Industry quality standards require materials to be tested at the manufacturer and the results of these tests be submitted through a report, also called a Mill Sheet, Mill Certificate or Mill Test Certificate (MTC). The only way to trace a steel plate back to its Mill Sheet is the Heat Number. A heat number is similar to a lot number, which is used to identify production runs of any other product for quality control purposes.
Usually, but not universally, the numbers indicate:
- the first digit corresponds to the furnace number
- the second digit indicates the year in which the material was melted
- the last three (and sometimes four) indicate the melt number.
- Example like 74277, the "7" indicated furnace number, "4" indicated Years of Melted Metals, and The last three is Melt number