ASTM A312 and ASTM A213 are both seamless (or welded, for A312) stainless steel specifications, and both can use the same 304/316-series grades — but they are not interchangeable. A312 is a pipe specification for general corrosive/process service; A213 is a tube specification built specifically for boiler, superheater, and heat-exchanger duty. Mixing them up on an order is a common and costly mistake.
Core Difference: Pipe vs Tube Service
- ASTM A312 (Pipe): Covers seamless and welded austenitic stainless steel pipe for general corrosive and high-temperature process service — chemical plants, process piping, structural and transport lines. Sized by NPS (nominal pipe size) per ASME B36.19M, with a looser wall-thickness tolerance (typically +20% / −12.5%).
- ASTM A213 (Tube): Covers seamless ferritic and austenitic alloy-steel tubes specifically for boiler, superheater, and heat-exchanger service — where heat transfer efficiency and dimensional precision matter more than general flow capacity. Sized by actual OD and wall thickness (NPS shown only as a reference), with a tighter, zero-under tolerance (typically +20–22% / −0%) since wall thickness directly affects heat-transfer calculations and burst margins in a boiler.
Side-by-Side Comparison
| Aspect | ASTM A312 (Pipe) | ASTM A213 (Tube) |
|---|---|---|
| Primary Use | General corrosive/process service piping | Boiler, superheater & heat-exchanger tubing |
| Sizing Basis | NPS (nominal pipe size) | Actual OD + wall thickness (NPS for reference only) |
| Wall Thickness Tolerance | Looser (allows under-tolerance, e.g. −12.5%) | Tighter, essentially zero under-tolerance |
| Mandatory NDT | Hydrostatic or UT (per order) | Eddy current test (ASTM E426) typically mandatory, plus hydrostatic |
| Common Grades | TP304/304L, TP316/316L, TP321, TP347 | TP304/304L, TP316/316L, TP321 (austenitic); plus ferritic grades like T5, T9, T22 |
| Governing Code | ASME B31.3 (process piping) | ASME Section I (boiler & pressure vessel code) |
Why This Matters When Ordering
Specifying A312 pipe where the application actually calls for A213 tube (or vice versa) can mean the material fails inspection or doesn’t meet the project’s code requirements — even if the grade (e.g. 316L) and nominal size look identical on paper. Always confirm with your project’s piping/mechanical engineer which specification the drawing or datasheet calls for before placing the order.
Tolerance and test figures above are typical/representative; always verify exact values against the current edition of ASTM A312 and A213 for code-stamped or critical-service orders. Seamless Steel Industries supplies both A312 pipe and A213 tube in stainless and alloy grades — specify your application and we’ll confirm the correct specification with you.