In this guide 6 sections
A mill test certificate states the grade, heat number, chemical analysis and mechanical results for a batch of steel. Check that the heat number matches the tags on the bars. The grade must match the drawing, and every value must sit inside the specification limits. Confirm the type is the one your customer asked for.
What the certificate actually proves
The certificate ties a heat of steel to its measured properties. A heat is one melt poured at the mill. Every bar cut from it shares the same chemistry, and the heat number is the thread that links them.
The European standard for these documents sorts them into types. The lowest is a plain declaration of compliance. Next comes a test report with typical values. Above that sits an inspection certificate issued by the mill’s own quality department, and the highest is one countersigned by an independent inspector or the buyer’s representative.
Many drawings and purchase orders name the type. If the order asks for the inspector-verified kind and the stores clerk accepts a mill-issued one, the lot is already non-conforming. Nobody has touched a machine yet.
- Declaration of compliance with no test values
- Test report with typical or non-specific values
- Inspection certificate from the mill’s own department
- Inspection certificate verified by an independent party
The header block: grade, heat code and dimensions
Start at the top. Read the steel designation, the product form, the size, the heat number, the lot or bundle number and the purchase order reference. These six fields must agree with what arrived on the truck.
Walk to the rack with the certificate in hand. Compare the heat number to the paint mark, stamp or tag on the bar ends. A mismatch usually means bars from two heats were bundled together, or a certificate was copied from a different consignment.
Grade names also trip people up. A 20MnCr5 bar and an 8620 bar look alike in the stores yet carry different standards. Match the designation on the certificate to the one on the drawing, and note any equivalent your engineer has approved in writing.
Chemistry and mechanical values against the specification
Chemistry comes as a table of elements. Carbon, manganese, silicon, phosphorus, sulphur, chromium, nickel and molybdenum are the usual columns. Compare each against the minimum and maximum in the material standard, not against last month’s certificate.
Mechanical results sit lower down. Look at yield strength, tensile strength, elongation, and where relevant impact energy and hardness. Check the units. A value in megapascals read as another unit has passed bad steel before.
Some drawings add limits beyond the standard, such as low sulphur for machinability or a hardenability band for case-hardened gears. Write these extra limits on the incoming inspection sheet so the clerk sees them.
- Each element inside the stated minimum and maximum
- Yield, tensile and elongation in the right units
- Impact or hardness values where the drawing asks
- Heat treatment condition shown, such as annealed or normalised
- Extra customer limits beyond the standard
Signs a certificate has been altered or copied
Look at the paper itself. Mixed fonts deserve a phone call to the supplier. So do a row with different alignment, a stamp sitting over the numbers and a missing mill logo.
Chemistry that is identical to the last decimal across two heats is suspicious. Real melts drift. Another warning is a certificate dated after the delivery note.
Do not reject on a hunch. Ask the supplier for the mill’s original, and for high-risk parts such as pressure fittings or load-bearing shafts, send a sample for spectrometer checking at an outside lab.
Keeping certificates linked to the parts you ship
Reading the certificate is half the job. The other half is remembering it. When a customer asks which heat went into the shafts shipped in March, a folder of scanned PDFs sorted by date will not answer quickly.
Record the heat number against the goods receipt, then carry it onto each work order that consumes that bar. The finished lot then points back to the certificate. Software that stores the scan, the heat number and the work order together turns a day of searching into a lookup.
Start this week. Pick the last ten certificates received and check whether you can name the finished lots made from each one.
Incoming mill certificate check sheet
Single page, three blocks. The header block has rows for certificate type, designation, heat number, lot number, size and purchase order. The values block has columns for each element and mechanical property, with specification minimum, maximum, certificate value and a tick-or-cross cell. The sign-off block records the bar-end tag check, the inspector’s initials and the rack location.
Open a blank worksheet to printQuestions owners ask
Who should check the mill test certificate?
The person who receives the steel should check the header block against the tags. A quality engineer should check the values against the specification. Two sets of eyes catch more than one.
What if the heat number is missing from the bar?
Quarantine the bar. Ask the supplier to identify the heat in writing, or cut a sample and test it. Do not issue it to a job that needs traceability.
Do we need a certificate for every delivery?
Check your drawings and customer contracts. Safety-related parts usually need one per heat. Commodity parts may need only a declaration. Write the rule down so stores follows it.
How long should certificates be kept?
Follow the retention period in your customer agreement or industry standard. Where none is stated, keep them for the full warranty period on the parts you supplied.