Abstract: A flash tank filter leaked. The cause of leakage was analyzed by macroscopic observation, chemical composition analysis, scanning electron microscopy and energy spectrum analysis, metallographic examination and other methods. The results show that there were casting defects in the inner wall of the filter. Under the action of internal corrosion medium, pitting corrosion occurred at the casting defects, and then cavitation occured at the outlet section of the flash tank filter, which caused the filter to leak through perforation.