Corrosion rate evaluation and residual life prediction of steel water transmission pipelines

This work presents a corrosion rate assessment and residual life prediction of an in-service steel water transmission pipeline. The case study concerns a DN1400 pipeline, 33 km long, with a nominal wall thickness of 8.8 mm along most of its route. While the external surface remains effectively protected by coating and impressed current cathodic protection, the original internal coating degraded early in service and no longer prevents corrosion by the transported water. The analysis considered two internal corrosion mechanisms: generalized corrosion caused by dissolved oxygen in water, and localized corrosion associated with macrocell effects such as differential aeration and under-deposit attack. Corrosion rates were estimated from key operating and water-quality parameters, including dissolved oxygen, temperature, flow velocity, and electrical conductivity. Two complementary approaches were applied: a Monte Carlo simulation based on probabilistic input distributions, and a deterministic combinatorial method considering all possible parameter combinations. Both methods produced consistent results. Generalized corrosion was estimated at approximately 0.06 mm/year on average, with maximum values below 0.1 mm/year, while localized corrosion ranged between 0.30 and 0.45 mm/year under realistic scenarios. The model was calibrated against documented corrosion failures in drain pipe spools, enabling a preliminary estimate of pipeline residual service life.