The tube bundle of the desalination water heat exchanger in the atmospheric and vacuum distillation units of the petrochemical industry is severely corroded
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The image below shows the tube bundle of the hot water heat exchanger in the constant pressure/constant reduced pressure unit 1 of the petrochemical industry. The model is YA500－66－25－4, and the tube bundle material is 10# steel. The operating condition is that the tube side contains condensate, while the shell side contains residue oil ； The operating temperature is 108 degrees in the tube side and 120 degrees in the shell side ； The pressure in the tube side is 0.65 MPa, and that in the shell side is 1.1 MPa. This tube bundle has been in use for over a year; due to the corrosion caused by residue oil and condensed water on its inner and outer walls, its service life is of just over 2 years. The components removed during vacuum distillation are mainly some hydrocarbon compounds with high boiling points, as vacuum distillation is typically used to separate substances with high boiling points that are difficult to separate by normal pressure distillation. The main cause of metal corrosion in five-line systems is the effect of chlorides; sulfides react with the iron ions and water generated by corrosion to form iron sulfide and sulfur dioxide. These substances are more corrosive, can damage stainless steel components, and release toxic substances. Desalinated water may contain low-molecular-weight organic acids (such as formic acid, acetic acid, propionic acid, and butyric acid), which are more corrosive than high-molecular-weight organic acids.
In the vacuum and five-stage desalination heat exchangers used in the petrochemical industry, the tube bundles are often subjected to severe corrosion due to the harsh operating conditions. The main reason is that residue oil and condensed water affect the tube bundle of 10# steel material. Residue contains corrosive substances such as sulfides and chlorides, which react with iron ions to form even more corrosive compounds like iron sulfide and sulfur dioxide. At the same time, the low-molecular-weight organic acids in the demineralized water also caused further corrosion to the tube bundle. Therefore, the service life of the tube bundle is much shorter than expected, requiring special attention to material selection and the maintenance of the tube bundle. .