ASTM A249 TP321 Welded Stainless Steel Heat Exchanger Tube Explained

What Is ASTM A249 TP321 Welded Tube?

ASTM A249 welded boiler tube covers nominal-wall-thickness welded tubes and heavily cold worked welded tubes made from austenitic steel to the A249 specification, for service in boilers, superheaters, heat exchangers and condensers. TP321 is the titanium-stabilised grade: chromium runs from 17.0% to 19.0%, nickel from 9.0% to 12.0%, and titanium is added at a minimum of five times the carbon plus nitrogen content, with a maximum of 0.70%.

Stabilising the grade with titanium keeps carbon from combining with chromium at the grain boundaries, so the tube resists sensitisation and intergranular corrosion through welding and through long exposure at elevated temperature. That behaviour, together with good formability and weldability, is why TP321 welded tube is widely specified for heat exchanger and boiler tube bundles.

Surface Condition and Dimensional Limits

After final heat treatment, tube that has been annealed in air is chemically descaled or pickled to remove oxide scale. If the bright annealing process is used instead, pickling or chemical descaling is not required, because the controlled furnace atmosphere leaves no scale on the surface.

The dimensions and wall thicknesses normally available for A249 TP321 welded tube run from an inner diameter of 1/8 in (3.2 mm) to an outside diameter of 12 in (304.8 mm), with wall thickness from 0.015 in (0.4 mm) to 0.320 in (8.1 mm). Welded tube is produced in sizes from 1/2 in NB to 16 in NB, in round, square, rectangular and hydraulic forms, in single random, double random and cut lengths, with plain, bevelled or threaded ends.

Specification and Size Table

Item	Value
Specifications	ASTM A249 / ASME SA249
Type	ASTM A249 TP321 stainless steel welded tube
Outside diameter	1/8 in to 12 in (3.2 mm to 304.8 mm)
Welded size	1/2 in NB up to 16 in NB
Wall thickness	0.015 in to 0.320 in (0.4 mm to 8.1 mm)
Length	Single random, double random and cut length
Form	Round, square, rectangular, hydraulic, U-bend
End	Plain end, bevelled end, threaded
Processing	Bending, welding, decoiling, punching, cutting, moulding

Equivalent Grades, Composition and Mechanical Properties

Grade TP321 corresponds to UNS S32100, Werkstoff number 1.4541 and the European designation X6CrNiTi18-10. Composition limits, percent by mass:

Grade	C max	N max	Mn max	P max	S max	Si max	Cr	Ni	Ti
TP321	0.08	0.10	2.00	0.045	0.030	1.00	17.0-19.0	9.0-12.0	5(C+N) min, 0.70 max

Mechanical properties of the finished welded tube:

Tensile strength, min	Yield strength, 0.2% proof, min	Elongation in 50 mm, min	Hardness, max
515 MPa	205 MPa	40%	95 HRB / 217 HB

Tubes are solution annealed and quenched, which dissolves carbides and restores the austenitic structure. Titanium carbides formed during stabilisation remain stable at high temperature, helping the tube hold its strength and oxidation resistance in superheater and heat exchanger duty.

Applications and Value Added Services

ASTM A249 TP321 welded tube is used across the heat exchanger, boiler and condenser sectors, and more widely in:

Gas processing plants and petrochemical units

Power generation boilers, superheaters and reheaters

Food processing and chemical process equipment

Pressure vessels and general corrosion-resistant piping circuits

Cold drawn, cold rolled, hot rolled and extruded tube products

Available services include cutting, bevelling, threading, commercial and electrolytic polishing, drawing and expansion to a required size and length, bending, annealing and pickling, sand blasting and machining. Destructive and nondestructive testing, including ultrasonic examination, is carried out as part of the inspection plan, and heavy wall or large diameter sizes can be produced to order.

Frequently Asked Questions

Q: What does ASTM A249 cover?
It covers welded austenitic stainless steel tubes, both nominal-wall-thickness and heavily cold worked, for boiler, superheater, heat exchanger and condenser service.

Q: What is the composition of TP321?
Chromium 17.0-19.0%, nickel 9.0-12.0%, carbon 0.08% max, manganese 2.00% max, silicon 1.00% max, and titanium at 5(C+N) minimum up to 0.70% maximum.

Q: How is TP321 welded tube finished?
Either annealed and pickled, where oxide scale is removed by chemical descaling or pickling, or bright annealed, which leaves a scale-free surface that needs no pickling.

Q: What sizes are available?
From 1/8 in (3.2 mm) inner diameter to 12 in (304.8 mm) outside diameter, with wall thickness from 0.015 in (0.4 mm) to 0.320 in (8.1 mm).

Q: Which industries use this grade?
Power generation, petrochemical, gas processing, chemical, food processing and other plants that rely on heat exchanger, boiler and condenser tubing.

Q: What testing is carried out?
Both destructive and nondestructive tests are applied, including ultrasonic examination, dimensional checks and mechanical testing on the finished tube.