On any surface, free iron rusts and corrodes the stainless steel. Therefore, it must be cleared. Floating powder can generally be removed with dust. Some adhesion is very strong and must be treated as embedded iron. In addition to dust, there are many sources of surface iron, including cleaning with ordinary carbon steel wire brushes and shot blasting with sand, glass beads or other abrasives previously used on plain carbon steel, low alloy steel or cast iron parts, or The aforementioned non-stainless steel products are ground near stainless steel parts and equipment. Wire ropes, spreaders and iron on the work surface can easily embed or smear the surface if the stainless steel is not protected during the blanking or lifting process. Ordering requirements and post-production inspections prevent and detect the presence of free iron. ASTM Standard A380  specifies the rust test method for the inspection of iron or steel particles on stainless steel surfaces. This test should be used when there is absolutely no iron available. If the results are satisfactory, wash the surface with clean pure water or nitric acid until the dark blue color completely disappears. As indicated in Standard A380 , if the rust test solution cannot be completely removed, it is not recommended to use this test method on the process surface of the equipment, ie the direct contact surface used to produce human consumables. A relatively simple test method is to expose the water for 12 to 24 hours to check for rust spots. This test is poorly sensitive and time consuming. These are test tests, not cleanup methods. If iron is found to exist, it must be cleaned by chemical and electrochemical methods described later.