347 vs. 347H vs. 347HFG: Key Differences
Jul 06, 2026
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347 vs. 347H vs. 347HFG: Key Differences
Choosing between 347, 347H, and 347HFG stainless steel directly affects equipment service life, creep resistance, welding performance, and compliance with ASME boiler and pressure vessel requirements. Selecting the wrong grade may result in premature creep failure, increased maintenance costs, or rejection during project inspection.
What is 347 stainless steel?
347 stainless steel is a niobium (columbium) stabilized austenitic stainless steel. It features a maximum carbon content of 0.08% and is suitable for general corrosion resistance as well as moderate-temperature environments up to approximately 800°F (427°C). It is widely used in heavy welded equipment, aircraft exhaust systems, high-temperature chemical processing, and pressure manufacturing industries.
What is 347H material?
347H stainless steel is the high-carbon version of the alloy, requiring a carbon content between 0.04% and 0.10%. This higher carbon level significantly enhances creep strength and stress-rupture properties, making it ideal for ASME-regulated pressure vessel components operating at temperatures above 1000°F (540°C).
What is 347HFG stainless steel?
347HFG is a highly durable, niobium-stabilized austenitic stainless steel specifically engineered for high-temperature service. The "H" in the grade designation indicates a controlled carbon content meant to provide superior creep resistance, while "FG" stands for "Fine Grain." This fine-grain structure delivers superior high-temperature fatigue strength and ductility while improving formability. It is particularly well-suited for complex superheater and reheater tubes in ultra-supercritical boilers.
ASTM A213 TP347 / TP347H / 347HFG Stainless Steel Tubes Chemical Composition
| Grade | 347 | 347H | 347HFG |
| UNS Designation | S34700 | S34709 | S34710 |
| Carbon (C) Max. | 0.08 | 0.04–0.10 | 0.06–0.10 |
| Manganese (Mn) Max. | 2.00 | 2.00 | 2.00 |
| Phosphorous (P) Max. | 0.04 | 0.04 | 0.04 |
| Sulphur (S) Max. | 0.03 | 0.03 | 0.03 |
| Silicon (Si) Max. | 0.75 | 0.75 | 0.75 |
| Chromium (Cr) | 17.0–20.0 | 17.0–20.0 | 17.0–20.0 |
| Nickel (Ni) | 9.0–13.0 | 9.0–13.0 | 9.0–13.0 |
| Molybdenum (Mo) | - | - | |
| Nitrogen (N) | - | - | - |
| Iron (Fe) | Bal. | Bal. | Bal. |
| Niobium(Nb) | 10xC-1.10 | 8xC-1.10 | 8xC-1.10 |
What is the difference between 347 and 347H?
The primary difference between 347 and 347H stainless steel is their carbon content. Grade 347 is a niobium-stabilized austenitic stainless steel with a maximum carbon content of 0.08%, while 347H is the high-carbon version (0.04% to 0.10%) designed specifically for superior high-temperature strength and creep resistance.
A213 TP347 TP347H 347HFG Stainless Steel Mechanical Properties
| Tensile Strength | Tensile Strength | Yield Strength | Yield Strength | ||||||
| Alloy | UNS | Spec | MPa | ksi | MPa | ksi | Elongation in 2 inches (min.) % | Grain Size Req. | Harndess HBW |
| 347 | S34700 | ASTM A213 |
515 | 75 | 205 | 30 | 35 | - | 192 |
| 347H | S34709 | ASME SA 213 | 515 | 75 | 205 | 30 | 35 | 7 or coarser | 192 |
| 347HFG | S34710 | - | 550 | 80 | 205 | 30 | 35 | 7 or coarser | 192 |
347 vs. 347H vs. 347HFG: High Temperature
| Property | 347 Stainless Steel | 347H Stainless Steel | 347HFG Stainless Steel |
|---|---|---|---|
| Maximum Continuous Service Temperature | Up to 870°C (1600°F) | Up to 900°C (1650°F) | Up to 950°C (1740°F) |
| Recommended Long-Term Operating Temperature | ≤ 550°C | 550–750°C | 600–850°C |
347 vs. 347H vs. 347HFG: Corrosion Resistance
Grades 347, 347H, and 347HFG exhibit comparable resistance to intergranular corrosion in both annealed and welded conditions. Although grades 347H and 347HFG have higher carbon content ranges (0.04%–0.10% versus ≤0.08% for grade 347), the mandatory requirement for excess niobium ensures that sufficient free chromium remains to maintain the passive film. Consequently, under standard operating conditions, there is no significant difference in their susceptibility to weld decay or sensitization.
347 vs. 347H vs. 347HFG: Industry Applications
| Industry Sector | AISI 347 (Standard) | AISI 347H (High Carbon) | 347HFG (Fine Grain) |
| Power Generation | Low-pressure boiler components and support structures. | Superheater and Reheater tubes in conventional coal-fired power plants. | Ultra-Supercritical (USC) power plant boiler tubes (High-pressure/High-heat). |
| Oil & Gas / Refinery | Fluid Catalytic Cracking (FCC) units, hydrocracker tubes. | Furnace tubes, distillation units, and high-temp piping systems. | Specialized high-pressure hydrogen service and heavy oil upgrading. |
| Aerospace | Aircraft exhaust manifolds, jet engine parts, and collector rings. | Rocket engine components and high-heat structural fasteners. | (Rarely used in aerospace; focused on steam environments). |
| Chemical Processing | Reactor vessels, storage tanks for organic chemicals/acids. | High-temperature chemical reactors and heat exchanger shells. | Specialized high-temp chemical piping where steam oxidation is a risk. |
| Automotive | Heavy-duty truck exhaust systems and catalytic converter housings. | High-performance racing exhaust headers. | (Not standard for automotive). |
How to Choose Between 347, 347H and 347HFG?
If your project involves continuous service above 600°C or falls under ASME Section I or high-temperature power generation specifications, 347H or 347HFG is generally recommended over standard 347. For the most demanding creep-service applications with extended design life, 347HFG offers the best long-term performance despite its higher material cost.
347, 347H, and 347HFG Stainless Steel Heat Exchanger Tubes Supplier
GNEE Stainless Steel is a specialized manufacturer of stainless steel heat exchanger tubes, producing grades such as ASME SA213 TP347/TP347H, ASTM A312 347/347H, ASTM A213 347H (seamless), and EN 10216-5 (grades 1.4550/1.4912). We manufacture seamless tubes, U-tubes, and coiled tubing in SA213 TP347/TP347H specifications, with an outer diameter range of 6–530 mm, wall thickness of 0.5–30 mm, and lengths up to 25,000 mm. Please send us an inquiry for further details. We maintain extensive stock of 347/347H stainless steel tubes in China to support urgent projects.
Packaging
All our seamless stainless steel pipes are packaged in accordance with international standards to prevent any potential damage or loss. By default, we bundle the finished pipes together in batches using heavy-duty woven plastic bags.
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