Bulging and Cracking Analysis of Fuel Gas Heat Exchanger Tubes

Much bulging and cracking phenomenon was found on the tube bundles of a fuel gas heat exchanger during operation process. Means such as macro examination, micro examination, chemical compositions analysis, metallographic analysis and scanning electron microscope analysis were used to analyze the bulging and cracking reason. The results show that the existence of pressure fluctuation in the tube, non-uniform wall thickness of the tube, high H2S concentration of the shell pass medium and more inclusions in the tube material were all reasons for the bulging and cracking of the heat exchanger tube bundles. Stress concentration formed easily at the thinner wall thickness positions of the tube, which aggravated the H2S corrosion at these positions and reduced the wall thickness further. When the wall thickness was reduced to a certain value, bulges were formed under the action of pressure fluctuation. Then cracks were formed at the bulging position and leakage happened with the aggravation of corrosion and continous action of pressure fluctuation.