Basically, a Mill Certificate or Mill Test Report provides quality assurance by showing the chemical and physical properties of the stainless steel used in food grade process.
At the mill, when a heat of steel (lot of steel) is being produced, it is tested. The test results are then documented, and a mill certificate is generated for the heat of steel using a heat number. After the steel is processed into sanitary stainless steel fittings, tubing, valves, or even vessels, the heat number will be stamped on the outer surface.
This is so that the heat number can still be tracked using the mill certificates.
Most importantly, the mill certificate will show the basic material type of the sanitary component, SS 304 and SS 316L. The cert will show the range limits of material compositions. The carbon, sulfur, chromium, for example are listed.
Other than material, the mill certificate will show the physical properties, such as yield and tensile strength. The dimensions such as the size and thickness will also be shown.
At NKE Flow, we work hard to try to make sure each piece of sanitary stainless steel valve, tube, and fitting come with its heat number and mill certificate.