Introduction

In high-temperature industrial piping systems, material selection directly impacts equipment safety, service life, and maintenance costs. For power generation, petrochemicals, boilers, heat exchangers, and high-temperature pressure equipment, 347 and 347H stainless steel pipes are common high-temperature austenitic stainless steel materials.
Because both have similar chemical compositions and the same stabilizing element (Niobium), many customers easily confuse them when making a selection:
What is the difference between 347 and 347H?
Does 347H have better corrosion resistance than 347?
In what situations should you choose 347?
Why do boilers and high-temperature steam systems tend to use 347H?
In fact, the biggest difference between the two is not their corrosion resistance, but their high-temperature mechanical properties.
In short:
347 is a stabilized austenitic stainless steel, mainly used in corrosion-resistant and general high-temperature environments; 347H is a high-carbon version of 347, specifically designed for high-temperature long-term pressure conditions, improving creep resistance and endurance strength.

1. Overview of 347 Stainless Steel Pipe

a) 347 stainless steel belongs to niobium-stabilized austenitic stainless steel. It is based on 304 stainless steel with the addition of niobium (Nb). Niobium combines with carbon to form stable niobium carbide (NbC), which reduces the formation of chromium carbide from the combination of carbon and chromium during welding, thereby reducing the risk of intergranular corrosion.
b) Main features:
Good corrosion resistance
Excellent welding performance
Good high temperature stability
Strong resistance to intergranular corrosion

2. Overview of 347H Stainless Steel Pipe

a) 347H is the high-carbon version of 347. The biggest difference between the two is the carbon content.
b) Higher carbon content can improve the strengthening effect of austenitic structure, giving the material the following properties at high temperatures:
Higher tensile strength
Higher yield strength
Better creep resistance
Longer service life at high temperatures

3. Chemical Composition Difference

4. High Temperature Performance Difference

a) 347 is suitable for medium and high temperature environments, but its creep resistance is limited under long-term high temperature and pressure conditions.
b) The main advantages of 347H are better creep resistance and higher endurance strength. Under the same conditions, it can better resist this long-term deformation and has a longer service life.
c) 347 is suitable for applications with temperatures below 500℃ that require higher welding performance, such as chemical pipelines and heat exchangers.
d) 347H is mainly used in environments with a temperature range of 500℃~800℃ and long-term pressure, such as high-pressure steam systems and power plant equipment.

5. 347 vs 347H Stainless Steel Pipe Selection Table

Although 347 and 347H belong to the same stabilized austenitic stainless steel system, they are designed for different application environments.
The main advantages of 347 are good corrosion resistance, excellent weldability, and stable high-temperature performance.
Suitable for general industrial pipelines, chemical equipment and heat exchangers.
347H improves high-temperature strength, creep resistance, and endurance strength by increasing carbon content.
Therefore, it is more suitable for power plant boilers, superheaters, reheaters, high-temperature steam pipelines, and petrochemical high-temperature pressure systems.
If corrosion resistance and weldability are the primary concerns, 347 is usually sufficient; however, if the equipment needs to operate under high temperature and high pressure conditions for extended periods, 347H is a more reliable choice for stainless steel pipes.