Mill test certificates (EN 10204)

The four EN 10204 document types

EN 10204 defines the inspection documents that go with metallic products. It does not say which tests to run — the product standard and the order do that — only who issues the document and what kind of evidence it carries. The current edition is EN 10204:2004. The "mill test certificate" (MTC) a buyer asks for is almost always a 3.1.

Specific inspection means tests on the products being delivered (or on the test unit they come from); non-specific means tests on the same kind of product from the same process, not necessarily these. The 1991 edition's 3.1.A, 3.1.B and 3.1.C have been withdrawn — 3.1.B became 3.1, and 3.1.A and 3.1.C became 3.2.

What a 3.1 certificate should show

• Manufacturer (the mill) and its address, logo and quality-system reference
• Certificate number, date and the edition of EN 10204 it is issued under
• Purchaser and order number, and often the purchaser's own specification
• Product: form, the product standard and grade (e.g. EN 10025-2 S355J2+N), delivery condition
• Dimensions, number of pieces or coils, mass
• Heat (cast) number for each line, and the piece, bundle or coil number that ties the steel to it
• Chemical composition — the ladle (cast) analysis, and the product analysis if the order asked for one; often the carbon equivalent
• Mechanical tests: yield strength, tensile strength, elongation, with the specimen position and direction
• Impact (Charpy) test: the temperature, specimen size and the individual and average energies
• Other tests the standard or order requires: hardness, bend, through-thickness (Z), grain size, non-destructive testing
• Heat-treatment condition and marking
• A statement that the products comply, and the name, position, signature or stamp of the inspection representative

A certificate may cover several heats; each line of product should point to its own heat and results.

How to check a certificate

1. Trace the steel. Find the heat number (and piece or coil number) stencilled, stamped or tagged on the steel and find the same number on the certificate. A certificate you cannot tie to the material in front of you proves nothing about it.
2. Read the right standard. Check that the standard, its edition and the grade on the certificate are what the order asked for, and that the delivery condition matches (+N, +AR, +M, Q&T…).
3. Check the chemistry. Compare every element with the standard's limits for that grade and thickness. Work out the carbon equivalent and compare it with the limit, if one applies — the carbon equivalent calculator does it from the certificate figures.
4. Check the mechanical results. Minimum yield strength usually falls as thickness rises: compare with the value for the actual thickness band. Check tensile strength against both the minimum and the maximum, and elongation against the minimum for the specimen used.
5. Check the impact test. The test temperature has to match the grade (J0 = 0 °C, J2 = −20 °C, and so on) and both the average and the lowest single value have to meet the standard.
6. Check the quantities. Pieces, sizes and weights on the certificate should match the packing list and the bill of lading.
7. Ask the mill. For anything critical, send the certificate number to the mill and ask it to confirm the certificate is genuine. Most mills will.

Red flags

• No heat number, or heat numbers that do not appear on the steel
• A "mill certificate" issued on a trader's or stockist's letterhead instead of the mill's — a 3.1 is issued by the manufacturer
• The same test results, to the last digit, on certificates for different heats or orders
• Results that sit exactly on the standard's limits, or are all round numbers
• Mechanical values that do not fit the chemistry — very high strength from a very lean composition
• A certificate dated before the steel was made, or a standard edition that did not exist on that date
• Grade, thickness or quantity that differ from the order, the packing list or the marking
• Signs of editing: different fonts, misaligned figures, a photocopied stamp, a missing signature
• A 3.2 certificate with no third-party name or signature

A doubtful certificate is a reason to stop and verify before the steel is used — not after it is welded into a structure or a pressure system.

Ordering the right document

• Name the document type in the enquiry and the contract: "inspection certificate 3.1 to EN 10204". If a third party has to witness, say 3.2 and name the inspection company and who pays.
• Ask for any extra tests the standard leaves optional — product analysis, impact tests at a particular temperature, Z-quality, ultrasonic testing — at the time of order. They cannot be added afterwards.
• When steel passes through a stockist, ask for the mill's original 3.1 with the stockist's own transfer document that ties the cut pieces to the original heat.