TP347H Seamless Stainless Steel Tube

UNS S34709 | 1.4912 | ASTM A213

TP347H Seamless Stainless Steel Tube (S34709 / 1.4912) is manufactured to ASTM A213 from stainless steel billet, cold-drawn to the required outside diameter and wall thickness. Supplied from our Wenzhou mill with EN 10204 3.1 mill test certificate, PMI and dimensional inspection on request.

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What Is a Seamless Stainless Steel TP347H Tube?

TP347H (UNS S34709) is a niobium-stabilised, high-carbon austenitic stainless steel tube for elevated-temperature service. The carbon range of 0.04–0.10% combined with niobium stabilisation delivers high creep-rupture strength and resistance to intergranular corrosion, while the chromium and nickel contents provide the oxidation resistance expected of an 18-8 grade.

Seamless Stainless Steel TP347H Tube-ASTM A213 TP347H (UNS S34709) | High-Temperature Niobium-Stabilized Tubing

ASTM A213 TP347H Seamless Stainless Steel Tube (UNS S34709) is a high-carbon, niobium-stabilized austenitic stainless steel tube designed for high-temperature and high-pressure service environments.

These properties make TP347H the preferred material for boilers, superheaters, and heat exchangers operating above 538°C (1000°F).

TP347H Key Features and Technical Advantages

Feature	Description
Niobium Stabilisation	Niobium at 8 × C to 1.00% forms stable NbC, preventing chromium depletion at grain boundaries and preserving intergranular corrosion resistance.
High Creep-Rupture Strength	The 0.04–0.10% carbon range combined with niobium gives TP347H excellent creep and stress-rupture strength for high-temperature headers and superheaters.
Excellent Oxidation Resistance	18% chromium provides a protective oxide appropriate for continuous service up to about 800 °C.
Resistance to Polythionic Acid Stress Corrosion	Stabilisation specifically protects against polythionic acid SCC, the failure mode that governs refinery heater tubing.
Good Fabricability and Weldability	TP347H is readily formed and welded, with matching stabilised filler available for critical joints.

TP347H Product Specifications and Data

The composition of Stainless Steel 347H is carefully balanced to achieve its superior high-temperature strength and corrosion resistance.

Grade	C	Cr	Ni	Mn	P	S	Si	Others
347	≤0.08	17.00-20.00	9.00-13.00	≤2.00	≤0.045	≤0.030	≤1.00	Nb≥10*C%
347H	0.04-0.10	17.00-19.00	9.00-13.00	≤2.00	≤0.045	≤0.030	≤1.00	Nb≥8*C%

Note: The niobium content must be at least eight times the carbon content to ensure stabilization.

Stainless Steel 347H is specifically designed to maintain its strength and shape in high-temperature, high-stress environments.

Grade	Yield strength ksi(MPa)	Tensile Strength ksi(MPa)	Elongation %	Hardness Brinell/Vickers	Hardness Rockwell
347	≥30(205)	≥75(515)	≥35	≤192 HBW/200HV	≤90HRB
347H	≥30(205)	≥75(515)	≥35	≤192 HBW/200HV	≤90HRB

These physical properties highlight the material's ability to perform reliably under a wide range of conditions.

Density	Melting Point	Thermal Expansion	Thermal Conductivity	Modulus of Elasticity	Electrical Resistivity
8.0 g/cm³	1398 - 1454 °C	16.6 µm/m·°C (20-100°C)	16.3 W/m·K (20°C)	193 GPa	0.72 x 10⁻⁶ Ω·m (20°C)

Standard	OD(D)	Tolerance（MM)		Thickness(S)	Tolerance(MM)	Length	Tolerance
Standard	MM	Common	High	MM	Tolerance(MM)	Length	MM
EN 10216-5 HFD	30≤D≤219.1（D2)	±1.0% or ±0.5mm, whicever is the greater		T1, T≤4	±15% or ±0.6mm, whicever is the greater	L≤6M	+5/0
	30≤D≤219.1（D2)	±1.0% or ±0.5mm, whicever is the greater		T2	±12.5% or ±0.4mm, whicever is the greater	L≤6M	+5/0
	219.1≤D≤610 (D1)	±1.5% or ±0.75mm, whicever is the greater		T≤0.05D	+22.5%/-15%	6＜l≤12	+10/0
				T1, 0.05D＜t≤0.09D	±15% or ±0.6mm, whicever is the greater	6＜l≤12	+10/0
				T2, T>0.09D	±12.5% or ±0.4mm, whicever is the greater	L>12	+by agreement/0
EN 10216-5 CFD	D3(D≤219.1)	±0.75% or ±0.3mm, whicever is the greater		T3	±10% or ±0.2mm, whicever is the greater
EN 10216-5 CFD	D4(D≤219.1)	±0.5% or ±0.mm, whicever is the greater		T4	±7.5% or ±0.15mm, whicever is the greater
ASTM A213 HFD	D≤100	+0.4/-0.8		D＜100,S≤2.4	+40%/0	HFD, all size	+5.0/0
		+0.4/-1.2		D＜100,2.4＜s≤3.8	+35%/0
		+0.4/-1.6		D＜100,3.8＜s≤4.6	+33%/0
		+0.4/-1.6		D＜100,S>4.6	+28%/0
	100＜d≤200	+0.4/-1.2		D>100, 2.4＜s≤3.8	+35%/0
	200＜d≤225	+0.4/-1.6		D>100,3.8＜s≤4.6	+33%/0
	200＜d≤225	+0.4/-1.6		D>100,S>4.6	+28%/0
ASTM A213 CFD	D＜25	±0.10		D≤38.1	+20%/0	CFD, D＜50.8	+3.0/0
	25≤D≤40	±0.15
	40＜d＜50＜ span="">	±0.20
	50≤D＜65	±0.25
	65≤D＜75	±0.30		D>38.1	+22%/0	CFD, D≥50.8	+5.0/0
	75≤D≤100	±0.38
	100＜d≤200	+0.38/-0.64
	200＜d≤225	+0.38/-1.14
ASTM A269	D≤13	±0.13		D≤13	±15%	D＜38	+3.2/0
	13＜d＜38＜ span="">	±0.13		13＜d＜356＜ span="">	±10%	D＜38	+3.2/0
	38≤D＜89	±0.25				D>38	+4.8/0
	89≤D＜140	±0.38
	140≤D＜203	±0.76
	203≤D＜305	±1.01
	305≤D＜356	±1.26
ASTM A270	D＜25	±0.13		For weld pipe all size	±12.5%		+3.0/0
	25-50	±0.20
	50-75	±0.25
	75-100	±0.38		For CD SMLS pipe D≤38.1	+20%/0
	100-140	±0.38		For CD SMLS pipe D≤38.1	+20%/0		+5.0/0
	140-200	±0.75		For CD SMLS pipe D>38.1	+22%/0
	200-300	±1.25		For CD SMLS pipe D>38.1	+22%/0

TP347H Dimensional Standards and Tolerances

TP347H seamless tubes are supplied to the dimensional tolerances of ASTM A213 / A1016 unless a tighter project specification applies.

Typical Applications of TP347H Seamless Tubes

TP347H tubes are widely used in high-temperature, high-pressure, and corrosion-intensive industries:

Industry	Typical Applications
Power Generation	Superheater and reheater tubes Ultra-supercritical (USC) boilers
Petrochemical & Refining	Hydrocracking units Hydrotreating systems High-temperature hydrogen service
Renewable Energy	Biomass boilers Waste-to-energy incinerators
Chemical Processing	Heat exchangers Acid-resistant high-temperature piping systems

Why Choose Our TP347H Seamless Tubes?

Item	Description
Stable Supply	Stable supply with strict quality control.
Competitive Pricing	Competitive stock pricing.
Certification & Inspection	Full certification and third-party inspection support.
Fast Delivery	Fast delivery for global projects.

Industry	Typical Applications
Refinery and Petrochemical Heaters	Heater and furnace tubing Transfer and process lines Polythionic-acid service piping
Power Generation	Superheater and reheater tubing Main steam and hot reheat piping Boiler pressure parts
High-Temperature Process Plant	Creep-critical headers Heat exchanger tubing Expansion and transition joints
Chemical Processing	High-temperature reactor internals Process piping Heat-transfer equipment

TP347H Quality Assurance and Production Process

Process Step	Description
Certification	All TP347H tubes are supplied to ASTM A213 / ASME SA213 and ASTM A312 / ASME SA312 with EN 10204 3.1 mill test certificates. Third-party inspection (SGS, BV, TUV, Lloyd's), PMI reports and full heat-number traceability can be provided on request.
Non-Destructive Testing (NDT)	Hydrostatic or eddy-current testing is performed on 100% of tubes. Ultrasonic testing (UT) and dye-penetrant inspection (PT) are available for critical service, with records retained for each production lot.
Material Verification	Positive Material Identification (PMI) and spectrometric analysis confirm that the chemical composition matches the ordered grade. Intergranular corrosion (IGC) testing to ASTM A262 Practice E is available for austenitic and nickel-alloy tubes.
Mechanical Testing	Tensile, yield, elongation and hardness tests are carried out per heat. Flattening, flaring and reverse-bend tests verify ductility, while creep-rupture data can be supplied for high-temperature grades.
Dimensional Inspection	Outside diameter, wall thickness, ovality and straightness are measured against ASTM A1016 / A1016M or EN 10216-5 tolerances. Length, square-cut ends and end-finish conditions are verified before packing.

TP347H vs TP347 / TP321H – Technical Comparison

TP347H and TP347 share a niobium-stabilised 18-8 base, while TP321H uses titanium instead. The choice between them turns on creep strength and on which stabiliser suits the fabrication route.

Stabiliser and Carbon Content

TP347H: niobium-stabilised, 0.04–0.10% C
TP347: niobium-stabilised, 0.08% C maximum
TP321H: titanium-stabilised, 0.04–0.10% C

Creep-Rupture Strength

The controlled high-carbon range of TP347H delivers creep-rupture strength that the standard TP347 cannot match at the same temperature. This is why TP347H is the default for superheater and reheater tubing in modern boilers.

Polythionic Acid Stress-Corrosion Resistance

Both niobium and titanium stabilisation protect against polythionic acid SCC, the failure mode that governs refinery heater tubing. Niobium-stabilised grades are often preferred in refinery service where the stabiliser must survive high-temperature exposure.

Selection Guide

Choose TP347H for creep-limited superheater and reheater tubing
Choose TP321H where titanium stabilisation is specified
Choose TP347 where creep strength is not the governing requirement

Frequently Asked Questions About TP347H Seamless Stainless Steel Tubes

What is TP347H seamless tube?

TP347H (UNS S34709) is a niobium-stabilised austenitic stainless steel tube with carbon controlled in the 0.04–0.10% range, produced without a longitudinal weld. It is designed for elevated-temperature service where creep strength governs.

Why is TP347H stabilised with niobium?

Niobium at 8 × C to 1.00% forms stable niobium carbides, which prevents chromium carbide precipitation at grain boundaries. This preserves intergranular corrosion resistance and specifically protects against polythionic acid stress-corrosion cracking.

What is the difference between TP347 and TP347H?

TP347 permits up to 0.08% carbon, while TP347H controls carbon in the 0.04–0.10% range. The higher, controlled carbon content of TP347H delivers significantly better creep and stress-rupture strength at elevated temperature.

What is TP347H tube used for?

TP347H is used for superheater and reheater tubing, refinery heater tubing, high-temperature process piping and creep-limited headers in power and petrochemical plants.

Request a TP347H Tube Quotation

Send your Seamless Stainless Steel TP347H Tube enquiry with grade, application, size (OD and wall thickness or schedule), quantity, length, end finish and inspection requirements. Our technical team will confirm availability, testing scope and lead time.

Request a TP347H Tube Quotation