Stainless Steel 304L Pipe Fittings

The differences between 304/304L/304H stainless steel pipe fittings primarily involve their carbon content and the resulting effects on their properties and applications. Here’s a detailed comparison:
1. Carbon Content
SAE 304 stainless steel: Contains a carbon content of up to 0.08%.
Stainless steel – AISI 304l : Has a lower carbon content, with a maximum of 0.03%.
Grade 304H stainless steel: Has a higher carbon content, with a range of 0.04% to 0.10%.
2. Mechanical Properties and Applications
SAE 304 stainless steel:
Uses: Widely used in a variety of applications due to its good corrosion resistance, formability, and weldability. Common in kitchen equipment, storage tanks, and piping systems.
Properties: Balanced combination of strength, corrosion resistance, and workability. Suitable for applications where these factors are required in moderate conditions.
304L Stainless Steel:
Uses: Ideal for welding applications where the risk of intergranular corrosion is high due to welding. Common in chemical processing equipment, heat exchangers, and marine environments.
Properties: Lower carbon content minimizes carbide precipitation during welding, which enhances corrosion resistance. Slightly lower tensile strength compared to 304 but better resistance to corrosion after welding.
304H Stainless Steel:
Uses: Suitable for high-temperature applications due to its higher carbon content which provides increased strength at elevated temperatures. Common in pressure vessels, boiler components, and heat exchangers operating above 500°C (932°F).
Properties: Higher carbon content increases tensile and yield strength at elevated temperatures. Provides better creep resistance but may be more susceptible to sensitization (carbide precipitation) which can lead to intergranular corrosion if exposed to certain environments without proper heat treatment.
3. Corrosion Resistance
304 and 304L: Both have excellent corrosion resistance in a wide range of environments, including food processing and chemical industries. The lower carbon content of 304L enhances its resistance to intergranular corrosion after welding.
Grade 304H stainless steel: While it has similar corrosion resistance to 304 in many environments, its higher carbon content can make it more susceptible to intergranular corrosion if not properly heat-treated.
4. Standards and Codes
SAE 304 stainless steel: Often meets specifications such as ASTM A403 (for pipe fittings) and ASME SA403.
Stainless steel – AISI 304l: Typically specified under the same standards but with designations indicating its lower carbon content (e.g., ASTM A403/A403M-17).
304H: Specified under standards that emphasize high-temperature applications, such as ASTM A403 with special notation for its high carbon content.

The choice between 304, 304L, and 304H stainless steel pipe fittings depends on the specific requirements of the application, particularly concerning temperature, welding conditions, and corrosion resistance.
SAE 304 stainless steel: General use with balanced properties.
Stainless steel – AISI 304l: Best for welding and higher resistance to intergranular corrosion.
Grade 304H stainless steel: Suitable for high-temperature and high-strength applications.