What is the difference between A335 A335M steel tube and A213 alloy tubes?

If you are specifying a ferritic alloy component for a boiler, superheater, heat exchanger, or high-pressure steam line, you have likely run into a recurring question: should I order an ASTM A335/A335M alloy steel pipe or an ASTM A213/A213M alloy tube? Both standards are written by the same committee, both serve high-temperature service, and both look similar on a mill test report. But they are not interchangeable, and choosing the wrong one can derail procurement, fabrication, or final inspection.

This guide walks through the practical differences between the two specifications, the grades you will meet most often, and how to decide which one belongs in your project. As a manufacturer and integrated supplier of carbon and alloy steel industrial piping, we see this question every week from EPC contractors, power plant engineers, and pressure vessel fabricators.

Quick answer: pipe vs. tube

The cleanest way to remember the difference is that A335 covers pipe and A213 covers tube. In ASME B36 terminology, a pipe is a pressure-bearing component sized by nominal diameter and schedule, while a tube is sized by exact outside diameter and wall thickness and is typically used in heat-transfer or instrumentation service. ASTM A335/A335M specifies seamless ferritic alloy-steel pipe for high-temperature service, while ASTM A213/A213M specifies seamless ferritic and austenitic alloy-steel tubes for boilers, superheaters, and heat exchangers.

If you are routing steam between two headers, you are buying A335. If you are putting a serpentine coil inside a firebox, you are buying A213.

Scope and material coverage

ASTM A335/A335M covers seamless ferritic alloy-steel pipe. The grade naming convention uses the letter P (for pipe): P1, P2, P5, P5c, P9, P11, P12, P15, P21, P22, P23, P24, P36, P91, P92, P122, and the related Type I and Type II designations. These grades are designed for elevated-temperature creep resistance in power and process piping.

ASTM A213/A213M covers seamless ferritic and austenitic alloy-steel tubes, plus austenitic stainless steel tubes, used in boilers, superheaters, and heat exchangers. Grades use the letter T (for tube): T2, T5, T5b, T5c, T9, T11, T12, T17, T21, T22, T23, T24, T36, T91, T92, T122, and on the stainless side TP304, TP304H, TP304L, TP316, TP316H, TP316L, TP321, TP321H, TP347, TP347H, and so on. A335 is alloy-only; A213 is alloy and stainless.

That single distinction decides a lot of projects. The ASTM A312/A312M austenitic stainless line covers general corrosive service pipe, while A213 TP304H and TP316H is the tube you specify for superheater panels in a utility boiler.

Dimensions, tolerances, and delivery condition

A335 pipe is produced to ASME B36.10M (carbon and alloy) and ASME B36.19M (stainless) dimensional tables in sizes typically from 1/2 in. NPS up to 26 in. or larger for project work. Wall thickness is selected from schedule 40 through XXS, with a permitted minimum wall calculation. A213 tube is produced to exact OD and wall, generally from about 1/8 in. OD up to 5 in. OD for boilers and exchangers, with tighter OD and wall tolerances suitable for rolling, bending, and finning.

Delivery conditions also differ. A335 pipe is most commonly ordered in the normalized and tempered, quenched and tempered, or annealed condition depending on grade. A213 tube is typically ordered in the cold-drawn or hot-finished condition, often with a final solution anneal for stainless grades such as TP304H and TP316H. Our heat efficiency tube range, including U-bend and finned tubes, draws on this same A213 stock and applies additional cold bending and post-bend heat treatment for exchanger fabrication.

Mechanical properties: a side-by-side example

The chemistry of P91 and T91 grade is essentially the same 9 percent Cr, 1 percent Mo, V, Nb alloy. The mechanical targets are also aligned:

Tensile strength (min): 585 MPa (85 ksi)
Yield strength (min): 415 MPa (60 ksi)
Hardness (max): 250 HBW or 25 HRC
Elongation in 2 in. (min): about 20 percent

What changes is the test orientation, sample location, and the dimensional acceptance window. A335 P91 requires hydrostatic testing on every length, while A213 T91 requires a flattening test, flare test, or flange test on each tube, plus the same NDT regime. For high-temperature headers and main steam piping in a 600 degrees Celsius class unit, our ASTM A335/A335M P91 pipe is supplied with full MTC, EN 10204 3.1 or 3.2 on request, and 100 percent ultrasonic or eddy-current testing in line with ASME V Article 23.

Where each standard is used

Typical A335/A335M applications

Main steam, hot reheat, and cold reheat piping in utility and industrial power plants.
High-pressure feedwater lines, supercritical and ultra-supercritical loops.
Refinery and petrochemical cracker piping, including transfer lines operating above 400 degrees Celsius.
Boiler external piping between the steam drum and superheater outlets.
High-pressure hydrocarbon and synthesis gas service in fertilizer, methanol, and hydrogen plants.

Typical A213/A213M applications

Boiler tubes for waterwalls, screen tubes, and roof tubes.
Superheater and reheater panels, including TP304H, TP316H, T91, and T92.
Heat exchanger and condenser tubing, also covered by our ASTM A179/A179M seamless low-carbon tube range for the lower-temperature end.
Fired heater coils in ethylene and reformer plants.
Cold-end stainless tubing in district heating and seawater-cooled condensers.

Are A335 and A213 interchangeable?

No, and the reasons go beyond paperwork. Three practical constraints decide it:

Geometry. Pipe schedule and tube OD/wall tables do not match. Swapping one for the other usually forces a redesign of the support, nozzle, or bend layout.
Testing regime. A335 requires hydrostatic pressure testing of every pipe; A213 requires flattening or flare testing of every tube. Each is a different acceptance test, and the project QA plan has to align.
Material coverage. A335 is ferritic alloy only. If you need a stainless heat-exchanger tube, there is no A335 grade that will satisfy the spec.

If a design needs pipe dimensions and pressure ratings, the correct call is A335. If the design needs tight-tolerance tubing that will be bent, finned, or rolled into a tube sheet, the correct call is A213. The same chemistry can be supplied under either spec, and the material is the same in the furnace, but the documentation, dimensional checks, and the way it is allowed to be installed in your system are not.

Procurement checklist for A335 vs. A213

Before you issue a purchase order, lock down the following so the mill does not have to guess:

Standard and edition: ASTM A335/A335M-22 or A213/A213M-22 are typical. Older editions may still be referenced in legacy project specs.
Grade and UNS number: for example A335 P91 (UNS K91560) or A213 T22 (UNS K21590).
Size: NPS and schedule for pipe; OD x minimum wall, exact or average, for tube.
Length: random, single random, or cut to length, plus any U-bend leg length if applicable.
Heat treatment condition: normalized and tempered, quenched and tempered, or solution annealed.
NDT scope: 100 percent UT or ET, plus radiographic spot testing if specified by the project.
Documentation: MTC to EN 10204 3.1, 3.2 where required, PMI report, and NDT reports.
Applicable code: ASME B31.1, B31.3, or B31.7 for the system the material is going into.

A clear specification at the inquiry stage saves weeks of clarification emails and reduces the risk of a wrong-grade rejection at site.

Where EZ Steel Industrial fits

We produce both A335/A335M and A213/A213M material across our three-site network: Cangzhou for alloy steel pipe inventory and custom fittings, Yangzhou for large-scale carbon and alloy pipe production, and Lishui for stainless and copper-nickel corrosion-resistant materials. Our scope extends beyond pipe and tube into matching butt-weld fittings, steel flanges, gaskets, stud bolts, and industrial valves, so a project can be supplied as a single coordinated package rather than as a list of unrelated items.

Quality control covers ISO 9001 management, API 5L and API 5CT product certification, and PED compliance where required. Hydrostatic, ultrasonic, eddy-current, PMI, and visual inspections are carried out at more than 12 checkpoints along the production route, with mill test certificates issued per EN 10204 3.1 as standard and 3.2 available on request. If you are weighing a big diameter steel pipe for a main steam line against a boiler tubing bundle for a new heat exchanger, our engineering team can review your datasheet and recommend the most cost-effective grade, dimensional, and test combination before you commit.

Send your inquiry to export@ezsteelpipe.com with line items, grades, sizes, and any project-specific clauses, and we will return a quotation and technical response within one working day.