How Heat-Number
Traceability Works.

A heat number is a unique identifier the mill assigns to a single melt — a "heat" — of steel. Everything poured from that melt shares chemistry and mechanical properties, and the heat number is stamped onto the material so it can always be traced back to its origin.

• The MTR is the material's birth certificate. The Mill Test Report (also called a mill certificate or MTC) lists the heat number alongside the chemical composition, mechanical test results and the standards the material meets. Match the stamp on the steel to the heat number on the MTR, and you have proven what the material is.
• EN 10204 classifies the certificate. The European standard defines certificate types — 2.1 and 2.2 are declarations and non-specific reports, while 3.1 gives actual test results for that specific material, validated by an inspection representative independent of production. Type 3.1 is the common baseline for structural, pressure and pipeline work; 3.2 adds a purchaser or third-party countersignature.
• Goods-in is the first checkpoint. When material arrives, someone confirms the heat number marked on it matches the certificate — the moment the chain of custody formally begins.

Here is the step that quietly defeats most traceability systems. The moment a plate or pipe is cut, the piece that carries the original stamp and the offcut that doesn't are now two pieces — and only one of them still shows its heat number.

• The heat number must be transferred before the mark is lost. When cutting removes or separates the original marking, the heat number has to be re-marked onto every resulting piece so each stays identified. Do it before the original stamp is gone, not after.
• The offcut carries the same heat. A remnant returned to the rack still belongs to its parent heat — but if it goes back unlabeled, its traceability is gone the instant it leaves the bench. This is one of the most common traceability non-conformances in fabrication.
• It needs to be recorded, not just marked. The transfer is documented — often witnessed by QC per the project quality plan — so there is a paper trail showing that piece B came from heat X via parent piece A.

A shop that nails everything else but loses the transfer step at the saw has a chain with a hole in exactly the place auditors look first.

Complete traceability means the heat number rides all the way up from raw material to the joint it ends up in, joined by everything else that touched the weld. Under ISO 3834 and EN 1090, a traceable weld links to:

• The material — the heat number and its MTR, carried through every cut.
• The procedure — the WPS it was welded to, and the WPQR behind that procedure.
• The consumables — filler metals traced by their own batch and certificate.
• The person — the qualified welder who made it, and their current qualification.
• The result — the inspection and acceptance record for that joint.

Traceability accumulates upward: heat numbers on base-material leaves propagate through the assemblies built from them, so a finished piece carries the full provenance of everything welded into it. That is what lets a shop answer, for any joint, "prove this weld is sound and prove what it's made of" — in one pull, not a week in the archive.

On paper, this chain is fragile at every joint between steps — and the failure is almost never the mill certificate. It is the transfer that wasn't recorded, the remnant that went back unlabeled, the weld log that lives in a different binder from the material log.

• Links break silently. A missing transfer record doesn't raise an alarm; it just becomes a gap discovered under audit pressure.
• Reconstruction is expensive. When the thread is lost, someone spends days rebuilding it from scattered records — if it can be rebuilt at all.
• Software keeps the links live. Capture the heat number once at goods-in, tie it to its MTR, carry it through each cut, and attach it to the joints built from that material — and the chain stays whole by construction, not by heroics at audit time.