TP347 Seamless Stainless Steel Tube

UNS S34700 | 1.4550 | ASTM A213

TP347 Seamless Stainless Steel Tube (S34700 / 1.4550) 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 TP347 Tube?

TP347 (UNS S34700) is a niobium-stabilised austenitic stainless steel tube based on the 18-8 composition. Niobium at 8 × C to 1.00% ties up carbon as stable niobium carbides, preventing chromium carbide precipitation at grain boundaries and thereby preserving intergranular corrosion resistance after welding and in intermediate-temperature service.

Seamless TP347 stainless steel tube (UNS S34700 / W.Nr. 1.4550) is a niobium (columbium) stabilized austenitic stainless steel tube designed for applications involving high temperatures and intergranular corrosion resistance.

Produced through a seamless process (hot piercing + cold drawing/finishing) from a solid billet, TP347 tubes provide:

The key feature of TP347 is the addition of Niobium (Nb), which stabilizes carbon and prevents chromium carbide precipitation at grain boundaries. This ensures superior resistance to sensitization and intergranular corrosion (IGC), even after prolonged exposure to elevated temperatures or welding.

TP347 Key Features and Technical Advantages

Excellent Intergranular Corrosion Resistance Niobium stabilization prevents carbide precipitation, eliminating sensitization in the heat-affected zone (HAZ).

High-Temperature Performance (Up to 815°C) Performs reliably in continuous service up to 815°C (1500°F) with strong oxidation and scaling resistance.

Improved Creep Strength Compared with standard 304/304L, TP347 offers better creep resistance and structural stability under long-term high-temperature stress.

Feature	Description
Excellent Intergranular Corrosion Resistance	Niobium stabilization prevents carbide precipitation, eliminating sensitization in the heat-affected zone (HAZ).
High-Temperature Performance (Up to 815°C)	Performs reliably in continuous service up to 815°C (1500°F) with strong oxidation and scaling resistance.
Improved Creep Strength	Compared with standard 304/304L, TP347 offers better creep resistance and structural stability under long-term high-temperature stress.
Excellent Weldability	Can be welded using standard methods without requiring post-weld heat treatment to restore corrosion resistance.
High Pressure Integrity	Seamless production ensures compliance with ASTM A213 / ASME SA213 / EN 10216-5, suitable for critical pressure systems.

TP347 Product Specifications and Data

To provide a comprehensive overview of this high-performance material, here are the detailed technical specifications and performance data for Stainless Steel 347.

The composition of Stainless Steel 347 is carefully balanced to achieve its superior high-temperature stability 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 ten times the carbon content to ensure stabilization.

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

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

TP347 Dimensional Standards and Tolerances

TP347 seamless tubes are supplied to the dimensional tolerances of ASTM A213 / A1016 unless a tighter project specification applies.

TP347 Common Industrial Applications

Industry	Typical Applications
Power Generation	Superheater and reheater tubing Boiler pressure parts High-temperature piping
Aerospace and Energy Systems	High-temperature exhaust components Heat exchanger tubing Specialty energy equipment
Petrochemical and Refinery	Heater and furnace tubing Process and transfer lines Polythionic-acid service piping
Waste and Incineration	Incinerator heat recovery tubing Waste-heat boiler components Flue-gas handling equipment

TP347 Quality Assurance and Production Process

Process Step	Description
Certification	All TP347 (UNS S34700) 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 and that the ferrite/austenite balance is within the specified range.
Mechanical Testing	Tensile, yield, elongation and hardness tests are carried out per heat. Impact testing can be supplied at the project design temperature for subsea and low-temperature service.
Dimensional Inspection	Outside diameter, wall thickness, ovality and straightness are measured against ASTM A1016 / A1016M or ASTM A789 tolerances. Length, square-cut ends and end-finish conditions are verified before packing.

TP347 vs TP321 / TP347H – Technical Comparison

TP347,TP321 and TP347H are all stabilised austenitic grades used at elevated temperature. The choice between them turns on the stabiliser and the carbon content.

Stabiliser and Carbon Content

TP347: niobium-stabilised (8 × C to 1.00%), carbon 0.08% maximum
TP321: titanium-stabilised (5 × C to 0.70%), carbon 0.08% maximum
TP347H: niobium-stabilised with carbon 0.04–0.10% for creep strength

Elevated-Temperature Strength

TP347H delivers the highest creep-rupture strength of the three because of its controlled high-carbon range. TP347 and TP321 are comparable to each other, with niobium-stabilised grades generally preferred where high-temperature exposure follows welding.

Intergranular Corrosion Resistance

All three resist intergranular corrosion because the stabiliser ties up carbon as stable carbides. TP347 and TP347H also resist polythionic acid stress-corrosion cracking, which is the failure mode that governs refinery heater tubing.

Selection Guide

Choose TP347 for welded equipment needing stabilisation at moderate temperature
Choose TP347H for creep-limited superheater and heater tubing
Choose TP321 where titanium stabilisation is specified

Frequently Asked Questions About TP347 Seamless Stainless Steel Tubes

What is TP347 tube?

TP347 (UNS S34700) is a niobium-stabilised austenitic stainless steel tube based on the 18-8 composition. Niobium ties up carbon as stable carbides, preventing chromium carbide precipitation at grain boundaries.

Why is TP347 stabilised with niobium?

Stabilisation preserves intergranular corrosion resistance in the heat-affected zone after welding and in intermediate-temperature service, and specifically protects against polythionic acid stress-corrosion cracking, the failure mode that governs refinery heater tubing.

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 controlled higher carbon content of TP347H delivers significantly better creep and stress-rupture strength at elevated temperature.

What is TP347 tube used for?

TP347 serves in power generation boiler and superheater components, petrochemical heater and process tubing, aerospace and energy systems, and waste incineration equipment.

Request a TP347 Tube Quotation

Send your Seamless Stainless Steel TP347 Tube enquiry with grade, application, size (OD and wall thickness or schedule), quantity, length, end finish and inspection requirements including any intergranular corrosion test data required.

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