Most quotations that come back wrong were wrong on paper, not in the mill. The grade was left as a general description. The standard was named without a designation. The testing requirement was assumed rather than stated. Each of those gaps is an invitation for a supplier to make a reasonable assumption — and their reasonable assumption and yours may not be the same thing.
This is a checklist for writing a pipe material specification that a supplier can quote without guessing. It works for stainless steel and for nickel alloy alike. Nothing here is company-specific; it is the set of fields that determine whether two quotations are actually comparable.
1. Name the specification, not just the family
“316L stainless steel pipe” is not a specification. It is a description, and it leaves open which document the chemical composition and mechanical properties come from, which heat treatment applies, and which supplementary requirements are included. In the ASME system the specification carries all of that.
For austenitic stainless steel pipe, the specification is SA-312/SA-312M. For ferritic-austenitic (duplex) tubing, it is SA-789/SA-789M. For forged flanges, fittings and valves, it is SA-182/SA-182M. These are not interchangeable, and specifying the wrong one is the single most common specification error we see.
| What you are buying | ASME specification | Typical grades |
|---|---|---|
| Austenitic stainless steel pipe | SA-312/SA-312M | TP304L, TP316L, TP316H, TP321, TP347H |
| Duplex stainless steel tubing | SA-789/SA-789M | S31803, S32205 |
| Forged flanges and fittings | SA-182/SA-182M | F304L, F316L, F51, F53, F55 |
| Nickel-chromium-iron alloy pipe | SB-167 | Alloy 600, 690 |
| Ni-Cr-Mo seamless pipe and tube | SB-444 | Alloy 625, 825 |
| Ni-Cr-Mo-W alloy pipe | SB-637 | Alloy C-22 |
A common trap: stainless steel pipe is SA-312, not SA-316. The A316 and A304 designations are the ASTM form of the grade, widely used in commercial language; the ASME specification carrying them for pipe is SA-312. Using the ASTM designation alone means the supplier decides which document governs, and different documents resolve unspecified details differently.
2. State the grade designation and the UNS number
Give both. They are not redundant — the grade designation is the commercial shorthand and the UNS number is the unambiguous identifier, and requiring both removes any room for a supplier to substitute a near neighbour. Verified UNS designations for the grades above:
| Specification | Grade | UNS | Cr (%) | Ni (%) | Mo (%) |
|---|---|---|---|---|---|
| SA-312 | TP316L | S31603 | 16.0–18.0 | 10.0–14.0 | 2.00–3.00 |
| SA-312 | TP316H | S31609 | 16.0–18.0 | 10.0–14.0 | 2.00–3.00 |
| SA-312 | TP321 | S32100 | 17.0–19.0 | 9.0–12.0 | — |
| SA-789 | S31803 | S31803 | 21.0–23.0 | 4.5–6.5 | 2.5–3.5 |
| SA-789 | S32205 | S32205 | 22.0–23.0 | 4.5–6.5 | 3.0–3.5 |
Note the column order in the SA-312 table above: chromium before nickel. In the SA-789 and SA-182 tables the order reverses, with nickel first. This is worth internalising not because you will read chemistry tables all day, but because it is exactly the kind of detail that gets transcribed incorrectly somewhere in a long supply chain — and a 316L with the chromium and nickel swapped is not a valid material.
If your service condition is chloride, seawater or sour, state it. PREN is useful but not sufficient on its own — resistance to chloride stress corrosion cracking is not the same property as resistance to pitting, and a grade selected on pitting resistance alone can be the wrong answer for a chloride service.
3. Give dimensions completely
Nominal size, wall thickness or schedule, and length — plus any tolerance requirement. If you mean a specific wall thickness rather than a schedule, say so and state whether negative tolerance applies. Wall, size and length tolerances are dimensional requirements governed by the relevant dimensional standard, not by the material specification, so they must be written into the order separately.
4. State the testing, don’t imply it
Hydrostatic or eddy current testing, whether each is required, and any supplementary requirements you need on the test report. For corrosion-critical service, consider explicitly requiring the material to be supplied in the solution-annealed and pickled or passivated condition, rather than assuming the delivered condition is suitable. If the pipe will be cut and welded on site, state the delivery condition you need so the supplier can confirm the procedure qualification is achievable from that starting point.
5. Specify the certification you need
Say which certification standard and which type. EN 10204 3.1 and 3.2 are not interchangeable: 3.1 is an inspection document issued by the manufacturer, while 3.2 involves independent inspection by a third party. If your project requires 3.2 and the order does not say so, the default is 3.1. Name the standard, the type, and any language requirement.
6. Close the substitution door explicitly
If the grade is not to be substituted, say that. This is the field most often left open, and it is the one that causes the most expensive disputes. State it in terms a supplier cannot reasonably read another way: whether equivalents are acceptable, and if so, whether the substitution requires prior written approval with a chemistry and mechanical property comparison attached.
A compact checklist
| Field | Example entry |
|---|---|
| Specification | SA-312/SA-312M |
| Grade / UNS | TP316L / UNS S31603 — no substitution |
| Size and wall | NPS 2, Sch. 40S, 6 m random or fixed length |
| Delivery condition | Solution annealed, pickled |
| Testing | Hydrostatic test per specification; eddy current supplementary |
| Certification | EN 10204 Type 3.1, English |
| Quantity | State the quantity and whether spares are included |
| Marking | Specification, grade, heat number, manufacturer marking |
| Delivery term and destination | Trade term and named port or place |
| Applicable code | State the piping code and the ASME Code edition |
The last line is worth adding if it is not already on the order. Because the ASME Boiler and Pressure Vessel Code is published on a two-year cycle and addenda are no longer issued separately, the edition in force can change underneath a long-running project. Stating the edition you are building to removes that ambiguity at no cost.
Send us a specification written this way and we will quote it back against each field, so you can see exactly what is confirmed and what is assumed. Message us on WhatsApp or through our contact page, or browse our nickel alloy seamless pipe and pipe and tube ranges to see what we hold.
