Mill Test Certificate Fields Explained (All Sections)

No two mills format their MTCs identically, but every compliant certificate covers the same core data set. This page defines each field, explains its purpose, and flags what to look for when verifying a certificate. Use it alongside the reading guide for practical verification.

Quick Answer

A mill test certificate is structured into four main sections: identification (heat number, grade, dimensions, PO reference), chemical composition (actual elemental percentages vs specification limits), mechanical properties (tensile, yield, elongation, impact, hardness test results), and a certification statement signed by the authorised inspector.

Section 1: Document Header and Certificate Identification

Mill / Manufacturer Name

The legal name and address of the producing mill. This should match the name of the manufacturer, not a trading entity. For certifications under EN 10204, the manufacturer is responsible for the accuracy of all stated data.

Certificate Number

A unique alphanumeric reference assigned by the mill. This number is used to retrieve the original record from the mill's quality management system. Request this reference when disputing or verifying a certificate.

Certificate Type

The document type under the applicable standard — typically EN 10204 Type 2.2, 3.1, or 3.2. If the certificate does not explicitly state the type, it should be treated as a non-specific test report at most.

Date of Issue

The date the certificate was generated. For new material, this should be close to the production date. A certificate dated years before delivery, or one that appears reused across multiple deliveries, requires investigation.

Purchase Order / Order Reference

The buyer's PO number and/or the mill's own works order number. This links the certificate to a specific commercial transaction.

Section 2: Material Identification Fields

Heat Number (Cast Number)

The single most important identifier on an MTC. A heat number (also called cast number in some regions) identifies the discrete batch of metal produced in one furnace charge. All material cut from a single heat shares the same chemical composition as measured by the ladle analysis.

The heat number must match the marking stamped, stencilled, or laser-etched on the physical material. See What Is a Heat Number? for a full explanation.

Product Form

Defines the physical form of the product: seamless pipe, welded pipe, hot-rolled plate, cold-drawn bar, forging, fitting, structural section, coil, etc. Test results from one product form do not apply to another, even for the same grade and heat.

Grade / Specification

The material designation and the standard it conforms to:

ASTM designation: A106, A516, A333, A182, etc., followed by the grade (Gr. A, B, C, 60, 65, 70, F316L)
EN designation: S235, S355, P265GH, 316L, etc., with the delivery condition suffix
API designation: 5L, PSL1/PSL2, X52, X65, etc.

The grade on the certificate must match the grade ordered exactly, including all supplementary requirements.

Dimensions

The nominal dimensions of the product:

Plate: thickness × width × length (mm or inches)
Pipe: outside diameter × wall thickness × length (or schedule)
Bar: diameter and length
Fitting: nominal pipe size and schedule

Dimensions confirm that the certificate applies to the product physically received, not a different size or thickness range that might have different specification requirements.

Quantity / Weight

Number of pieces and/or total weight or length supplied. Used to reconcile the certificate against the delivery note.

Section 3: Chemical Composition

The chemical composition table is the core of the MTC. It lists each chemical element present in the material, the actual measured value, and the specification limit.

Common Elements and Why They Matter

Carbon (C) — Primary strengthening element in carbon steel. Higher carbon increases strength but reduces weldability and toughness. Maximum carbon content is tightly controlled in weldable structural and pressure grades.

Manganese (Mn) — Increases strength and hardenability. Typically 0.5–1.6% in structural steels. Controlled to prevent manganese banding and sulphide precipitation.

Silicon (Si) — Deoxidiser and mild strength contributor. Usually 0.1–0.5% in killed steels.

Phosphorus (P) — Embrittling element. Maximum typically 0.025–0.035% in structural grades; lower in sour service grades (≤0.020%).

Sulphur (S) — Embrittling element, particularly at elevated temperatures. Also promotes hydrogen-induced cracking (HIC) in sour service. Maximum typically 0.015–0.030%; HIC-resistant grades: ≤0.003%.

Chromium (Cr) — Corrosion resistance (stainless steels ≥10.5% Cr) and high-temperature strength (Cr-Mo alloy steels).

Molybdenum (Mo) — High-temperature creep strength and corrosion resistance (316/316L stainless, 1.25Cr-0.5Mo, P91).

Nickel (Ni) — Low-temperature toughness (9% Ni cryogenic steel) and austenite stabiliser in stainless.

Carbon Equivalent (CE) — A calculated value that predicts weldability. Not an element, but derived from the chemical analysis using the IIW formula or the Pcm formula for low-carbon steels. High CE values require preheat before welding.

Analysis Type

MTCs may report:

Ladle analysis (heat analysis): Sample from the molten bath — most common
Product analysis: Sample taken from the finished product — tighter control but less common

The analysis type should be stated. Most specifications accept ladle analysis.

Section 4: Mechanical Properties

Tensile Test Results

Tensile Strength (Rm / UTS) The maximum engineering stress the material can sustain before fracture. Expressed in MPa (N/mm²) or ksi. Most specifications set a minimum; some also set a maximum upper bound.

Yield Strength (ReH, ReL, Rp0.2)

ReH: upper yield point (used for carbon and low-alloy steels that exhibit a distinct yield point)
ReL: lower yield point
Rp0.2: 0.2% proof stress (used for austenitic stainless steels and materials without a distinct yield point)

Must meet specification minimum.

Elongation (A5 or A50) The percentage elongation of a gauge length after fracture — a measure of ductility. A5 uses a gauge length of 5× the sample diameter; A50 uses 50 mm. Specification minima vary widely (10–40%) depending on grade and form. Higher elongation = more ductile.

Reduction of Area (Z) Percentage reduction of the cross-sectional area at the fracture point. Used alongside elongation as a ductility indicator, more common in through-thickness (Z) quality plates.

Impact Testing (Charpy V-Notch)

Charpy impact test results indicate toughness at a specified temperature. The test strikes a notched specimen with a pendulum; the energy absorbed (in Joules) is recorded.

Fields to check:

Test temperature (e.g., −40°C, −20°C, 0°C, room temperature)
Average energy (mean of three specimens — must meet specification average minimum)
Individual values (each specimen — must meet specification single-value minimum, typically 70% of the average)
Orientation (longitudinal or transverse — transverse values are lower and are the more conservative requirement)

Hardness

Expressed in:

HBW (Brinell): most common for structural and pressure steels
HV (Vickers): used in heat-affected zone testing and NACE-controlled applications
HRC (Rockwell C): sometimes used for high-strength or hardened steels

For sour service (NACE MR0175 / ISO 15156), maximum hardness limits apply to prevent sulphide stress cracking. A single value above the limit is grounds for rejection.

Section 5: Heat Treatment

Records the thermal or thermomechanical processing applied:

As-rolled (AR)
Normalised (N): air cooled from above upper critical temperature
Normalised and Tempered (NT)
Quenched and Tempered (QT): rapid quench, then tempered at lower temperature
Thermomechanically Controlled Process (TMCP)
Solution Annealed (SA): for stainless and alloy steels, then quenched

The stated condition must match the purchase order specification.

Section 6: Supplementary Tests and Examination Results

Depending on specification and PO requirements:

Hydrostatic test — test pressure and result (pass/fail)
Non-destructive examination — UT, RT, MT, PT reference and acceptance criteria met
NACE / HIC test results — crack length ratio, crack thickness ratio, crack sensitivity ratio
Grain size (ASTM grain size number, particularly for fine-grain killed steels)
Delta ferrite content (for duplex and austenitic stainless welds)

Section 7: Certification Statement and Signatories

The certification block declares:

That the supplied material conforms to the referenced standard and purchase order
The name, title, and signature of the authorised inspector
For EN 10204 3.2: the name, company, and signature of the independent inspector
The date of signing

The signature must be original or a verifiable electronic equivalent.

Frequently Asked Questions

What is the difference between A5 and A50 elongation?

Both measure ductility. A5 uses a gauge length of 5× the specimen's original diameter; A50 uses a fixed 50 mm gauge length. Values are not directly comparable between methods. The test method is specified in the applicable standard and should be stated on the MTC.

Why do some MTCs show multiple rows in the mechanical properties table?

Multiple rows indicate testing was performed on specimens from different positions (longitudinal vs transverse), different thicknesses (if the specification has thickness bands), or different heats included in the delivery. Each row relates to a distinct test piece.

What does 'killed steel' mean on an MTC?

Killed steel has been fully deoxidised — typically with silicon and/or aluminium additions — before casting. This results in a more uniform structure and consistent properties. Fine-grain killed steel has additional alloying (Al, Nb, V) to achieve a refined grain size, which improves low-temperature toughness. Killed steel is required for most pressure and structural applications.

Why is the carbon equivalent important for welding?

The CE determines the preheat temperature required before welding to prevent hydrogen-assisted cold cracking in the heat-affected zone. High CE (above about 0.42%) requires preheat; very high CE (above 0.55%) requires extensive preheat and post-weld heat treatment. The MTC's chemical data allows the welder to calculate this.

Can I extract MTC field data automatically?

Yes. AI-based extraction tools (such as those in TestCert) can parse PDFs and scanned MTCs, identify and extract individual fields, and compare them against specification limits — reducing manual data entry and the risk of human verification errors.

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