Volume 2 Issue 1
Research ArticleApril 01, 2021
Investigation of Premature Failure of Brass Tubes Leaking in a Heat ExchangerUsman Niaz , Mihaiela Minea Isac and Roderick I L Guthrie* Abstract:
Failure investigation of a typical heat exchanger was conducted. The equipment comprised brass tubes (C23000) fitted with an AISI 1020 “turbulator spring” at its center. The heat exchanger developed water leaks during service. Ideally, the heat exchanger has a recommended life of 40,000 hours, but the one in question only lasted 12,000 hours. Treated water at an operating pressure of 64 psi. was circulated through the brass tubes with inlet and outlet temperatures of 47 °C and 57 °C, respectively. On the external surfaces of the tubes, an air/fuel mixture entered the heat exchanger, at a temperature of 75 °C, and left at 52 °C. As such, the heat exchanger was designed to lower the air/fuel mixture’s temperature by 20 °C, before the gaseous mixture entered an engine, for optimum combustion conditions. Scanning Electron Microscope (SEM) and Energy Dispersive Spectroscopic (EDS) analysis revealed that the surface areas of tubes suffering from corrosion, being depleted in zinc versus the bulk zinc content of the alloy; an indication of dezincification. Macroscopic examination of one of the sectioned tubes showed a small pinhole at the surface, approximately 12 mm, from the end of the tube. It exhibited slight bulging, characteristic of thermomechanical damage. The inside adjacent areas showed excessive pitting. Evidence of erosion-corrosion as a result of the combined effect of galvanic induced corrosion, due to material mismatch of the tube and the turbulator spring, coupled with an erosion of the brass tube, by the continuous vibration of the turbulator spring in contact with it, was also observed.