The order and making inspection can prevent and find the free iron, ASTM standard A380[3] defines rust test to check the surface of stainless steel iron or steel particles. When asked to absolutely can not have iron, should use the method of inspection. If the results are satisfactory, the application of clean water or nitric acid washing on the surface, until the dark blue completely disappeared. As A380[3] pointed out if rust test solution can not be completely clean out, is not recommended in the process on the surface of equipment, is used to test this method of using direct contact surface of production for human consumption. Test method for simple is exposed to 12~24 hours in water, check whether there is rust. The test sensitivity is poor, and time-consuming. These are the test, not cleaning method. If found to have iron, chemical and electrochemical methods must be used after the introduction of the cleaning.