Pitting corrosion can occur on the outer wall of the tube bundle in the atmospheric and vacuum distillation, roof removal, and fourth-stage heat exchangers used in the petrochemical industry
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The image below shows the heat exchanger tube bundle of the atmospheric and vacuum distillation – top removal and fourth line heat exchanger in the petrochemical industry. Under normal operating conditions, crude oil flows through the tube side, while the fourth line flows through the shell side； The operating temperature is 173 degrees in the tube side and 307 degrees in the shell side ； The pressure in the tube side is 0.52 MPa, and that in the shell side is 0.66 MPa. The tube bundle material is 10# steel. This tube bundle has been in use for over 2 years, and the shell side has developed numerous pitting defects. Refracted fraction 4 is the fourth distillate obtained from the lower part of the vacuum tower; it has a high boiling point because it contains the heavier components of crude oil, which is why refracted fraction 4 possesses a high boiling point. Corrosion by naphthenic acids occurs under such conditions.
Under operating conditions, ring acid corrosion is likely to occur because the reduced tetralin contains heavier components and a higher boiling point. This type of corrosion, which occurs at high temperatures and results in pitting, is mainly caused by the formation of tiny pits as a result of the reaction between the steel and the corrosive medium. Steel 10# has weak resistance to such corrosion; as a result, multiple pitting defects appeared in the shell side. To reduce this corrosion, considering the use of more corrosion-resistant materials or enhancing the anti-corrosion treatment of the shell side could be an option. .