Failure analysis on abnormal leakage of shell and tube heat exchanger in specialty chemical plant

The shell and tube heat exchanger has been widely used in the chemical industry. However, because of complex operating conditions, the heat exchanger tubes sometimes are leaked. This paper conducted in-depth failure analysis on abnormal leakage of several tubes of a shell and tube heat exchanger, which had been used for nine years in a methyl methacrylate production facility. In order to find out the root cause of the failure, chemical analysis, metallographic structure inspection and morphology observation of the leakage tubes were carried out. The composition and properties of the tube scales were analyzed by X-ray fluorescence spectroscopic analysis (XRF), X-ray diffraction analysis (XRD), thermogravimetric analysis (TGA), and energy spectrum analysis (EDS). The micro-zone features of the leaked tubes were observed with three-dimensional stereo microscope (3D-SM) and scanning electron microscope (SEM). According to the testing results and the actual operating conditions of the heat exchanger, the root cause of abnormal leakage of the tubes was finally determined. The key finding was that the terephthalic acid gas was suddenly desublimated into solid particles while its temperature was about 300 degrees C. Thus, the gas containing terephthalic acid particles caused erosion wear, abrasive wear and local corrosion onto the inlet side of the heat exchanger, leading to abnormal leakage of the tubes. Finally, some suggestions were put forward for the heat exchanger, which were also conducive to the safe operation and failure prevention of similar equipment.