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Reading a rebar mill test certificate before you pay
The mill test certificate is the only document that tells you what is inside a bundle of steel. Here is what to check, line by line, before the documents go to the bank.
A cargo of reinforcing bar arrives with a stack of paper, and most of it is about the ship. One document is about the steel itself: the mill test certificate, issued by the mill for each heat of steel it rolled. If it is wrong, incomplete or does not match the tags on the bundles, nothing else in the document set will protect you.
Start with the heat numbers
Every bundle carries a tag with a heat number, the identifier of the batch of molten steel it came from. The certificate should list the same heat numbers, with the tonnage rolled from each. Before anything else, reconcile the two: tags photographed at loading against the certificate, and the certificate against the packing list. A heat number on a tag that does not appear on any certificate is a bundle with no test record.
Chemistry and carbon equivalent
The chemical analysis shows carbon, manganese, silicon, sulphur, phosphorus and the residual elements. For weldable grades, the number that matters most is the carbon equivalent value. Under BS 4449 the limit for the cast analysis is around 0.50 per cent; a higher figure means the bars are harder to weld on site and may crack. Sulphur and phosphorus should sit comfortably under their limits, not on them.
Mechanical properties
For B500B bar to BS 4449, check that:
- the yield strength is at least 500 MPa;
- the ratio of tensile strength to yield strength is at least 1.08;
- the elongation at maximum force is at least 5 per cent;
- bend or rebend tests are reported as passed.
ASTM A615 Grade 60 uses different limits, including a minimum yield of 420 MPa and a minimum tensile strength of 620 MPa. Make sure the certificate tests against the standard in your contract, not the one the mill happens to use at home.
When something does not match
Missing heats, figures exactly on a limit across every heat, or a certificate issued before the steel was rolled are reasons to pause. Ask for a re-test of samples cut from the cargo by the inspection company at the load port. It costs days, not weeks, and it is far cheaper than rejecting steel on a construction site.
On our steel desk, certificates are checked against tags and the contract standard before the cargo leaves the load port, and the inspection report goes into the document set with them.
