How to Specify Stainless Steel in an RFQ: Grade, Size and Testing

Written by: Emma, Technical Sales Engineer  |  Reviewed by: Ethan, Materials Engineer  |  Updated: August 2026

Introduction

A request for quotation that reads "Please quote 316L stainless steel sheet" will produce a quote — but not necessarily for the material the buyer actually needs. Without the standard, dimensions, finish, delivery condition, certification, and inspection requirements, the supplier must guess, and every guess is a potential mismatch that surfaces only at receiving, after the material is paid for and shipped.

This guide explains how to write a stainless steel RFQ that removes that ambiguity. The goal is a specification that a supplier can price accurately and that a receiving inspector can verify: grade + UNS + applicable standard + product form + dimensions + quantity + surface/condition + testing + certification + delivery.

The core idea to keep in mind is that a good RFQ is a definition, not a request for a price. It defines what material is required, how it will be verified, and where and when it must arrive. When those three things are defined, the price that comes back is meaningful; when they are not, the price is a guess that hides the real cost of the mismatch.

1. What Information Should a Stainless Steel RFQ Include?

A complete stainless steel RFQ is a technical-commercial definition of the material, how it will be verified, and where and when it must arrive. The core fields are:

• Grade — the common name (e.g., 316L).
• UNS designation — the unified numbering code (e.g., S31603).
• Applicable standard — the ASTM, EN, or other specification for the product form.
• Product form — plate, sheet, coil, pipe, tube, bar, or fittings.
• Dimensions — the complete size description.
• Quantity — weight or piece count, as applicable.
• Surface finish — 2B, BA, No. 4, No. 1, etc.
• Heat treatment / delivery condition — annealed, solution annealed, etc.
• Testing requirements — standard or supplementary.
• MTC type — EN 10204 3.1 or 3.2, as required.
• PMI / third-party inspection — where required.
• Incoterms and destination — delivery terms and location.
• Required delivery date — when the material is needed.

2. Grade and UNS: Start With the Exact Material

The grade is the starting point, but the common name alone is not enough, because similar names denote different alloys:

• 304 vs 304L — 304L is the low-carbon version, preferred where welding or sensitization resistance matters.
• 316 vs 316L — 316L is the low-carbon version of the molybdenum-bearing 316.
• 2205 vs 2507 — both duplex, but 2507 is super duplex with higher chromium, molybdenum, and nitrogen.

Pairing the grade with its UNS number removes ambiguity. For example, "2205" is commonly S32205, but a buyer should confirm the UNS because a grade name can have more than one associated UNS designation. Never write just "stainless steel" or "316 equivalent" — if a buyer uses an EN designation or another system, the supplier should be asked to confirm the correspondence with the governing standard, rather than assuming every "equivalent grade" is identical in chemistry, mechanical properties, product form, and standard.

The reason this matters is practical: "equivalent" is a claim, not a fact. Two designations from different systems may be "equivalent" for general purposes yet differ in a specific element range or a property limit that matters to a particular application. For example, a low-carbon requirement, a nitrogen addition, or a specific heat-treatment condition may not transfer across designation systems. Confirming the exact UNS and standard closes that gap before an order is placed.

3. Product Standard: Match the Standard to the Product Form

One of the most common RFQ errors is applying a single ASTM number to every product. ASTM standards are product-form specific. A240 governs plate, sheet, and strip; it does not govern pipe or bar. The table below shows typical correspondences:

These are typical correspondences, not universal rules — the specific standard must be confirmed against the product form, grade, and service. The point is that the standard must match the product: an RFQ that pairs "A240" with pipe is asking for a standard that does not govern pipe.

The same discipline applies to other forms. Pipe fittings are typically governed by a different standard (such as A403 for wrought austenitic stainless steel piping fittings), and forgings by a forging standard (such as A182). A buyer who orders "stainless steel to ASTM A240" and receives fittings or forgings has specified the wrong product standard for those forms. Matching the standard to each product form in the RFQ is what makes the inquiry coherent.

4. Size and Tolerance

Each product form has its own size vocabulary, and the buyer should use the correct one:

• Sheet / plate: thickness × width × length.
• Coil: thickness × width, plus coil weight and, where relevant, inner/outer diameter.
• Pipe: NPS or OD × wall thickness (or schedule) × length.
• Tube: OD × wall thickness × length.
• Bar: diameter or section size × length.

Size and tolerance are two different things. A buyer who states a thickness but has a tighter-than-standard tolerance requirement must say so explicitly; otherwise the supplier will quote to the standard tolerance, which may not match the buyer's assumption. If a project has special dimensional tolerance requirements, they belong in the RFQ.

For pipe and tube, also be precise about OD vs NPS (nominal pipe size) and wall thickness vs schedule. NPS is a nominal designation, not a true outside diameter for most sizes, and "schedule" is a wall-thickness convention — a buyer who writes "2-inch pipe" without specifying NPS or OD, schedule or wall, leaves the supplier to guess at one of the most consequential dimensions on the order.

5. Surface Finish and Delivery Condition

Surface finish is a separate field from grade, and it varies by product form. Common finish terms include No. 1, 2B, BA, No. 4, HL, and pickled/passivated finishes, among others. The finish must match the product form and application — a finish that is standard for sheet may not apply to pipe or bar.

Two cautions: first, surface finish does not substitute for grade or corrosion-resistance specification — a polished 304 is still 304. Second, the delivery condition (annealed, solution annealed, or cold worked, as applicable) is also a separate requirement that affects properties and should be stated.

For hygienic or precision applications, the finish may also need a measurable surface-roughness (Ra) value in addition to the finish name. Two sheets can both be "polished" and have different Ra, so where roughness actually matters for the application, state both the finish and the required Ra rather than relying on the name alone. As with tolerance, the finish requirement should be explicit because the supplier will otherwise quote to the standard or common practice, not to the buyer's unstated assumption.

6. Testing, Certification and Inspection

This is where RFQs most often become vague. The buyer should understand the difference between the items that may be requested:

• MTC / mill test certificate — the document recording chemistry, mechanical properties, and standard compliance.
• EN 10204 Type 3.1 — validated by the manufacturer's inspection representative.
• EN 10204 Type 3.2 — additionally validated by the purchaser's or a third-party inspector.
• PMI (positive material identification) — verifying the actual alloy at receipt; not the same thing as an MTC.
• Dimensional inspection — checking size and tolerance.
• Hardness — a property control relevant to many applications.
• Tensile / mechanical testing — confirming strength and ductility.
• IGC testing (e.g., ASTM A262) — intergranular corrosion testing where applicable.
• Charpy impact — where toughness is required.
• ASTM A923 — detecting detrimental intermetallic phases in duplex stainless steels, where applicable.
• NACE-related requirements — for sour service where applicable.

It is essential to distinguish standard-required testing (what the material standard requires), project-required supplementary testing (what the project specification adds), and buyer-requested inspection (such as PMI or third-party witnessing). Not every RFQ needs every test; the RFQ should state explicitly which tests are mandatory and which are supplementary, so the supplier prices them correctly.

A practical way to decide what to request is to ask what the material must prove on arrival. If the concern is identity and mix-up, request PMI. If the concern is independent confirmation of the test results, request EN 10204 Type 3.2. If the concern is a specific failure mechanism — intergranular corrosion, brittle phases in duplex, or sour-service cracking — request the corresponding test (such as A262 for IGC, A923 for duplex, or NACE-related testing). Anchoring each requested test to the concern it addresses keeps the RFQ purposeful rather than a long list of unstated requirements.

7. Example: From a Weak RFQ to a Complete RFQ

Start with the weak version:

This leaves the standard, dimensions, finish, condition, certification, inspection, destination, and delivery date all unspecified. The complete version supplies them:

8. RFQ Checklist

A reusable checklist for a complete stainless steel RFQ:

• Material / Grade
• UNS
• Standard
• Product form
• Dimensions
• Tolerance
• Surface finish
• Heat treatment / condition
• Quantity
• MTC type
• Testing (mandatory vs supplementary)
• Inspection (PMI / TPI)
• Packing
• Incoterm
• Destination
• Required delivery date
• Special requirements

9. Common RFQ Mistakes

• Writing a grade without a UNS. The grade name can be ambiguous.
• Writing "ASTM" without a specific product form. Standards are product-form specific.
• Ignoring dimensional tolerance. Size and tolerance are different requirements.
• Confusing surface finish with material grade. Finish does not change the alloy.
• Not stating MTC 3.1 vs 3.2. The certification level affects cost and lead time.
• Treating PMI as an MTC. They are different verification tools.
• Not marking tests as mandatory or supplementary. Suppliers cannot price unstated requirements.
• Using "equivalent grade" without confirming the standard. Equivalents can differ in chemistry and properties.
• Omitting quantity, destination, and delivery date. Commercial terms are part of the RFQ.
• Treating a supplier's commercial assumptions as technical requirements. Clarify what is stated vs assumed.

Frequently Asked Questions

Q1: What should be included in a stainless steel RFQ?
Grade + UNS, applicable standard, product form, dimensions, tolerance, surface finish, condition, quantity, MTC type, testing, inspection, packing, Incoterm, destination, and delivery date.

Q2: Do I need to specify the UNS number?
It is strongly recommended. A UNS number removes the ambiguity that a grade name alone can leave, especially where a name has more than one associated designation.

Q3: What ASTM standard should I use for stainless steel sheet?
ASTM A240/A240M covers plate, sheet, and strip. Pipe, tube, and bar use different standards, so match the standard to the product form.

Q4: What information is needed for stainless steel pipe?
Grade + UNS, ASTM A312 (for austenitic pipe), NPS or OD, wall thickness or schedule, length, and any finish, testing, or certification requirements.

Q5: What is the difference between MTC 3.1 and 3.2?
A 3.1 certificate is validated by the manufacturer's inspection representative; a 3.2 certificate additionally requires purchaser or independent third-party validation. State which one is required.

Q6: Is PMI required for stainless steel?
Not by default. PMI is a buyer-requested or project-required verification, useful where grade mix-up risk is high. It is not the same as an MTC.

Q7: Should surface finish be included in an RFQ?
Yes, when it matters for the application. The finish is a separate field from the grade and varies by product form.

Q8: How should stainless steel dimensions be written?
Use the product form's vocabulary: thickness × width × length for sheet/plate, OD × wall thickness for tube, NPS × schedule for pipe, and diameter for bar.

Q9: Can I ask suppliers to quote an equivalent grade?
You can, but you should require the supplier to confirm the correspondence with the governing standard. Different designation systems do not always map to identical chemistry, properties, or product forms.

Q10: What information helps suppliers provide an accurate quotation?
A complete technical-commercial definition — grade, UNS, standard, form, dimensions, finish, condition, quantity, certification, testing, Incoterm, destination, and delivery date.