Identifying naphthenic acid corrosion mechanism on heat exchanger unit by computational fluid dynamic simulation

Abstract

Corrosion in refinery assets is complex which involves multi factors contributing to damage mechanisms. The present study aims to evaluate the damage mechanism which caused the heat exchanger (HEX) to leak in parallel sequence. In this sense, experiments were conducted to investigate the correlation between convective heat transfer coefficients and reveals the correlation with material degradation in the heat exchanger. Failure analysis was concluded HEX was attacked by naphthenic acid corrosion (NAC) due to sharp-edged, crater-like holes to sharp-edged streamlined grooves with corrosion product consist of sulphide. Material behaviour analysis assisted by computerized fluid dynamics (CFD) software strongly suggested that the inhibitor is not well distributed at the location of 356 mm because the velocity distribution at the specific location of the corrosive tubes was not uniform. Parallel failure initiated in the distribution of inhibitor and heat in HEX using CFD. From the results of the research, it can be concluded that the selection of material needs to be upgraded to at least 9% molybdate alloying content. CFD results reveal the optimum temperature and pressure of heat exchanger to control NAC attack as well as failure associated with the impact of stream detachment inside the bay to a few tubes. Overall results reveal the CFD method is suitable in predicting the fluid flow and thermal condition at the location of the corrosion failure in the shell tube heat exchanger. The location of corrosion can also be identified and the streamline of flow can be visualized by other materials failure analysis techniques.