ASTM A312 vs A269 vs A213: Pipe & Tube Standards Compared

The mill certificate can be perfect and the material still wrong for the job. That is what happens when tubing bought to ASTM A269 ends up in a duty that needed ASTM A213, because both arrived stamped 316L and both looked identical stacked on the rack. These three standards are not grades, and they are not quality levels. ASTM A312, A269 and A213 are three different answers to one question, which is what the material has to survive, and choosing between them decides the product form, the dimensioning and the mandatory testing on your stainless steel pipe and tube order. The table below is the short version. Get it right at enquiry stage and the rest of the order looks after itself.

These are typical published scopes. Confirm against the current edition of each standard before it governs a purchase order.

If you take nothing else: pressure piping points to A312, heat transfer points to A213, instruments and general service point to A269.

ASTM A312: the process piping specification

A312 is the one most buyers of stainless pipe are actually working to, often without naming it. 

It covers seamless, welded and heavily cold-worked austenitic stainless steel pipe, in the familiar 300-series grades plus the higher alloys. It is dimensioned the way pipe is dimensioned, by nominal pipe size and schedule, which is why SCH 40 and SCH 80 belong to this conversation and not to the other two.

What it is written for: fluid under pressure, in a corrosive environment, at temperature. Heavier walls, larger bores, and a mandatory pressure or non-destructive test regime.

Grades commonly supplied to A312 include TP304 and TP304L, TP316 and TP316L, TP317L, TP321, TP347 and TP310S. In practice that means SS 304 pipe for general corrosion service, SS 317L where molybdenum content needs raising, and SS 904L where the chemistry gets genuinely aggressive.

A312 permits welded pipe. That surprises people who assume a pressure specification implies seamless. It does not, and the welded product is subject to the examination the standard requires. What changes downstream is the design allowance, which is covered in seamless vs welded steel pipe.

ASTM A269: the general service tubing specification

A269 covers seamless and welded austenitic stainless steel tubing for general corrosion-resisting service. It is dimensioned by outside diameter and wall thickness, with tight dimensional tolerances, because it has to fit compression fittings and instrument ferrules that do not forgive variation.

Where it belongs: instrument air and impulse lines, sampling systems, hydraulic and pneumatic lines, panel tubing, light process work, food and pharmaceutical transfer where surface finish matters more than pressure capability.

Where it does not belong: a pressure header, a steam line, or anything with a fired duty.

The critical difference is what the standard obliges the mill to do. Under A269, hydrostatic testing is not mandatory by default. It can be a purchaser requirement, and non-destructive examination can substitute for it. That flexibility is exactly right for a sampling line and exactly wrong for a header. The tube is not badly made. It was simply never specified to prove anything about pressure containment, and no amount of correct paperwork changes that.

The point that matters commercially: A312 and A213 have ASME equivalents, SA-312 and SA-213, which is what allows the material to be used under the boiler and pressure vessel code and to appear in design allowable stress tables. A269 does not have that equivalence. This is the real reason A269 tubing cannot simply be substituted into a pressure application, and it is not something a mill test certificate will tell you.

ASTM A213: the fired and heat transfer specification

A213 covers seamless ferritic and austenitic alloy-steel tubes for boilers, superheaters and heat exchangers. Two things separate it from the other two.

It is a seamless specification. No welded product. If a project requires welded tube to an equivalent duty, the specification to reach for is A249, not A213 with an exception written into the purchase order.

Its material range is wider than stainless. A213 includes the low-alloy chromium-molybdenum grades, T11, T22 and T91 among them, alongside austenitic grades such as TP304H, TP316H, TP321H, TP347H and TP310S. The H grades are there for a reason: controlled carbon and grain size, because the governing property at temperature is creep resistance, not room-temperature yield.

The test regime is the heaviest of the three. Flattening, flaring, hardness, hydrostatic or eddy current examination, and grain size requirements on the grades where it matters. That regime is the whole point. These tubes sit in fired environments where a failure is not a leak, it is an incident.

Pipe or tube: the dimensional difference that causes the confusion

A large share of the A312 versus A269 confusion is not about pressure at all. It is about how the product is measured.

• Pipe is called out by nominal pipe size and schedule. NPS 2 SCH 40. The nominal number is a designator, not a measurement, and the outside diameter is fixed regardless of wall. The steel pipe size chart sets this out in full.
• Tube is called out by actual outside diameter and actual wall thickness. 25.4 mm OD by 2.11 mm wall. The number on the order is the number you can measure.

So an enquiry that says “2 inch, 316L, schedule 10” is asking for pipe, whatever the word used, and an enquiry that says “25.4 mm OD by 1.65 mm wall” is asking for tube. When the two conventions get mixed inside one requisition, the wrong specification follows almost automatically.

Dual certification, and why the certificate is not the whole answer

Material is often dual certified, most commonly to both the ASTM specification and its ASME counterpart, and frequently across grades as well, such as TP316/316L where the chemistry satisfies both.

Dual certification is genuinely useful. It is also frequently over-read. Certification to two standards means the material meets the requirements of both as tested. It does not mean the two standards are interchangeable, and it does not upgrade material from a general service specification into a pressure service one.

Read the certificate for what it says: this heat, these tests, these results, against these specifications. Then check that the specification named is the one your design basis calls for. Those are two separate checks and only the second one is about your application.

Beyond the three

These are austenitic and alloy steel specifications. Once the service moves outside that range, so does the standard:

• Duplex and super duplex pipe run to their own specifications, not A312. Our duplex 2205 pipe range covers that ground.
• Nickel alloy pipe and tube, Inconel, Monel, Hastelloy and Alloy 20, carry ASTM B-series specifications rather than A-series.

If a specification named on your enquiry does not match the material you are asking for, tell us and we will confirm what applies before anything is quoted.

What to send us

Four lines remove nearly all ambiguity:

1. The specification and grade, for example ASTM A312 TP316L, not just “316L”
2. Pipe or tube, and dimension it the matching way: NPS and schedule for pipe, OD and wall for tube
3. The service, briefly. Pressure, temperature, medium. This is what lets us flag a specification mismatch before it becomes an order.
4. Length, quantity and end finish

Send us the OD, wall, schedule and length and we will confirm availability and the applicable standard.