Damages, defects and other substances affecting the surface of stainless steel equipment will occur in the manufacturing process, such as dust, float iron powder or embedded iron, hot tempering color and other oxide layers, rust spots, abrasive burrs, arc initiation marks, welding spatters, flux, welding defects, oil and grease, residual adhesives and paints, chalk and marking ink. Most of them are neglected or not well done because of their harmful effects. However, they have potential hazards to oxidation protective films. Once the protective film is damaged, thinned or otherwise altered, the stainless steel below begins to corrode. Corrosion generally does not spread over the entire surface, but around the defect. This kind of local corrosion is usually pitting corrosion or crevice corrosion. These two kinds of corrosion will develop to depth and breadth, and most of the surface will not be corroded.