Certificate of Compliance vs MTC

A certificate of compliance (CoC) is a document in which the manufacturer declares that the supplied material conforms to the requirements of the purchase order and applicable standard, without providing specific test data. A mill test certificate (MTC), classified as EN 10204 Type 3.1 or 3.2, reports actual chemical and mechanical test results from the producing mill. The distinction between a certificate of compliance vs MTC is critical for procurement engineers specifying inspection documentation for piping materials.

When Each Certificate Type Is Used

A certificate of compliance is acceptable for non-critical, low-risk components where individual test data is not required by the design code. Typical applications include standard gaskets, commercial-grade bolting, pipe supports, and non-pressure-bearing accessories. An MTC is mandatory for all pressure-containing piping components (pipes, fittings, flanges, valves) in oil and gas projects governed by ASME B31.3 or B31.1.

Project specifications often elevate the certificate requirement above the code minimum. For example, a project may require Type 3.1 MTCs for all bolting, even when the design code would accept a simple declaration of compliance.

Certificate of Compliance vs MTC Specifications

Feature	Certificate of Compliance (CoC)	Mill Test Certificate (MTC)
EN 10204 type	Type 2.1 (Declaration of Compliance)	Type 3.1 or 3.2
Test data included	No specific test results	Full chemical and mechanical data
Heat number	Not always included	Mandatory
Traceability	Limited (lot/batch level)	Full (heat number to product)
Issuing party	Manufacturer	Manufacturer (3.1) or manufacturer + third party (3.2)
Typical piping use	Gaskets, supports, non-pressure items	Pipes, fittings, flanges, valves
Acceptance by ASME B31.3	Non-pressure items only	Required for pressure components
Cost impact	Lower (no individual testing)	Higher (specific testing required)
Verification level	Statement of conformity only	Verifiable against ASTM/EN limits

Pro Tip

Never downgrade an MTC requirement to a certificate of compliance to save costs or accelerate delivery. The cost difference is marginal compared to the risk of installing non-conforming material in a pressure system. If a supplier offers only a CoC for a component that requires an MTC per the pipe class specification, reject the offer or require re-testing by an accredited laboratory.

For a complete overview of EN 10204 inspection document types and their application to piping materials, including Type 3.2 requirements for critical and sour service, refer to the detailed guide below.

Read the full guide to mill test certificates