Failure Analysis of CO Shift Gas Heat Exchanger Tubes

Tubes of a heat exchanger in a chemical plant leaked frequently, and such tubes will be replaced in one or two years. Therefore, it is necessary to find the leak causes and put in place preventive measures. In this paper, analysis methods such as macroscopic examination, the chemical composition test, metallurgical structure analysis, scanning electron microscopy (SEM) observation, energy spectrum (EDS) and X-ray diffraction (XRD) analysis of corrosion products and condensate water analysis are described that were conducted to analyze the leak causes of the heat exchanger tubes. After analyzing operating parameters (temperature, pressure) and the structure of the bottom area of the heat exchanger, it was found that the heat exchanger tubes inlet was operating in the vapor dew point zone. The results indicate that process parameters (temperature, pressure) were not properly selected and there were substantial SO42- in the process of production. As a result of that dew point corrosion in the form of pitting corrosion and stress corrosion cracking (SCC) which caused the leak occurred on heat exchanger tubes. Finally, relevant preventive measures were recommended according to the analysis results.