Buyers of fittings and flanges often treat PMI reports, mill test certificates and heat numbers as interchangeable proof that the material is right. They are not. Each answers a different question, and each has limits. Knowing what each one proves — and what it cannot — helps you ask for the right evidence for your service.
Three Kinds of Evidence
| Evidence | What it proves | What it does not prove |
|---|---|---|
| EN 10204 3.1 certificate (MTC) | The heat was tested by the manufacturer and its chemistry and mechanical properties met the stated specification and grade | That a particular part on your site came from that heat — only traceability links the two |
| Heat number traceability | A part marked with a heat number belongs to a documented heat with a certificate | That the marking is correct — marking errors and mix-ups are possible |
| PMI (positive material identification) | The alloy family and main alloying elements of the actual part tested match the expected grade | Mechanical properties, heat treatment, or carbon content with most handheld XRF instruments |
What a Certificate Tells You
An EN 10204 3.1 certificate reports test results for a specific heat or lot — chemistry, tensile and yield strength, elongation, and other tests required by the specification — validated by the manufacturer's independent inspection representative. It is the main evidence that the material meets the standard. Our guide on reading an EN 10204 3.1 certificate explains how to check one.
What Traceability Adds
Traceability is the chain that connects a physical part to its certificate: the heat number marked on the fitting, the same number on the packing list, and the same number on the MTC. Without that chain, a perfect certificate proves nothing about the part in your hand. Check that marking, packing list and certificates agree before material goes into stores.
What PMI Can and Cannot Show
- Can: confirm that a 316L fitting contains molybdenum and is not 304, or that a Cr-Mo part contains chromium and molybdenum in the expected range — on the actual part, at receipt or after installation.
- Can: catch mix-ups, mismarking and wrong-grade substitution before welding.
- Cannot (with handheld XRF): measure carbon, so it cannot distinguish 304 from 304L or 316 from 316L; optical emission (OES) instruments are needed for that.
- Cannot: confirm strength, hardness, heat treatment or grain structure — those come from the certificate and from mechanical tests.
For a practical example of separating grades, see how to identify genuine SS 304L fittings.
Using All Three Together
- Require EN 10204 3.1 (or 3.2) certificates for every heat
- Require heat-number marking on every part, and heat numbers on the packing list
- Specify PMI — sample or 100% — where wrong-grade material would be dangerous, such as alloy steel in high-temperature service or stainless steel in corrosive service
- State whether PMI must detect carbon (OES), and who performs it
Browse our fittings and flanges, or ask about PMI and documentation for your order.
Ask About PMI and Certificates
