What are the specifications of SS 347H Seamless Pipe?

Available in UNS S34709 (ASTM A312 TP347H), OD 1/8"-24" NB, Sch 5S-160, hot finished or cold drawn seamless construction, carbon controlled at 0.04-0.10%.

Why choose 347H over standard 347?

347H's higher carbon content increases creep strength and allowable design stress at elevated temperatures, important in high-pressure supercritical steam applications governed by ASME Section I.

Is 347H prone to sensitization given its higher carbon content?

The niobium addition scales with carbon content, so it remains effective at locking up the extra carbon as stable carbides, preserving corrosion resistance despite the higher carbon ceiling.

Where is 347H specifically mandated over 321H?

Ultra-supercritical boiler superheater/reheater sections often specify 347H by name due to its superior long-term creep-rupture data at the highest steam temperatures used in modern high-efficiency plants.

Does Sakshi Forge provide Material Test Certificates (MTC) for SS 347H Seamless Pipe?

Yes, MTC as per EN 10204 3.1 is provided with every dispatch along with inspection reports.

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SS 347H Seamless Pipe - High Carbon Niobium-Stabilized Pipe | Sakshi Forge

High-Carbon Niobium-Stabilized Pipe for Supercritical Boiler Headers and Steam Piping

Controlled carbon window (0.04-0.10%) for maximum creep-rupture strength under ASME Section I

Niobium stabilized against sensitization despite higher carbon ceiling

Standard specification for ultra-supercritical thermal power steam headers and superheaters

EN 10204 3.1 MTC100% PMI TestedISO 9001:2015 CertifiedHydrostatic Tested

Hygienic Steel Grade

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MTC EN 10204 3.1 Included

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Response turnaround: Under 2 hours

Product Profile

SS 347H (UNS S34709 / ASTM A312 TP347H) is a high-carbon variant of niobium-stabilized stainless steel seamless pipe specifically formulated for maximum creep and stress-rupture strength in elevated-temperature pressure piping. The carbon content is strictly controlled within a higher window of 0.04% to 0.10% (compared to 0.08% max for standard 347). Proportional niobium alloying (Nb 8xC to 1.00% max) locks this carbon into fine, thermally stable niobium carbides, enhancing elevated-temperature creep strength without compromising post-weld corrosion resistance. SS 347H is the premier material choice for ASME Section I ultra-supercritical (USC) power boiler superheaters, reheaters, and high-pressure steam transfer lines operating between 538°C and 816°C (1000°F to 1500°F). Sakshi Forge manufactures SS 347H seamless pipes using precision hot extrusion and cold drawing, backed by stringent solution annealing above 1060°C to ensure full carbide solutioning and optimal high-temperature allowable stress values.

Terminology & Abbreviations

UNS S34709|S34709

Werkstoff 1.4912|1.4912

ASTM A312 TP347H|TP347H

ASME SA312 TP347H|TP347H

Key Technical Facts

Carbon controlled between 0.04% and 0.10% to maximize high-temperature creep strength

Niobium added at minimum 8x carbon (up to 1.00% max) to bind extra carbon as NbC carbides

Delivers the highest allowable design stress among 18-8 series stainless grades under ASME B31.3 / Section I

Resists sensitization and intergranular attack during prolonged elevated temperature steam exposure

Heat treated via solution annealing at a minimum temperature of 1060°C (1940°F) followed by rapid quench

Hot extruded and cold drawn seamless construction per ASTM A312 Grade TP347H

100% hydrotested per ASTM A999 and Eddy Current / Ultrasonic non-destructive flaw checked

Supplied with full EN 10204 3.1 certification and ASME boiler code heat traceability

Why Choose Sakshi Forge

Our commitment to sterile, high-purity processing makes us a trusted manufacturing partner globally.

100% Heat Lot Traceability

Every pipe stamped with heat number matching EN 10204 3.1 MTC

Positive Material Identification (PMI)

Handheld XRF testing on every length prior to dispatch

Advanced NDT Inspection

Hydrostatic test and Eddy Current / Ultrasonic flaw detection on all orders

Precision Cold Drawing

Tighter wall thickness tolerances and superior internal bore smoothness

Custom Cut Lengths

Fixed lengths up to 12 meters or custom cut-to-length options to eliminate jobsite scrap

Ferrite & Phase Balance Testing

Ferritescope testing for duplex and super duplex grades to ensure 40-60% phase balance

High-Temperature Stabilization

Controlled heat treatment to fully precipitate carbides and optimize creep life

Pan-India & Export Freight

Fast dispatch across India and seaworthy export packing for global projects

Extensive Mill Stocking

Immediate inventory availability in standard schedules from Sch 10S to Sch 160

Third-Party Inspection Approved

Full support for TUV, SGS, DNV, Bureau Veritas, and Lloyds audits

Frequently Asked Questions

Common technical and pricing queries regarding specifications and ordering.

SS 347H seamless pipe is specified under UNS S34709 / ASTM A312 TP347H. It features controlled carbon (0.04-0.10%) and niobium stabilization (Nb 8xC min) for high-pressure steam piping.

Partner with Sakshi Forge for Reliable Industrial Steel Solutions

Delivering precision-engineered flanges, pipes, and forged steel components designed for strength, durability, and performance in critical high-pressure industrial applications.