supply systems has renewed concerns regarding pipeline corrosion and its implications for water quality and infrastructure durability. This review synthesizes data from static jar tests and dynamic pilot-loop studies to compare the corrosion behaviur of cast iron, ductile iron, steel, galvanized steel, copper, and cement-based materials when exposed to membrane-treated waters. Dynamic loop experiments—still scarce in the literature—are shown to be essential for reproducing realistic hydraulic conditions, dioxygen availability, and long-term scale evolution, yielding corrosion outcomes that differ substantially from those obtained under static conditions. Across all materials, remineralization strategies that restore calcium, alkalinity, and carbonate buffering capacity significantly reduce corrosivity by promoting the formation of protective CaCO₃ and mixed Fe/Ca carbonate layers. Multi-technique analytical approaches (gravimetry, SEM, XRD, FT-IR) provide complementary insights into corrosion products and passivation mechanisms. Remaining challenges include the limited number of long-duration loop studies, the need to assess corrosion inhibitors and hybrid remineralization strategies, and emerging public-health considerations associated with low-nutrient, post-membrane waters. Overall, this review demonstrates that dynamic loop testing is critical for designing effective post-treatment and ensuring the resilience of distribution systems supplied with RO/NF-softened waters.