ASTM A312/A312M is a pipe specification for seamless, straight-seam welded and heavily cold-worked austenitic stainless steel. It is commonly used for process piping ordered by nominal pipe size (NPS) and schedule. This guide explains when A312 is appropriate, how seamless and welded routes differ, and when a tube specification such as ASTM A213 or A249 is the better choice.
ASTM A312 pipe: scope and manufacturing routes
A312 covers both major manufacturing routes under one specification. A purchase order still needs to identify the route because seamless (SML), welded (WLD) and heavily cold-worked welded (HCW) pipe are not interchangeable labels.
- Seamless A312 pipe is produced without a longitudinal weld. Review TeCarve’s stainless steel seamless pipe and tube range.
- Welded A312 pipe is formed and welded along the longitudinal seam, then heat treated and tested as required by the order and applicable edition. Review TeCarve’s welded stainless steel pipe and tube range.
- HCW pipe begins as welded pipe and receives heavy cold work to both wall and weld before final annealing. It should be specified explicitly rather than assumed from the word “welded.”
Pipe versus tube: NPS and schedule are not actual dimensions
An A312 pipe order is normally built around NPS plus schedule, for example NPS 2 Schedule 40S. NPS is a nominal designator: it is not a direct measurement of the outside diameter. The schedule identifies a standardized nominal wall thickness for that NPS. A312 also permits other specified outside-diameter and wall combinations, but those dimensions must be stated clearly in the order.
A213 and A249 are tube specifications. Their orders identify the tube by actual outside diameter and wall thickness rather than an NPS/schedule pair. That distinction matters in heat-transfer equipment, where tube-to-tubesheet fit, wall thickness, surface area and thermal resistance are part of the equipment design.
| Specification | Product and process | Usual dimensional language | Primary service context |
|---|---|---|---|
| ASTM A312/A312M | Seamless, welded and HCW austenitic stainless steel pipe | NPS + schedule; specified OD/wall combinations may also be ordered | General corrosive and process-piping service, including low- and high-temperature duties within the governing design code |
| ASTM A213/A213M | Seamless ferritic and austenitic alloy-steel tube | Actual OD + minimum wall, or average wall when specified | Boilers, superheaters and heat exchangers |
| ASTM A249/A249M | Welded and HCW welded austenitic steel tube | Actual OD + nominal wall thickness | Boilers, superheaters, heat exchangers and condensers |
Minimum mechanical properties for common A312 grades
The following values are room-temperature minimum tensile requirements for ASTM A312 pipe. Strength is shown in N/mm², numerically equal to MPa. Elongation is the minimum for a longitudinal specimen measured over 2 in. or 50 mm (or 4D). The corresponding general transverse minimum for these grades is 25%.
| Grade | UNS | Manufacturing / thickness condition | Tensile strength min. | Yield strength min. | Longitudinal elongation min. |
|---|---|---|---|---|---|
| TP304 | S30400 | All covered routes | 515 N/mm² | 205 N/mm² | 35% |
| TP304L | S30403 | All covered routes | 485 N/mm² | 170 N/mm² | 35% |
| TP316 | S31600 | All covered routes | 515 N/mm² | 205 N/mm² | 35% |
| TP316L | S31603 | All covered routes | 485 N/mm² | 170 N/mm² | 35% |
| TP321 | S32100 | Welded; or seamless with nominal wall ≤3/8 in. (9.5 mm) | 515 N/mm² | 205 N/mm² | 35% |
| TP321 | S32100 | Seamless with nominal wall >3/8 in. (9.5 mm) | 485 N/mm² | 170 N/mm² | 35% |
These are specification minima, not typical mill-test results and not design allowable stresses. Confirm the edition named on the purchase order, the specimen orientation, dimensions, heat treatment, supplementary requirements and governing piping code before acceptance.
Chemical composition of common A312 grades
Values are % by mass, maximum unless a range is shown, from Table 1 of ASTM A312/A312M-25 (current edition, approved May 2025). All grades below: Mn 2.00, P 0.045, S 0.030, Si 1.00 max. Confirm limits against the edition named on your order.
| Grade | UNS | C | Cr | Ni | Mo | Other |
|---|---|---|---|---|---|---|
| TP304 | S30400 | 0.08 | 18.0–20.0 | 8.0–11.0 | – | – |
| TP304L | S30403 | 0.035* | 18.0–20.0 | 8.0–13.0 | – | – |
| TP304H | S30409 | 0.04–0.10 | 18.0–20.0 | 8.0–11.0 | – | – |
| TP316 | S31600 | 0.08 | 16.0–18.0 | 10.0–14.0 | 2.00–3.00 | – |
| TP316L | S31603 | 0.035* | 16.0–18.0 | 10.0–14.0 | 2.00–3.00 | – |
| TP316H | S31609 | 0.04–0.10 | 16.0–18.0 | 10.0–14.0 | 2.00–3.00 | – |
| TP321 | S32100 | 0.08 | 17.0–19.0 | 9.0–12.0 | – | Ti 5×(C+N) min, 0.70 max; N 0.10 |
| TP347 | S34700 | 0.08 | 17.0–19.0 | 9.0–13.0 | – | Nb 10×C min, 1.00 max |
| TP310S | S31008 | 0.08 | 24.0–26.0 | 19.0–22.0 | 0.75 | – |
*For small-diameter or thin-wall tubes needing many drawing passes, a carbon maximum of 0.040% is necessary in TP304L and TP316L (small OD: under 0.500 in [12.7 mm]; light wall: under 0.049 in [1.20 mm] average wall). H grades (TP304H, TP316H, TP321H, TP347H…) are versions for service where creep and stress-rupture properties are important, with controlled carbon and grain size.
Heat treatment
All A312 pipe is furnished heat treated. Grades not individually listed in Table 2 — including TP304, TP304L, TP316, TP316L, TP321 and TP347 — are solution annealed at a minimum of 1900 °F [1040 °C] and quenched in water or rapidly cooled. Cold-finished TP321H, TP347H and TP348H require at least 2000 °F [1100 °C]. An intergranular corrosion test to ASTM A262 Practice E is run only when Supplementary Requirement S7 is specified.
Wall thickness tolerance (Table 3)
| NPS | Over | Under |
|---|---|---|
| ⅛ to 2½ incl., all t/D | +20.0% | −12.5% |
| 3 to 18 incl., t/D up to 5% incl. | +22.5% | −12.5% |
| 3 to 18 incl., t/D over 5% | +15.0% | −12.5% |
| 20 and larger, welded, all t/D | +17.5% | −12.5% |
| 20 and larger, seamless, t/D up to 5% incl. | +22.5% | −12.5% |
| 20 and larger, seamless, t/D over 5% | +15.0% | −12.5% |
Source: ASTM A312/A312M-25, Table 3. t = nominal wall thickness, D = ordered outside diameter. Nominal dimensions follow ASME B36.19 — see our stainless steel pipe size and schedule chart.
Tests, lengths and repairs
- Hydrostatic or nondestructive electric test on every pipe, at the manufacturer’s option unless the order specifies one (to ASTM A999/A999M). For NPS 10 and larger the purchaser may, with the manufacturer’s agreement, waive the hydrostatic test in favour of a system test; such pipe is marked “NH”.
- Tension test: one per lot of up to 100 pipes; two for lots over 100 pipes.
- Flattening test on a sample of each lot (at least two lengths); welded pipe may be given a transverse guided face bend test of the weld instead.
- Lengths: unless agreed otherwise, NPS ⅛ to 8 is supplied in lengths up to 24 ft, within 15–24 ft. Cut lengths may not be under the ordered length or more than ¼ in [6 mm] over it. No jointers unless specified.
- Weld repair: only for welded pipe NPS 6 and larger with nominal wall 0.200 in or more, by gas tungsten-arc welding, limited to 20% of the seam length; repaired pipe is identified on the test certificate.
- Certification must state whether the pipe was hydrostatically tested or, if nondestructively tested, which practice and reference discontinuities were used.
Sourcing ASTM A312 Stainless Steel Pipe (Seamless or Welded)?
Supplied in 304L, 316L, and duplex 2205 with hydrostatic or nondestructive electric testing on every pipe and an EN 10204 3.1 MTC as standard.
A312 versus A213 and A249
One pipe standard versus two tube standards
A312 includes seamless and welded pipe in one standard. Heat-transfer tubing separates the routes: A213 is seamless, while A249 is welded or heavily cold-worked welded. Calling out “A213 welded tube” or “A249 seamless tube” creates a specification contradiction.
Process piping versus heat-transfer equipment
A312 is primarily selected for piping systems that carry process fluids between equipment. A213 and A249 are written for tubes installed inside boilers, superheaters, heat exchangers and condensers. Tube orders often impose tighter control of actual OD and wall because tubesheet fit and wall thickness directly affect fabrication and heat-transfer performance; the exact tolerances must still be stated or verified against the applicable standard and drawing.
Do not translate NPS/schedule directly into a tube drawing
A schedule designation selects a nominal pipe wall for a particular NPS. A heat-exchanger drawing normally controls actual OD and wall thickness. Even when two items appear close in size, their permitted variation, testing, finish and documentation can differ. The correct standard follows the equipment function and drawing—not simply the nearest available diameter.
Where A269 and A270 fit
ASTM A269/A269M covers seamless and welded austenitic stainless tubing for general corrosion-resisting and low- or high-temperature service; it is a general-service tube specification, not a dedicated boiler or heat-transfer specification. ASTM A270/A270M is for sanitary tubing used in dairy, food and related hygienic service, with surface-finish requirements central to the order.
A practical A312 purchase-order checklist
- ASTM A312/A312M designation and required edition
- Grade and UNS designation, such as TP304L / S30403 or TP316L / S31603
- Manufacturing route: seamless, welded or HCW
- NPS and schedule, or explicitly specified OD and wall thickness
- Quantity, cut length and end preparation
- Required hydrostatic or nondestructive electric test and any supplementary tests
- Heat treatment, surface condition, marking and certification requirements
- Applicable design code and service conditions, which are separate from the material specification
Next Steps: ASTM A312 Pipe Procurement & Sourcing
Reply within 24 hours. Standard pipe orders start from 100–300 kg. In-stock standard sizes ship in 7–10 days; custom production orders ship in 10–25 days.
Seamless (Wenzhou) and welded (Foshan) piping consolidated into a single shipment from the two dedicated plants.
Multi-channel eddy current and hydrostatic testing, plus PMI verification on every batch before shipment.
Flexible international shipping terms with seaworthy wooden cases or pallets directly to your facility.
A: Every pipe undergoes full non-destructive testing via multi-channel eddy current, with hydrostatic testing per the ordered standard or purchase order. PMI verification is performed on every batch before shipment (piece-by-piece on request), and full chemistry and mechanical data are documented on the EN 10204 3.1 MTC.
A: Yes. TeCarve is a specialized Chinese stainless steel piping solutions provider and the exclusive factory-direct export channel for two dedicated manufacturing plants in Foshan (welded & decorative tubing) and Wenzhou (seamless & precision tubing). TeCarve consolidates seamless and welded piping into a single commercial invoice, packing list, and shipment, eliminating multiple vendor handoffs.
Related TeCarve technical references
If the open question is material grade rather than product standard, use the 304, 316 and 316L stainless steel grade and product-form hub. After the grade and specification are defined, review either the seamless pipe range or welded pipe range for the relevant manufacturing route.
Related standards and grade guides: ASTM A999 general requirements and tolerances · ASTM A358 EFW pipe · ASTM A790 duplex pipe · 310S stainless steel pipe · 321 stainless steel tube & pipe · ASME B31.3 pressure rating chart.