Quick Answer
Quick Answer
To validate chemistry against a grade specification: identify the exact grade, standard, and revision; locate the composition table for that grade; compare every reported element on the MTC against its specified minimum or maximum; flag any element outside the allowed range. Also check that the analysis type (heat vs product) matches the applicable tolerance column.
Overview
Chemical composition validation is a core quality activity in metals procurement and fabricated equipment inspection. When a Mill Test Certificate (MTC) arrives with a heat of steel, the certificate's reported chemistry must be checked against the composition limits defined in the applicable material standard before the material is accepted into the fabrication program.
Despite its apparent simplicity, this check fails in practice for several common reasons:
- Using the wrong grade or edition of the standard
- Not checking all specified elements (omissions on MTCs are non-conformances)
- Confusing heat analysis and product analysis tolerances
- Ignoring customer overlay requirements that are tighter than the base standard
- Accepting an MTC that states the correct grade but does not report all required elements
This page provides a systematic approach to chemistry validation that covers each of these failure modes.
Step 1 — Identify the Exact Grade and Standard
The purchase order or material requisition specifies the governing document. A complete reference looks like:
"ASTM A240 / ASME SA-240, Type 316L, latest edition"
or:
"EN 10088-2: 2014, Grade 1.4404, Condition +A"
Critical details to confirm before opening the composition table:
- Standard number and edition year — composition limits can change between revisions. Use the edition current at the time of order unless the contract specifies otherwise.
- Grade designation — "316" and "316L" have different carbon limits; "S32205" and "S31803" (both called "2205") have different nitrogen minimums.
- Product form — some standards have different limits for plate vs bar vs pipe vs forgings.
- Thickness range — carbon steel grades often have composition limits that vary with product thickness.
Step 2 — Identify the Analysis Type on the MTC
Two types of chemical analysis appear on MTCs:
| Analysis Type | Sample Source | ASTM Tolerances |
|---|---|---|
| Heat (Ladle) Analysis | Ladle sample during melting | Baseline limits in composition table |
| Product Analysis | Sample from finished product | Slightly wider — per ASTM A29 Table 1 or equivalent |
Most MTCs report heat analysis. Product analysis has wider tolerances (typically ±0.01–0.02 % for major elements) because there is natural segregation in a solidified ingot/strand. Do not apply product analysis tolerances when only heat analysis is required, and vice versa.
Step 3 — Build the Comparison Table
For each element specified in the grade's composition table, record:
| Element | Spec Min | Spec Max | MTC Reported | Status |
|---|---|---|---|---|
| C | — | 0.030 % | 0.021 % | PASS |
| Mn | — | 2.00 % | 1.45 % | PASS |
| Si | — | 0.75 % | 0.48 % | PASS |
| P | — | 0.045 % | 0.028 % | PASS |
| S | — | 0.030 % | 0.012 % | PASS |
| Cr | 16.0 % | 18.0 % | 16.8 % | PASS |
| Mo | 2.00 % | 3.00 % | 2.22 % | PASS |
| Ni | 10.0 % | 14.0 % | 10.7 % | PASS |
| N | — | 0.10 % | 0.065 % | PASS |
Example: SS 316L per ASTM A240
Step 4 — Check for Missing Elements
A common non-conformance is an MTC that reports only some elements. Standards require reporting of all elements listed in the applicable composition table (some grades also require reporting residual elements if they are present above trace levels).
For duplex and super duplex grades, nitrogen is a mandatory reported element — its absence on an MTC is a non-conformance even if all other elements are present and within range.
Check: Count the elements in the standard's composition table and verify that the MTC reports a value for each one. "Not detected" or "< 0.001 %" is acceptable for elements with only maximum limits; a blank cell is not.
Step 5 — Apply Customer Overlay Requirements
Customer overlay requirements (also called supplementary requirements or purchase order additions) impose tighter limits than the base standard. Common examples:
- Sulfur ≤ 0.010 % for pharmaceutical or high-polish applications (tighter than ASTM A240's ≤ 0.030 %)
- PREN ≥ 35 minimum for duplex 2205 in offshore service
- Carbon ≤ 0.020 % for some nuclear or pharmaceutical applications
- Ferrite number 3–8 FN in weld deposits (not a base material requirement, but may appear in WPS/PQR requirements)
These requirements must be captured at order placement and checked separately from the base standard. An MTC that passes ASTM A240 can fail a project requirement if a customer overlay was not applied.
Step 6 — Flag and Document Non-Conformances
Any element outside its specified range — whether above a maximum or below a minimum — is a chemistry non-conformance. The correct disposition process:
- Do not accept or process the material pending resolution.
- Issue a non-conformance report (NCR) referencing the specific element, reported value, and specified limit.
- Determine disposition: reject and return to supplier; request additional product analysis; request certified replacement heat; apply for a concession if the deviation is minor and engineering review confirms fitness for service.
- Document the disposition in the project quality record.
Common Chemistry Validation Failure Modes
| Failure Mode | How It Occurs | Prevention |
|---|---|---|
| Wrong standard edition | Using a 2018 table for a 2023 order | Always specify and use the edition cited in the PO |
| Grade confusion (316 vs 316L) | Carbon limit applied is wrong | Check grade designation first, then apply limits |
| Missing elements | MTC does not report N for duplex | Require all elements per standard in purchase order |
| Product vs heat analysis mix-up | Applying heat tolerances to product analysis data | Identify analysis type before checking limits |
| Overlay requirements not checked | Only base standard checked | Maintain a customer requirements register per project |
| Incorrect range direction | Checking a minimum as a maximum | Build a structured comparison table for each MTC |
Automating Chemistry Validation with TestCert
Manual chemistry validation against standards tables is accurate when done carefully, but it is slow and error-prone at scale — especially when multiple grades, multiple standards, and customer overlay requirements must be tracked across hundreds of MTCs in a project.
TestCert automates the process: upload an MTC, identify the grade and applicable standard, and the platform performs the element-by-element comparison automatically, flags non-conformances, and generates a conformance record tied to the heat number and purchase order line. Customer overlay requirements are configured once per project and applied to every MTC reviewed under that project.
Ready to automate your certificate workflow?
Try TestCert freeFrequently Asked Questions
What is the difference between heat analysis and product analysis on an MTC?
Heat analysis is taken from a ladle sample at the time of melting and represents the average composition of the heat. Product analysis is taken from a sample cut from the finished product and may differ slightly from heat analysis due to segregation in the solidified steel. ASTM standards define specific tolerance ranges by which product analysis may deviate from heat analysis limits (per ASTM A29 Table 1 or equivalent). Most MTCs report heat analysis; product analysis is typically performed for dispute resolution or when the customer specifically requires it.
What if an element is reported as 'trace' or 'not detected' on the MTC?
For elements with only a maximum limit (e.g., S ≤ 0.030 %), a "trace" or "< 0.001 %" value is compliant — the actual content is well below the maximum. The non-conformance occurs when the field is blank (no data provided) rather than when it is reported as a low value. For elements with both minimum and maximum limits (e.g., Cr in 316: 16.0–18.0 %), "not detected" would be a failure of the minimum requirement.
Can I accept an MTC if one element is slightly out of range?
Not unilaterally. An out-of-range element is a non-conformance under any ASTM, ASME, or EN standard. The only exceptions are if the applicable standard explicitly provides variance allowances (e.g., product analysis tolerances) that bring the value back into range, or if a formal engineering concession is raised and approved by the responsible quality authority. Accepting out-of-range material without documented disposition is a quality system failure.
How do I verify chemistry for a grade not listed in my usual standards?
For unusual grades or proprietary specifications, the procedure is the same but the reference document changes: (1) obtain the material data sheet or proprietary specification from the supplier; (2) confirm it is the same document referenced on the purchase order; (3) apply the composition table from that document. If the supplier cannot provide the reference specification, that is itself a non-conformance — the MTC must be traceable to a documented standard.