ASTM A213 Seamless Stainless Steel Tube Standard

What is ASTM A213?

ASTM A213 is the Standard Specification for Seamless Ferritic and Austenitic Alloy-Steel Boiler, Superheater, and Heat-Exchanger Tubes. It was first published by ASTM International and is maintained under the jurisdiction of ASTM Committee A01 on Steel, Stainless Steel, and Related Alloys.

The specification covers tubes intended for use in boilers, superheaters, heat exchangers, and condensers. Tubes are produced by the seamless process either hot finished or cold finished, and are supplied in the heat-treated condition.

ASTM A213 tubing critically differs from ASTM A312 pipes: A213 covers tubes (specified by OD and wall thickness), while A312 covers pipes (specified by NPS and schedule). Tubes under A213 are designed specifically for pressure-containing heat-transfer applications such as boilers and heat exchangers, while A312 pipes are specified for high-temperature and general corrosive fluid conveyance under pressure.

Heat Treatment Requirements for ASTM A213

Heat treatment is mandatory for all ASTM A213 tubes. The method varies between austenitic and ferritic grade families. Proper heat treatment controls grain size, relieves residual stress, and sets the final mechanical properties.

Austenitic grades (TP304, TP316, TP321, TP347, etc.): All austenitic tubes must be solution annealed at a minimum temperature of 1900°F (1040°C) and then quenched in water or rapidly cooled by other means. This dissolves chromium carbides back into the matrix and restores full corrosion resistance.

H grades (TP304H, TP321H, TP347H): the grain size after solution annealing must be ASTM No. 7 or coarser. This coarser grain structure improves creep resistance at service temperatures above 1000°F (538°C).

Ferritic grades (T11, T22, T91, T92, etc.): Ferritic alloy-steel tubes must be normalised and tempered, or full-annealed, or isothermal-annealed. For T91, the normalising temperature is 1900°F (1040°C) minimum, followed by tempering at 1350°F (730°C) minimum.

Testing and Inspection Requirements

ASTM A213 mandates several tests to verify tube quality before shipment. Every lot must pass chemical analysis, mechanical testing (tension and hardness), and either a hydrostatic test or a nondestructive electric test (NDE). Here is a summary of each required test.

Tension Test

One tension test should be performed per batch for batches of 50 tubes or fewer. For batches over 50, 2 specimens are required. The test measures tensile strength, yield strength (0.2% offset), and elongation in 2 in. (50 mm) or 4D gauge length.

Flattening Test

One flattening test should be performed on specimens from each end of one finished tube per batch. The tube section is flattened between parallel plates until the distance between plates reaches a value determined by the tube’s OD-to-wall ratio. No cracks or splits should appear.

Flaring Test

One flaring test should be conducted from each end of one finished tube per batch. The tube end is expanded over a 60° tapered mandrel until the OD increases by a specified percentage. The tube must show no cracks or breaks.

Hardness Test

Brinell or Rockwell hardness tests should be performed on 2 tubes per batch. Most austenitic grades must not exceed 192 HB / 200 HV / 90 HRB. Ferritic grade limits vary (for example, T91 must not exceed 250 HB / 265 HV / 25 HRC).

Hydrostatic or NDE Test

Every tube must pass either a hydrostatic pressure test or a nondestructive electric test (eddy current per ASTM E426). The hydrostatic test pressure is calculated using the formula: P = 2St/D, where S = allowable stress (60% of specified minimum yield), t = wall thickness, and D = outside diameter.