Modeling of the Effect of Condensed Water Film Hydrodynamics on Top-of-the-Line Corrosion

Abstract Prediction of Top-of-the-line corrosion (TLC) in wet-gas pipelines relies on the estimation of water condensation rates (WCR) at the top surface of the pipe. WCRs are computed from the calculated cooling temperature profile along the pipe, the gas composition, and the flow rate, which are all used to estimate the chemistry of the condensed water droplets or film and the consequent TLC rate. This approach leads to calculated TLC rates that are maximum at the inlet to the pipeline where the WCR is maximum, followed by decreasing TLC rates as WCRs decrease along the pipeline. However, available field data from several wet gas pipelines show that the top wall loss is not maximum in the first 0.2-1 km of the pipeline, which is inconsistent with the maximum, overly conservative TLC rates predicted by established methods in those areas. Thus, current TLC modeling can lead to significant misjudgment of the performance of carbon steel in design studies. This work introduces a novel modeling approach that estimates the hydrodynamics of the condensed water film and its effect on the predicted TLC rates. The new model can reproduce field behavior and reduces conservatism in TLC prediction.