Hygienic Pipe Fittings: What are Mill Certificates

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.

Heat number on Sanitary Stainless Steel Tube

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.

Types of Certificates (EN10204)

1. 2.1: Declaration of compliance by the manufacturer, no actual test done

2. 2.2: Based on non-specific tests, limited testing done

3. 3.1: Provides actual test results that are validated by the manufacturer

4. 3.2: Provides actual test results that are further verified by an independent third party inspector

Hygienic Pipe Fittings

1. Material certificate type: Hygienic fittings usually come with 2.2 or 3.1 certificates

2. Key details:

   1. Chemical composition (SS 304 or SS 316L)

   2. Physical properties

   3. Heat number traceability

   4. Gasket material of unions

   
   

Hygienic Tubes

1. Material certificate type: Hygienic tubes usually require 3.1 or 3.2 certificates

2. Key details:

   1. Chemical composition (SS 304 or SS 316L)

   2. Physical properties

   3. Surface finish

   4. Heat number traceability

   5. Hydro testing

   6. Welded or seamless

      
      

Hygienic Valve

1. Material certificate type: Hygienic valves usually require 3.1 or 3.2 certificates

2. Key details:

   1. Chemical composition (SS 304 or SS 316L)

   2. Physical properties

   3. Heat number traceability

   4. Seat material

   
   

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At NKE Flow, we work hard to try to make sure each piece of hygienic pipe, fittings, and valves come with its heat number and mill certificate.