Causes Analysis of Inner Wall Corrosion of Wall Reheater Pipe and Preventive Measures

Corrosion and perforation occurred in a wall reheater pipe of a 300MW subcritical coal-fired unit in a power plant. The corrosion causes were analyzed by means of macroscopic examination, X-ray fluorescence spectroscopy, metallographic examination, scanning electron microscopy and energy dispersive spectroscopy. The results showed that when the unit was out of operation, a small amount of condensed water remained at the bottoms of the wall-through elbow and horizontal section duo to the boiler structure and improper boiler shutdown protection, resulting in dissolved oxygen corrosion of the inner wall of the pipe and eventual corrosion perforation. In view of the above incident, a power generation group investigated the units within the area, and proposed a series of preventive measures from the aspects of furnace shutdown operation processes, shutdown protection methods, water vapor quality control, daily maintenance and other aspects.