Coking and corrosion of the tube bundle in the heating water heat exchanger of the constant and reduced pressure units in petrochemical industries
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The image below shows the tube bundle of the heating water heat exchanger in the atmospheric and vacuum distillation unit of the petrochemical industry. Model: YB800-175-16/16-4, Material: 10# steel. This tube bundle has been in operation for nearly two years. Operating conditions: Shell side: minus four lines, temperature 181°C, pressure 0.65 MPa. Pipeline: Medium, heating water; temperature 95°C, pressure 0.65 MPa. During maintenance, when the heat exchanger was opened, it was found that there was a large amount of scale in the tube side; some tubes were already blocked and severely coked, with corrosion present in the metal. Corrosion has occurred on the external heat exchange tubes of the shell side.
In the atmospheric and vacuum distillation units of the petrochemical industry, the heat exchanger tubes operate under high temperature and pressure conditions; especially due to the interaction between the reduced-pressure stream and the heating water, coking and corrosion tend to occur. Coking may be caused by the following reasons: 1. The composition of the reducing four-line may not match the temperature and flow rate conditions inside the tube, leading to the formation of deposits. 2. Temperature differences within the pipe section and unstable flow conditions increase the risk of coking. Corrosion can be caused by the following factors: 1. Moisture or impurities in the medium lead to electrochemical corrosion. 2. Material 10# steel has insufficient corrosion resistance in high-temperature environments with corrosive media. 3. Thermal stress and metal fatigue caused by large temperature differences exacerbate pipeline corrosion. To address this situation, it is recommended to regularly clean and inspect the heat exchangers, improve the flow conditions in the pipelines, and consider using more corrosion-resistant materials in order to extend the service life of the equipment. .