November 2, 2026 · Stainless Steel
Stainless Steel Mill Test Certificate: How to Verify It Before You Pay
A stainless steel mill test certificate proves nothing until the heat number on the paper matches the number stenciled on the plate. Do that one check, read the nickel figure against the standard, and you catch most of the 201 sold as 304 before the container leaves the port. The rest of the check takes twenty minutes and one handheld gun.
What an EN 10204 Certificate Actually Is
EN 10204:2004 lists four document types. Only two of them carry test results, and only one is signed by somebody outside the production department.
| Type | Name | What is in it | Who signs |
|---|---|---|---|
| 2.1 | Declaration of compliance | Statement that the goods meet the order. No test values. | Manufacturer |
| 2.2 | Test report | Non-specific inspection results, may come from the production lot. | Manufacturer |
| 3.1 | Inspection certificate | Results for the heats actually delivered, traceable to heat number. | Manufacturer and an inspection representative independent of production |
| 3.2 | Inspection certificate, third party | Same as 3.1, plus witnessed and signed by the buyer's or an independent inspector. | Manufacturer plus independent inspector (SGS, BV, TUV, Intertek) |
Most Chinese mills issue 3.1 for export by default, and it costs you nothing extra. So if a supplier offers 2.1 and calls it a mill test certificate, ask why. Usually it means the material came from a trader, not straight from a mill.
Write the requirement on the purchase order. "MTC" alone gets you a 2.1 about half the time, and then you find out at customs or at your customer's incoming inspection, which is the worst possible place.
Five Things That Must Be on the Certificate
A 3.1 certificate without these five items is not a 3.1 certificate. I check them in this order.
- Heat number, per item. One line per heat actually shipped. If the order has three heats and the certificate has one line, the document was not written for your goods.
- Chemical composition from the mill's own analysis. Not "typical values", not a table copied from a standard. Ladle analysis with the actual percentages.
- Mechanical properties. Tensile strength, yield strength (Rp0.2 or Rp1.0), elongation. For ASTM A240 material: 304 minimum 515 MPa tensile, 205 MPa yield, 40% elongation; 316L minimum 485 MPa tensile, 170 MPa yield, 40% elongation.
- Product standard and grade, written out. ASTM A240 / A240M or EN 10088-2, plus the grade and its European number (304 = 1.4301, 316L = 1.4404). "SUS304" alone tells you the mill used a Japanese trade name, not which standard it tested to.
- Signature and stamp of the inspection representative. A name, a role, and a date. If the only signature is the sales office, the document has no inspection value under EN 10204.
How to Read the Chemistry Numbers
These are the ranges in ASTM A240 and EN 10088-2. Read nickel first, chromium second, molybdenum third. That order catches almost everything.
| Grade | Cr % | Ni % | Mo % | C max % | Mn % |
|---|---|---|---|---|---|
| 304 / 1.4301 | 18.0-20.0 | 8.0-10.5 | - | 0.08 | 2.00 |
| 304L / 1.4307 | 18.0-20.0 | 8.0-12.0 | - | 0.030 | 2.00 |
| 316L / 1.4404 | 16.0-18.0 | 10.0-14.0 | 2.00-3.00 | 0.030 | 2.00 |
| 201 | 16.0-18.0 | 3.5-5.5 | - | 0.15 | 5.5-7.5 |
| 430 | 16.0-18.0 | 0.75 | - | 0.12 | 1.00 |
Nickel is the price. It is also the easiest element to get wrong when somebody substitutes. 304 sits between 8 and 10.5% nickel. If a certificate says 304 and the nickel reads 4.2%, the metal is 201 and no stamp on the paper changes that.
Manganese is the other tell. 201 carries 5.5-7.5% manganese because the nickel is replaced with manganese and nitrogen. Any "304" certificate showing manganese above 3% deserves a phone call before the container is loaded.
How Fake 304 Gets Through
I have seen these on real shipments, listed roughly by how often they appear.
- Nickel below 8% with the grade written as 304. The most common one by far. Either 201 with a copied header, or 304 made with a leaner charge.
- One certificate for several heat numbers. Fine if each heat gets its own line. Not fine when a single line covers 20 tonnes that came from four different heats.
- Suspiciously round numbers. Real ladle analyses scatter: 18.12 Cr, 8.04 Ni, 0.041 C. When every heat reads 18.0 / 8.0 / 0.05, the table was typed from a template.
- Carbon that does not match the grade. A 304L certificate showing 0.06% carbon is a 304 certificate with the L added. Under 0.030% is the whole point of the grade.
- Mechanicals missing or out of range. If tensile and yield are absent, the mill did not test, whatever the type number says.
- Heat number not stenciled, or ground off. Some suppliers grind the stencil off seconds or a coil end to hide a substitution. A plate with no heat number cannot be traced to any certificate.
A 20-tonne container of 201 sold as 304 is a five-figure loss at 2026 price levels, because 201 usually trades 25-35% below 304. That gap is why the substitution keeps happening, and why the certificate check is worth twenty minutes.
PMI: What the Gun Proves and What It Does Not
Positive material identification is the arrival check. Two methods, and buyers mix them up constantly.
| Method | Reads | Cannot do | Time per spot |
|---|---|---|---|
| XRF (handheld) | Cr, Ni, Mo, Mn, Ti, Nb and other elements heavier than magnesium | Read carbon, so 304 vs 304L and 316 vs 316L look identical | 5-15 seconds |
| OES (spark, portable or lab) | Carbon, nitrogen and all alloying elements down to hundredths of a percent | Work through mill scale or film, or on a curved narrow edge without preparation | 30-60 seconds |
For most importers XRF is enough. It separates 304 from 201 in five seconds because 8% nickel against 4% is a gap no calibration error can hide. It also catches 316 without molybdenum.
Where XRF is not enough: when your weld procedure names 304L specifically, or when the part goes into a pressure application. Then ask for OES, or send a coupon to a lab. The lab result costs less than re-doing a weld procedure.
What the Verification Costs
Four line items, and only one of them is usually paid by the buyer.
- The mill's 3.1 certificate: free with the goods. No mill charges extra for a document it issues every day.
- Third-party witnessing (3.2): billed per inspector man-day, typically a few hundred USD plus travel in some markets. Also covers dimensional and visual checks while the inspector is there.
- PMI on arrival: the cheapest part. Many fabricators already own a handheld XRF, and service labs charge per spot for the ones who do not.
- Lab chemistry or mechanical test: per sample, with a few days of turnaround. Worth it once, on the first order from a new mill.
Put these in the inspection budget instead of treating them as overhead. On a 20-tonne order a witnessed inspection normally comes in well under 1% of the goods value, and one rejected container costs more than a year of inspecting.
What Ships With Our Stainless Steel
Every stainless order we load goes out with the same four things, whether or not the buyer asks.
- A 3.1 certificate per heat, scanned and sent as a PDF before packing, then a signed paper copy in the document tube with the packing list.
- The heat number stenciled on each plate and printed on the packing list against the item it belongs to.
- Photos of the stencil and the certificate together, taken at the warehouse, for orders where the buyer wants proof before the balance is released.
- Optional third-party inspection arranged before loading. We book the inspector, you pick the company.
That last point matters more than it sounds. If an inspector arrives after the container is sealed, all he can verify is the paperwork. Grades we stock and finish options are on the stainless steel sheet and plate page.
Buyer Checklist Before You Release Payment
Print this, or copy it into your PO notes. It is the same list I run before we send documents out.
- Certificate type is written on the PO as EN 10204 3.1, not "MTC".
- Heat number on the certificate matches the stencil on the plate, item by item.
- Nickel, chromium and molybdenum are inside the range for the ordered grade.
- Manganese is under 2% on any 304 or 316 order.
- Carbon matches the grade, including the L suffix if you ordered 304L or 316L.
- Tensile, yield and elongation are present with real values.
- Product standard and grade are both named, with the European number where relevant.
- Signature and stamp of an inspection representative, plus a date that fits the production window.
- PMI booked for arrival, or a mill sample sent to a lab for the first order.
If any line fails, hold the balance and ask for the heat number again. A mill that has the right paperwork can produce it in an hour. A trader who substituted cannot, and that is the whole answer.
Send us the certificate you received and we will read it with you before you commit. That is a normal request for us, and it is cheaper than a rejected container. Reach us through the contact page, or see the full range on the stainless steel product page.
Reference standards: EN 10204:2004 (metallic products, types of inspection documents), ASTM A240/A240M (chromium and chromium-nickel stainless steel plate, sheet and strip), EN 10088-2 (stainless steels, technical delivery conditions for sheet and plate). Chemistry ranges and mechanical minimums above follow those standards. Price spreads between 201 and 304 are indicative for the 2026 market and move with nickel and mill lead times.
Frequently Asked Questions
Is a mill test certificate the same as a certificate of conformity?
No. A certificate of conformity is normally an EN 10204 type 2.1 document: the mill states the goods meet the order, without test results. A type 3.1 certificate carries the actual chemical and mechanical results for each heat, signed by an inspection representative who does not report to the production department. If your purchase order just says MTC, you will usually get a 2.1. Write EN 10204 3.1 on the PO.
Can a supplier fake an EN 10204 3.1 certificate?
Yes. Blank and filled-in templates circulate, and PDF editing is easy. That is why the paper is only half the check. Match the heat number on the certificate to the number stenciled on the plate, compare the nickel and chromium figures against the standard for that grade, and PMI the material when it lands. A fake certificate usually fails on the heat number match or on nickel.
What is the difference between 304 and 304L on a certificate?
Carbon. 304 allows up to 0.08% carbon, 304L allows 0.030%. Nickel range is also wider on 304L (8.0-12.0% against 8.0-10.5%). For thin sheet under 3 mm the difference matters little in service, but for welded sections over 6 mm the L grade is what keeps carbide precipitation out of the heat affected zone. XRF cannot read carbon, so it cannot tell the two apart.
Does PMI testing damage the stainless steel?
XRF does not touch the surface in any meaningful way, and it is the usual arrival check. Spark OES leaves a small burn mark a few tenths of a millimetre across, so you test an edge or an area that gets cut off. Both methods are done on a clean, scale-free surface. Mill scale or a protective film gives a false reading, so wipe the spot first.
Do I need a 3.1 certificate for 201 or 430?
It depends on the end use, not on the grade. For decorative panels or kitchen trim, a 2.1 statement plus your own PMI is often enough. For food contact, pressure parts, or anything with a weld procedure that names the grade, ask for 3.1 and keep the heat number on file. The material we supply and the documents that go with it are listed on the stainless steel page.
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