ASTM A213 TP304 Stainless Steel U-Tube for Heat Exchangers

ASTM A213 TP304 is the specification for seamless austenitic stainless steel tubes for boilers, superheaters and heat exchangers, with TP304 corresponding to UNS S30400. U-tubes are manufactured by cold bending a seamless tube into a U shape with a controlled bend radius, and are the standard tube form for floating-head and fixed-tubesheet shell-and-tube heat exchangers where thermal expansion is accommodated by the bend.

Chemical composition (ASTM A213 TP304, wt%)

Element	Requirement
Carbon	0.08 max
Manganese	2.00 max
Phosphorus	0.045 max
Sulfur	0.030 max
Silicon	1.00 max
Chromium	18.00 - 20.00
Nickel	8.00 - 11.00

Mechanical properties and hardness

The guaranteed mechanical properties of TP304 in the heat-treated condition per ASTM A213: tensile strength 515 MPa min, yield strength 205 MPa min, elongation 35% min (in 2 in or 50 mm). Hardness limits are 192 HBW, 90 HRB or 200 HV.

Property	Minimum value
Tensile strength	515 MPa
Yield strength	205 MPa
Elongation (2 in)	35%
Hardness	192 HBW / 90 HRB / 200 HV max

Heat treatment

TP304 U-tubes are supplied in the solution-annealed condition: heated to a minimum temperature of 1040 degree C and rapidly cooled in water or by other rapid cooling methods. After cold bending, the U-bend region may be re-solution annealed or stress relieved depending on the bend radius, wall thickness and the requirements of the applicable heat-exchanger standard such as TEMA or ASME Section VIII.

In U-bend manufacturing, the bend radius is selected from the tube outside diameter, commonly 1.5D, 2D or 3D. After bending, the tube is checked for ovality, wall thinning at the extrados and wrinkling at the intrados. Eddy current or hydrostatic testing, dimensional gauging and dye penetrant examination of the bend zone are typical acceptance checks. The heat-affected bend area must remain within the hardness and mechanical limits of the standard.

Equivalent designations

Standard	Grade designation
ASTM A213	TP304 / UNS S30400
GB	06Cr19Ni9
JIS G3463	SUS304TP
ISO	X5CrNi18-10
GOST 9941	08X18H10

Typical applications

TP304 U-tubes are used in shell-and-tube heat exchangers, condensers, coolers and heater bundles in chemical, petrochemical, food processing, HVAC and power auxiliary systems, where clean service media allow the use of the general-purpose 18-8 grade.

Frequently asked questions

Q1: What is the difference between TP304 and TP304L? A1: TP304L (UNS S30403) limits carbon to 0.035% max for improved resistance to sensitization in welded service; TP304 is the standard-carbon grade with slightly higher elevated-temperature strength.

Q2: What bend radius is typical for U-tubes? A2: Common centerline bend radii are 1.5D, 2D and 3D of the tube outside diameter; tighter radii require special bending qualification.

Q3: Is heat treatment required after bending? A3: When the bend is made from solution-annealed tube and the bend radius is within the qualified range, no additional heat treatment is required; the bend zone must still meet the hardness limits of the standard.

Q4: What tests apply to TP304 U-tubes? A4: Typical acceptance tests include chemical analysis, tensile testing, flattening and flaring tests, hydrostatic or eddy current testing, and dimensional inspection of the bend zone.

Q5: What service temperature is TP304 suitable for? A5: For aqueous service, roughly -196 to 400 degree C depending on pressure; at higher temperatures the design must consider the reduced allowable stresses and the risk of sensitization in the 450-850 degree C range.