Mill Certificate Sample: What to Check

A mill certificate sample (also called mill test certificate or MTC) is the quality document that accompanies every shipment of piping materials from the producing mill. Reviewing a mill certificate correctly requires checking specific fields against the purchase order and the applicable material specification. This article walks through the key fields found on a typical mill certificate and explains what to verify in each section.

The format of mill certificates varies between manufacturers, but the required content is standardized by EN 10204 and the applicable material specification (ASTM, API, or EN).

Mill Certificate Sample: Field-by-Field Checklist

Field	What It Shows	What to Verify
Certificate number	Unique document reference	Record for traceability; cross-reference with packing list
EN 10204 type	Certificate classification	Must match PO requirement (typically 3.1 or 3.2)
Manufacturer	Producing mill name and address	Must be on the approved manufacturer list (AML)
Customer/PO reference	Buyer’s purchase order number	Must match your project PO
Material specification	Standard and grade	Must match PO exactly (e.g., ASTM A106 Gr. B, not Gr. A)
Product description	Type, process, dimensions	Seamless/welded, OD, wall thickness, length
Heat number	Steel melt identifier	Must match physical marking on the product
Lot/batch number	Group of items from same heat and treatment	Links multiple items to the same test results
Chemical composition	Actual element percentages	Every element within specification limits
Mechanical properties	Tensile, yield, elongation, hardness	Meet or exceed minimum values
Impact test results	Charpy V-notch energy values	If specified, must meet minimum energy at test temperature
Heat treatment	Thermal processing condition	Must match standard requirement
NDE results	Hydrotest, UT, RT results	Pass/fail per applicable code
Authorized signature	QC representative stamp and signature	Document is invalid without it
TPI signature	Third-party inspector (3.2 only)	Required only for EN 10204 Type 3.2

Sample Chemical Composition Check (ASTM A106 Gr. B)

Element	ASTM A106 Gr. B Max (%)	Sample MTC Value (%)	Status
Carbon (C)	0.30	0.19	Pass
Manganese (Mn)	0.29-1.06	0.88	Pass
Phosphorus (P)	0.035	0.012	Pass
Sulfur (S)	0.035	0.005	Pass
Silicon (Si)	0.10 min	0.25	Pass
Chromium (Cr)	0.40	0.08	Pass
Molybdenum (Mo)	0.15	0.03	Pass

Common Mistake

Accepting a mill certificate without verifying the heat number on the physical product. The certificate may be genuine, but if the heat number does not match the marking on the pipe, fitting, or flange, the traceability chain is broken. Always perform a physical heat number check during receiving inspection.

Key Points

• A mill certificate is only valid when signed by the manufacturer’s authorized QC representative (and by TPI for Type 3.2).
• Verify chemical and mechanical values against the actual ASTM/EN specification limits, not against previous certificates or approximate memory.
• Every field on the mill certificate should match the purchase order and the applicable standard. Any discrepancy is grounds for a non-conformance report (NCR).

Read the full guide to mill test certificates