Failure assessment of composite cooler tubes in a gas boosting station

The present study describes origin and failure mechanisms of air cooled heat exchangers tubes, in a gas pressure boosting station. Hydrocarbon gas was circulating within aluminum finned tubes and cooling was done by forcing ambient air over the exterior of the tubes, made of carbon steel A-214 material. The hydrocarbon gas was contained traces of H2S and substantial level of CO2. The investigation was carried out in a station located in southern part of Iran. The process involved condensation of water and hydrocarbon along the length of tubes, resulting in a wet gas multiphase flow situation. Such type of coolers is also called composite coolers. The failure of tubes was characterized on the bases of all the available evidences and metallurgical examinations, such as analysis of tube materials, feeding gas, condensate water, and the residue inside the tubes. The processing was also simulated by Hysis-3.1 software, in order to evaluate and compare various parameters such as gas flow rate, liquid water and hydrocarbon formation, in actual and design condition. The air cooled tubes showed highest corrosion rate and was experienced leakage regularly. The results indicated that, low velocity assisted sweet corrosion caused severe pitting inside the tubes, and led to failure.