What Is a Heat Number in Steel?
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Talk to our experts- Heat number (steel)
- A heat number is the identifier a steel mill gives to a heat, one batch of steel from the furnace and ladle. It is stamped on the steel made from that heat and printed on the mill test report, so anyone holding a bar, plate or coil can trace it back to that heat's chemical composition and test results.
How it works
Steel is identified and analyzed by heat. ASTM A615, the specification for carbon steel reinforcing bars, requires samples rolled from properly identified heats and a heat analysis showing that the steel meets the required carbon, manganese, phosphorus and sulfur content. Specimens must also pass tensile tests for tensile strength, yield strength and elongation.
Those results go on the mill test report, which names the heat number it represents.
Paperwork is counted per heat, not per order. South Carolina DOT requires every rebar shipment to arrive with the manufacturer's mill test report for each heat included in the delivery. The heat number also decides what happens when a test fails: if a check sample fails, the heat it represents is not to be used in the work.
How a heat number follows steel from the mill to the job
Samples are rolled from properly identified heats, and a heat analysis checks carbon, manganese, phosphorus and sulfur.
The report names the producer, the heat number and size, the grade and the tensile results.
Heat numbers are listed by order number, bar mark, size and grade so each heat can be identified at the destination.
Each shipment arrives with the mill test report for each heat included in the delivery.
What travels with the heat number
South Carolina DOT lists what a rebar mill test report must include:
- Producer information: the mill that made the steel.
- Heat number and size: of the rebar the report represents.
- Grade: the grade for which the steel qualifies.
- Tensile results: yield strength, tensile strength and elongation.
- Origin statement: that the steel was melted and manufactured in the United States.
North Carolina DOT adds a fabricator's form, M&T Form 913, that itemizes heat numbers by bar list or order number, bar mark, size, grade, weight and mill, so each heat number may be positively identified and separated at the destination. The fabricator certifies that no other heat numbers were incorporated in the shipment.
Example
A steel distributor ships a bridge contractor 2 sizes of rebar. The #4 bars come from 2 heats and the #5 bars from 1 heat. That is 2 + 1 = 3 heats on the truck, so the delivery needs 3 mill test reports, one per heat, not one for the order.
If a sample from one #4 heat fails and one of its two check samples fails too, South Carolina DOT's rule is that the heat is not to be used in the work. Finding those bundles fast depends on records that show which bundles came from which heat.
On Shopify
Shopify tracks product quantities by variant and, if you use multiple locations, by location. Heat numbers and their reports are custom data: metafields extend products, customers and orders with your own fields, and a File metafield holds a generic file under 20 MB that renders as a downloadable link in themes.
A common pattern is to record which heat shipped on which order in the ERP or warehouse system, where stock is received and picked, and have an integration write it to the Shopify order.
How Uncap helps
Uncap's guide to what steel buyers expect with every order describes the build: on Shopify, attaching the mill test report for each heat on a delivery to that order, so the contractor and the inspector can pull it from order history, is built during implementation, and each order records which heat it ships from. It is built from your ERP data, and the ERP stays the system of record.
Sources
Frequently asked questions
What is the material heat number in an MTC?
It is the heat number printed on the mill test report, identifying the heat the report covers. South Carolina DOT, for example, requires a rebar mill test report to show the heat number and size of rebar represented by the report.
How do you read a heat number?
Read it off the steel or its tag and match it to the heat number on the mill test report. Then check the grade, size and tensile results on that report against what the order called for.
