ASTM A213 TP321H Stainless Steel Bright Annealed Tube for Heat Exchanger

What Is ASTM A213 TP321H?

ASTM A213 TP321H is a titanium-stabilized austenitic stainless steel tube grade covered by ASTM A213, the specification for seamless ferritic and austenitic alloy-steel boiler, superheater and heat-exchanger tubes. The H suffix identifies a controlled carbon range of 0.04 to 0.10 percent, which raises creep strength at elevated temperature compared with standard TP321. The grade is registered as UNS S32109 and corresponds to JIS SUS321H and, in plate and strip forms, to EN X6CrNiTi18-10 (1.4940).

Titanium is the key alloying addition. It combines preferentially with carbon to form stable titanium carbides, so chromium carbides do not precipitate at grain boundaries during welding or high-temperature service. As a result, TP321H resists intergranular corrosion even after welding, and it can be used in the sensitization range of roughly 425 to 850 C without the loss of corrosion resistance seen in unstabilized grades.

Chemical Composition (ASTM A213)

Element	Requirement (wt %)
Carbon (C)	0.04 - 0.10
Manganese (Mn)	2.00 max
Phosphorus (P)	0.045 max
Sulfur (S)	0.030 max
Silicon (Si)	0.75 max
Chromium (Cr)	17.00 - 19.00
Nickel (Ni)	9.00 - 12.00
Titanium (Ti)	4 x C min, 0.60 max
Iron (Fe)	Balance

Mechanical Properties (Annealed)

Property	Value
Tensile strength	515 MPa min
Yield strength (0.2% offset)	205 MPa min
Elongation in 2 in	35% min
Density	about 8.0 g/cm3

Values apply to the annealed condition as required by ASTM A213 for seamless tube.

Why Bright Annealing Matters

Bright annealing is performed in a protective atmosphere of hydrogen or nitrogen instead of air, so the tube surface remains free of oxide scale after heat treatment. For heat exchanger tubing, the bright, clean surface reduces fouling, improves heat transfer and simplifies subsequent cleaning and passivation. The finish is especially valued in sanitary and high-purity process lines where surface quality directly affects service life.

Service Temperature and Applications

TP321H is commonly rated for continuous service up to approximately 870 C, and the H carbon range provides higher allowable design stresses than TP321 above about 540 C. Typical applications include boiler superheater and reheater tubes, feedwater heaters, refinery heater tubes, petrochemical heat exchanger tubing and welded pressure-vessel internals that operate between 425 and 850 C after welding.

Welding and Fabrication

The grade welds readily by conventional methods including TIG and MIG. Matching filler such as ER321 is recommended so that the weld metal retains titanium stabilization; ER347 is an alternative where columbium stabilization is preferred. The tube can be cold bent and flared using standard austenitic practice. Because of the titanium addition, the weld pool must be protected by adequate shielding gas to avoid titanium oxidation.

FAQ

1. What does the H suffix mean in TP321H?

The H indicates a controlled carbon content of 0.04 to 0.10 percent, which improves creep strength and high-temperature design allowables relative to standard TP321.

2. How does TP321H differ from TP321?

Both are titanium stabilized. TP321H carries the higher controlled carbon range and is specified where long-term creep resistance at elevated temperature is required, for example in boiler tubing. TP321 is chosen where maximum corrosion resistance after welding is the priority.

3. Is TP321H resistant to intergranular corrosion after welding?

No stainless steel is immune, but titanium stabilization suppresses chromium carbide precipitation, so TP321H shows good resistance to intergranular corrosion in the as-welded condition within its design temperature range.

4. What filler metal is used to weld TP321H?

ER321 filler is the common choice because it maintains titanium stabilization in the weld metal. ER347 is a widely used alternative where niobium stabilization is preferred.

5. What is the maximum service temperature for TP321H tubes?

Continuous service is commonly rated to about 870 C. Above this range, creep and oxidation behavior should be reviewed against the governing design code for the specific component.

6. Can TP321H be used in chloride environments?

TP321H is an austenitic grade without molybdenum, so its resistance to chloride pitting is limited. For seawater or high-chloride process duty, a molybdenum-bearing grade such as 316L or 316Ti is the better choice.