Failure investigation of brass heat exchanger tube

Failure analysis was carried out on a brass tube that leaked during service in a heat exchanger. The leaked tube had numerous cracks. The service fluid at the tube side is cooling water, while it is lube oil at the shell side. Microscopic examinations and energy dispersive spectroscopic analyses were carried out on the brass tube to understand the root cause of the failure. Microscopic examination of the tube cross sections revealed that the cracks initiated from the areas that suffered corrosion attack at the internal surface. Chemical analyses indicated that the areas that suffered corrosion attack were depleted in zinc in comparison to the bulk of the alloy. The failure investigation suggested that the brass tube suffered dezincification and the failure of the tube was due to corrosion fatigue that initiated from the areas of dezincification.