Failure analysis of a rapid quench boiler for ethylene cracker

The corrosion and leakage issues of rapid quench boilers have become increasingly prominent in ethylene plants, significantly disrupting the regular functioning of equipment. In pursuit of a more efficacious corrosion protection strategy, a study was conducted on the heat exchange tubes experiencing corrosion leakage in the quenching boiler of a petrochemical company. By means of macroscopic observation, chemical composition analysis, mechanical property analysis, metallographic analysis, fracture surface morphology observation, and energy spectrum analysis, combined with on-site process parameters, a comprehensive analysis of the failure causes of the corroded leakage sites was conducted. It was concluded that the perforation of the heat exchange tubes was caused by high-temperature oxygen corrosion and oxidation induced by scale accumulation, and reasonable countermeasures were proposed. According to X-ray diffraction analysis (XRD), it was found that the scale mainly consisted of Fe₂O₃ and Fe₃O₄, and the scale formation time was relatively long. It is speculated that the accumulation of scale is caused by the rust from the upstream equipment pipelines of the boiler water being carried into the quenching boiler with the fluid flow and accumulating at this location. Regarding the heat exchange tubes, the primary causes of failure are high-temperature oxygen corrosion and oxidation. To verify whether the relevant reactions can occur spontaneously, the critical transition temperature of the reactions is calculated using the free entropy function method. The calculated critical temperature for the occurrence of high-temperature oxygen corrosion and oxidation in the heat exchange tubes under failure conditions is determined to be $$ 1058 K ~ 785 °C. Therefore, under the conditions of heat exchange tube failure, high-temperature oxygen corrosion and oxidation can occur spontaneously.