ASME SA 249 TP304 Welded Stainless Steel Tube: Specification and Properties

Breaking Down the Designation SA 249 TP304

SA 249 TP304 describes a welded austenitic stainless steel tube made to the ASME SA 249 specification from Type 304 material. Each part of the designation carries a specific meaning.

SA identifies a specification issued under the ASME Boiler and Pressure Vessel Code, Section II, Part A. ASME SA 249 is technically identical to ASTM A249; the ASME version is the one referenced when the tube forms part of a code-stamped pressure vessel or fired heater.

249 is the specification number for welded austenitic steel tubes intended for boilers, superheaters, heat exchangers and condensers.

TP stands for tube or pressure grade, distinguishing tube dimensions and tolerance practice from pipe schedules.

304 is the base austenitic grade, the classic 18/8 chromium-nickel stainless steel with roughly 18% chromium and 8% nickel.

The scope of the specification covers welded tube from approximately 3.2 mm to 127 mm outside diameter with wall thickness from about 0.4 mm to 8.1 mm, which is the working range for most shell-and-tube exchanger and condenser tubing.

Chemical Composition of TP304

Element	TP304 (%)	TP304L (%)	TP304H (%)
Carbon (C)	≤ 0.08	≤ 0.035	0.04 - 0.10
Manganese (Mn)	≤ 2.00	≤ 2.00	≤ 2.00
Phosphorus (P)	≤ 0.045	≤ 0.045	≤ 0.045
Sulphur (S)	≤ 0.030	≤ 0.030	≤ 0.030
Silicon (Si)	≤ 1.00	≤ 1.00	≤ 1.00
Chromium (Cr)	18.0 - 20.0	18.0 - 20.0	18.0 - 20.0
Nickel (Ni)	8.0 - 11.0	8.0 - 12.0	8.0 - 11.0
Iron (Fe)	Balance	Balance	Balance

The carbon level is the practical decision point. Type 304 is the general-purpose choice for continuous service up to about 800 degrees Celsius where intergranular corrosion is not a concern; Type 304L is selected for welded assemblies that see aggressive wet service, because the lower carbon prevents chromium carbide precipitation in the weld heat affected zone; Type 304H with its higher carbon and controlled grain size is chosen where creep strength matters at elevated temperature.

Mechanical Properties

Property	TP304	TP304L	Test Standard
Tensile strength, Rm	≥ 515 MPa	≥ 485 MPa	ASTM A370 / ISO 6892-1
0.2% proof strength, Rp0.2	≥ 205 MPa	≥ 170 MPa	ASTM A370 / ISO 6892-1
Elongation in 50 mm	≥ 35%	≥ 35%	ASTM A370 / ISO 6892-1
Hardness	≤ 90 HRB	≤ 90 HRB	ASTM E18

These are minimum values for the delivered, solution-annealed condition. Tube is normally supplied annealed and pickled or bright annealed, with the weld bead either left in place or scarfed flush depending on the ordering option and the exchanger design.

Welded SA 249 Tube Against Seamless SA 213 Tube

Feature	ASME SA 249 TP304	ASME SA 213 TP304
Construction	Welded, formed from strip	Seamless, pierced and cold reduced
Typical service	Boiler, superheater, heat exchanger, condenser	Boiler, superheater, heat exchanger
Pressure capability	Good, governed by weld quality and joint efficiency	Higher, preferred for critical high-pressure duty
Wall uniformity	Excellent, strip thickness is closely controlled	Subject to normal seamless eccentricity
Relative cost	Lower per metre	Higher per metre
Availability	Widely stocked in common exchanger sizes	Longer lead times in special sizes

The two specifications are not interchangeable by default. Design codes apply a weld joint efficiency factor to welded tube, and a retubing project must keep the original specification or obtain engineering approval for a substitution. Where pressure and thermal cycling are severe, seamless tube remains the conservative choice; where the duty is moderate and the quantity is large, welded tube usually wins on both cost and delivery.

Manufacture, Heat Treatment and Testing

Forming and welding: strip is roll formed to a cylindrical section and continuously welded, normally by gas tungsten arc welding with or without filler metal, or by laser welding for thin walls.

Solution annealing: austenitic tube is heat treated at a minimum of 1040 degrees Celsius and rapidly cooled so that carbides stay in solution and the tube is fully soft and corrosion resistant.

Pressure testing: every tube is tested either hydrostatically or by eddy current examination in accordance with the specification; eddy current testing is the usual choice for condenser and exchanger tube because it inspects the full length at high speed.

Mechanical tests: tensile and hardness tests are taken from the lot, with flattening, flange and reverse bend tests applied to the weld to confirm ductility and joint soundness.

Dimensional control: outside diameter, wall thickness and length tolerances follow the general requirements of ASTM A1016 and A1016M, which is also where the limits on straightness and square cut ends are defined.

Documentation: tubes are released with a mill test certificate to EN 10204 3.1 that lists heat number, chemistry, mechanical results and the specification edition applied.

Where SA 249 TP304 Tubes Are Used

Shell-and-tube heat exchangers and feedwater heaters in power and process plants.

Condensers for steam turbines and refrigeration systems.

Superheater and reheater sections of boilers where moderate oxidation resistance is sufficient.

Petrochemical and refinery process units handling clean, non-chloride streams.

Brewery, dairy and food processing lines that require hygienic, corrosion-resistant tubing.

Marine, desalination and instrumentation applications where 316L is not required for chloride resistance.

Frequently Asked Questions

Q: Is ASME SA 249 the same as ASTM A249?
Yes. The technical requirements are identical, including chemistry, mechanical properties and testing. The ASME edition is used when the tube is supplied against the Boiler and Pressure Vessel Code, for example for a code-stamped exchanger.

Q: What does the TP in TP304 mean?
TP indicates a tube or pressure grade rather than a pipe schedule. It signals that the material is ordered as tube with tube dimensions and tolerances, which are tighter than those applied to standard pipe.

Q: Should I order TP304 or TP304L?
Choose TP304L when the tube is welded into a structure and will see wet, potentially corrosive service, because the low carbon prevents sensitisation in the weld zone. Choose TP304 where higher annealed strength is useful and intergranular corrosion is not a risk. Choose TP304H for elevated temperature creep duty.

Q: Can SA 249 tube handle high pressure?
It can handle substantial pressure, but the welded seam means design codes apply a joint efficiency below unity. For very high pressure or severe thermal cycling, seamless SA 213 TP304 is normally specified instead.

Q: What heat treatment is required?
All austenitic tube under this specification is solution annealed at a minimum of 1040 degrees Celsius followed by rapid cooling. This restores the passive film, softens the weld zone and dissolves carbides that would otherwise reduce corrosion resistance.

Q: Which tests are performed on each tube?
Every tube receives a hydrostatic or eddy current test. Lot testing adds tensile, hardness, flattening, flange and reverse bend tests, with intergranular corrosion testing added only when it is specified on the purchase order.