Predicting Internal Corrosion Rates in Wet and Dry Gas Pipelines

A model is developed for predicting internal corrosion rates in pipelines that carry wet or dry natural gas. A significant difference in corrosion between the two types of gas pipelines is that for dry gas, a stagnant layer due to water condensation may be sitting at the pipe surface. The thin solution layer can quickly go saturated and a precipitate film forms to reduce the corrosion rate. For wet gas, water may be constantly present on the pipe surface and the bulk solution chemistry may not change significantly over time. By coupling mass transport, chemical and electrochemical reactions, film growth and the displacement of the metal-solution interface due to metal dissolution, this model is developed based on fundamental principles and allow for predicting the change of solution chemistry, the effect of precipitate film and the steel corrosion rate over time under various operating conditions, including temperature, pressure and gas quality. The model results and its practical implications will be reported and discussed. This work has been supported by the U.S. PHMSA under Contract: DTPH56-08-T-000003.