S347h Pipe

S347H (UNS S34709) is a high-carbon, niobium-stabilized austenitic stainless steel. To understand its unique field performance, it helps to compare it directly to its closest structural relatives. Our manufacturers can produce seamless and welded pipes to meet industry requirements. Contact us market@htpipe.com for more information and a free quote!

Product Forms

Bar & Rod

Plate & Sheet

Coil & Strip

Pipe & Tube

Fitting: Flange, Tee, Elbow, Reducer etc.

Forging: Ring, Shaft, Circle, Block etc.

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Elevated Temperature Mechanics

The "H" designation in S347H denotes its high carbon content. While low carbon is traditionally preferred to limit corrosion during welding, elevated carbon is crucial for high-temperature mechanical properties.

Creep Strength and Stress Rupture

In critical power plant piping and refinery systems, metals under sustained stress at high temperatures undergo gradual, permanent deformation over time-a process called creep.

S347H delivers more than twice the creep rupture strength of standard 304H or 316H at temperatures exceeding 700°C (1292°F).

The uniform distribution of NbC precipitates provides strong lattice pinning, preventing the micro-structural slippage that leads to creep failure.

Oxidation and Scaling Resistance

Continuous thermal cycling can cause protective oxides on less resilient steels to spall, leading to accelerated thinning of pipe walls. S347H exhibits stable oxidation and scaling resistance up to continuous operating limits of 750°C (1382°F), with short-term excursion tolerances reaching up to 900°C (1652°F).

Manufacturing Standards and Processing Guidelines

Global Industry Specifications

S347H pipes are manufactured under strict international standards depending on the final application:

ASTM A312 / ASME SA312: Specifies seamless, straight-seam welded, and heavily cold-worked welded austenitic pipes intended for high-temperature and general corrosive service.

ASTM A213 / ASME SA213: Covers seamless ferritic and austenitic steel boiler, superheater, and heat-exchanger tubes.

ASTM A358 / ASME SA358: Governs Electric-Fusion-Welded (EFW) pipes designed for high-pressure configurations.

Heat Treatment Protocol

Achieving optimal mechanical characteristics requires precise thermal processing:

Solution Annealing: The material must be heated within the range of 1925°F to 2000°F (1050°C to 1100°C), followed by a rapid water quench or forced air cool to prevent secondary phase precipitates.

Stabilization Heat Treatment: Often specified for extreme severe-service environments, this process heats the pipe to roughly 1600°F–1650°F (870°C–900°C). This maximizes niobium carbide precipitation prior to field service, fully ensuring that subsequent lower-temperature exposures cannot trigger sensitization.

Application uns s34709 pipe

Oil and gas: submarine pipelines, downhole tools for acid gas wells.

Chemical equipment: sulfuric acid reactors, phosphoric acid evaporators, pickling equipment.

Nuclear industry: containers and pipelines for nuclear waste treatment systems.

Marine engineering: seawater desalination devices, heat exchangers.

Environmental protection: key components of flue gas desulfurization (FGD) systems.

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