Influence of scale prevention on corrosion of heat-transfer tube

The pH-control method usually used in the latest distillation plants has been found unsuitable because of its corrosiveness. In the cases of the pH-control tests, the corrosion rate of a heat-transfer tube was three times or more than that of the untreated operation. An intermittent acid treatment developed recently in our laboratory was also tested, and resulted in the same amount of corrosion as the pH-control method. These results were electrochemically studied tracing the change in the polarization curves of the tube. As a result of these experiments, it was concluded that an extremely low oxygen concentration under 3 ppb must be required to keep down the corrosion rate when using the acid treatments.