Failure analysis on unexpected perforation of heat exchanger tube in methacrylic acid reboiler of specialty chemical plant

Heat exchanger tubes are regarded as a vulnerable component of reboilers due to different working conditions between tube side medium and shell side medium. In this paper, an unexpected perforation failure of heat exchanger tube that occurred in methacrylic acid reboiler of a German world's leading specialty chemical plant was investigated in depth. Macro observation showed that the perforation presented concave appearance both on the inner and outer walls of the failed tube. This was fairly different from the appearance of perforations reported in the past literatures. Comprehensive analysis finally reveled that this unique failure was caused by unreasonable flushing operation of steel water gun with the initial water pressure of 2300 kgf/cm(2). It produced several irregular shallow indentations on the inner wall of a tube at first. Erosion then happened with a shallow impact angle in the indentations where pits were gradually formed. After a period of operation, the selective local erosion was accelerated by the occurrence of vortex erosion on the pits, resulting in perforation failure. Countermeasures were thus put forward to avoid the recurrence of similar failure. Considering that this kind of perforation failure in heat exchanger tubes caused by improper flushing operation is seldom reported in the world, the achievement given by this paper would be very conducive to enhance the safety maintenance management of similar equipment.