Heat Number Traceability in MTCs

Heat number traceability is the system that links every piping component back to the original steel melt (heat) from which it was produced. The heat number is a unique identifier assigned by the steel mill to each individual melt of steel, and it appears on the mill test certificate (MTC) alongside the chemical composition and mechanical test results for that specific heat. In oil and gas piping, heat number traceability in MTCs is a mandatory quality requirement that enables full material verification from raw steel to installed component.

Heat Number Traceability Requirements

Requirement	Details
Heat number source	Assigned by the steel mill at the time of melting
Appears on	MTC, product marking (stencil/stamp), packing list, material receiving report
Traceability chain	Steel heat → billet/slab → pipe/fitting/flange → installed component
ASTM/ASME requirement	Mandatory marking per ASTM A530 (pipes), ASTM A961 (flanges), ASTM A960 (fittings)
EN requirement	Mandatory per EN 10204 for Type 3.1 and 3.2 certificates
ASME B31.3	Requires material traceability for all pressure components
NACE MR0175/ISO 15156	Heat-level traceability mandatory for sour service materials
Typical format	Alphanumeric code (e.g., H7842, 2024-A561)
Transfer marking	Required when original marking is removed during cutting or fabrication

Key Points About Heat Number Traceability

Why heat numbers matter: A single steel heat produces a batch of material with uniform chemical composition. The heat number connects the MTC data (chemistry, mechanicals, heat treatment) to every product made from that heat. If a quality issue arises in service, the heat number allows the operator to identify and inspect all components from the same melt, preventing systemic failures.

MTC verification: During pipe inspection, inspectors verify that the heat number marked on the physical product matches the heat number on the MTC. Any mismatch indicates a traceability break and must be resolved before the material is accepted. For carbon steel pipes, the heat number is typically stenciled on the pipe body along with the specification, grade, size, and manufacturer’s name.

Transfer marking: When a pipe or fitting is cut, machined, or otherwise processed such that the original heat number marking is removed, the fabricator must transfer the heat number to the new piece before removing the original marking. This is called transfer marking and must be witnessed by a QC inspector per the project’s quality plan.

Multiple heats in one order: A purchase order for pipes or fittings may be supplied from multiple heats. Each heat must have its own MTC, and the packing list must reference which items correspond to which heat numbers. Mixing items from different heats on a single MTC without clear identification is a non-conformance.

Pro Tip

During material receiving at site, always cross-reference three documents: the packing list, the MTC, and the physical marking on the product. All three must show the same heat number. This three-way verification is the most effective way to catch traceability errors before materials enter the fabrication process.

Read the full guide to mill test certificates