Detailed introduction of 347H stainless steel pipe

347H stainless steel pipe is a type of austenitic stainless steel pipe with high carbon and niobium (Nb) content. Due to its excellent high-temperature performance, corrosion resistance and welding properties, it plays a crucial role in the fields of energy, chemical industry, aerospace, etc. The following provides a detailed analysis from the aspects of composition, performance, application and processing. 

I. Chemical Composition and Microscopic Structure 

Main alloying elements

Carbon (C: 0.04 - 0.10%), chromium (Cr: 17 - 19%), nickel (Ni: 9 - 13%), niobium (Nb: 8C - 1.10%), silicon (Si ≤ 0.75%), manganese (Mn ≤ 2.00%). Among them, niobium combines with carbon to form carbide niobium (NbC), effectively inhibiting the precipitation of chromium carbides at the grain boundaries, significantly enhancing the intergranular corrosion resistance.

Microstructure

After solution treatment (1000 - 1100℃ water cooling), a single austenite structure is formed, with excellent high-temperature stability. The addition of niobium makes carbides less likely to aggregate at high temperatures, thus maintaining the material's long-term strength. 

II. Core Performance Analysis

1. High Temperature Mechanical Properties Intensity

Tensile strength ≥ 515 MPa, yield strength ≥ 205 MPa, elongation ≥ 35% (in accordance with ASTM A213 standard). At 600°C, its allowable stress can still reach above 100 MPa, which is superior to 304H stainless steel.

Antioxidant property

In air at 750-800°C, it has stable antioxidant properties, and the maximum antioxidant temperature can reach 850°C (for non-pressure-bearing components), suitable for high-temperature environments such as boiler superheaters.

Creep resistance

During long-term service at 550-700°C, the creep fracture strength of 347H is approximately 15% higher than that of 321H, making it more suitable for high-temperature pipelines in supercritical power plants.

2. Corrosion resistance

Intergranular corrosion

The stabilizing effect of niobium enables it to maintain excellent intergranular corrosion resistance after welding, which is superior to 304 stainless steel without stabilizing elements.

Corrosion resistance to media

It performs well in nitric acid, acetic acid, alkaline solutions and seawater, but has slightly higher pitting corrosion sensitivity to chloride environments than 316L, which can be alleviated by surface treatment or controlling the concentration of chloride ions in the environment.

Solute salt corrosion

The 347H stainless steel developed by Shijiazhuang Iron and Steel Group performs exceptionally well in molten salt storage tanks of photothermal power plants. Its solute salt corrosion resistance has been verified through laboratory simulation and has been batch-applied to multiple national-level photothermal projects.

3. Processing and welding properties

Cold processing

When cold forming, attention should be paid to the hardening effect of processing. It is recommended to use multi-pass forming and appropriate intermediate annealing (850-900°C). Welding

It is recommended to use welding wires containing niobium (such as ER347), and avoid titanium-stabilized welding wires (such as ER321) as titanium loss may cause weld cracking. The TGF-347 argon-free welding wire enables self-protection welding on the backside, thereby improving the on-site construction efficiency. Heat treatment

The solution treatment temperature is 980 - 1150℃, and rapid water cooling is used to prevent the formation of carbides. For thick-walled pipe fittings, the heating speed needs to be controlled to avoid deformation. 

III. Typical Application Scenarios

1. Power Industry

Power Station Boiler

High-temperature superheaters, reheaters, main steam pipelines (pressure-bearing components below 650℃), such as Φ51×8mm 347H steel pipes in projects like Huaneng Jinggangshan Power Plant and Datang Yangcheng Power Plant, have been operating stably for many years.

Solar Thermal Power Generation

347H stainless steel plates for molten salt storage tanks have cumulatively supplied over 7,000 tons, applied in solar thermal projects such as Yumen and Haixi, capable of withstanding 450-565℃ high-temperature molten salt corrosion.

2. Petrochemical Industry

Cracking Furnace Tubes

Tolerating 800℃ high temperature and hydrocarbon medium corrosion in ethylene cracking furnaces.

Hydrogenation Reactors

Used in hydrogenation refining units, resistant to hydrogen sulfide - hydrogen - water corrosive environments.

3. Aerospace

Engine Components

Such as turbine compressor hot gas pipelines, capable of withstanding small loads below 850℃.

Exhaust Systems

Resistant to corrosion from aviation fuel combustion products. 

IV. Comparison with Similar Materials

Picture (Figure 1) 

V. Standards and Manufacturing Processes

1. Execution Standards

International Standards

ASTM A213/SA213 (Unalloyed Seamless Pipes for Boilers and Heat Exchangers), EN 10216-5 (Pressure-bearing Seamless Steel Pipes).

Chinese Standards

GB/T 5310 (Unalloyed Seamless Pipes for High-Pressure Boilers), corresponding grade 07Cr18Ni11Nb.

2. Manufacturing Processes Hot rolling

The billet is heated to 1150 - 1200℃, then punched and continuously rolled to form rough pipes, which are suitable for large-diameter thick-walled pipes.

Cold drawing

Through multiple cold drawing processes, the dimensional accuracy and surface finish are improved, and Φ10 - Φ108mm precision pipes are produced. Welding

Argon arc welding (TIG) or plasma welding (PAW) is used for thin-walled pipes, while submerged arc welding (SAW) is used for thick-walled pipes. After welding, 100% radiographic testing (RT) is required. 

VI. Market Trends and Supply

Capacity Layout

Enterprises such as China Iron and Steel and Baosteel have achieved large-scale production of 347H stainless steel pipes. In 2023, the market share of 347H products for solar thermal applications at China Iron and Steel reached over 35%.

Price Trends

The price of Φ51×8mm 347H seamless pipes in 2024 is approximately 28,000 - 32,000 yuan per ton, which is 10 - 15% higher than that of 321H, but lower than that of nickel-based alloys (such as Inconel 625), which is one-third of the latter.

Export Situation

Chinese 347H steel pipes are mainly exported to regions such as India and Southeast Asia for power station construction. The export volume increased by 12% in 2024. 

VII. Usage Notes

Environmental Restrictions

Avoid long-term use in an oxidizing atmosphere above 850℃ to prevent the formation of a loose oxide layer.

Stress Control

Stress relief treatment (such as re-heating at 650-700℃) is required at high temperatures to prevent stress corrosion cracking. Surface treatment

Pickling or mechanical polishing can enhance corrosion resistance, while passivation treatment (using HNO₃/HF solution) can improve the resistance to pitting corrosion. 

The 347H stainless steel pipe, due to its balance of high-temperature strength, corrosion resistance and processing performance, has become an indispensable key material in modern industry. With the development of fields such as concentrated solar power and ultra-supercritical power plants, its market demand will continue to grow. At the same time, the optimization of manufacturing processes (such as the industrial chain synergy upgrade of Jiu'an Steel) will further enhance the product performance and cost-effectiveness.