Differences in Material Selection for Various Types of Flanges

The selection of materials for different types of flanges is influenced by the structural characteristics, operating conditions, and performance requirements of the flange and the piping system. Below is a detailed breakdown of material selection for common flange types:

1. Plate Flanges

Structural Characteristics: Plate flanges are simple, typically consisting of a flat disc with bolt holes and a sealing surface, welded or threaded directly to the pipe end.
Application: These flanges are commonly used in low-pressure, room-temperature systems, such as water supply, drainage, HVAC, and non-critical applications.
Material Selection:

• Carbon Steel: Suitable for general low-pressure, room-temperature applications. Carbon steel materials like Q235B offer a balance between cost-effectiveness and strength.
• Stainless Steel: When corrosion resistance is needed, particularly in applications such as food and beverage pipelines, or mildly corrosive chemical media, materials like 304 stainless steel are used, offering good resistance to oxidation, acids, and alkalis.

2. Butt-Welding Flanges

Structural Characteristics: Butt-welding flanges have a longer neck and are welded to the pipe end, resulting in high-quality, durable connections. These flanges can withstand higher pressures and temperatures due to the strong welded joint.
Application: Typically used in high-pressure, high-temperature, or hazardous media pipelines such as those found in petrochemical, electric power, and natural gas industries.
Material Selection:

• Carbon Steel: For systems with moderate temperature and pressure, materials like No. 20 carbon steel are suitable. These provide good weldability, strength, and pressure resistance.
• Alloy Steel: In high-temperature and high-pressure environments, chromium and molybdenum alloy steels such as 15CrMo, 12Cr1MoV, or similar grades are commonly used. These materials offer superior high-temperature strength, oxidation resistance, and creep resistance.
• Stainless Steel: For highly corrosive environments or systems that require high cleanliness, stainless steels like 316L are preferred, owing to their excellent corrosion resistance, particularly against intergranular corrosion.

3. Socket Welding Flanges

Structural Characteristics: Socket welding flanges feature a socket into which the pipe is inserted before welding, offering easier installation and better sealing performance.
Application: Primarily used in small-diameter pipelines in industries such as chemicals, oil refining, and others, especially where sealing integrity is critical.
Material Selection:

• Carbon Steel: For small-diameter, low-pressure pipelines with non-corrosive media, carbon steel (e.g., Q235B) provides an economical choice.
• Stainless Steel: In cases where corrosion resistance is essential, particularly for pipelines conveying corrosive substances like acids or alkalis, materials such as 304 or 316L stainless steel are preferred for their excellent resistance to corrosive environments.

4. Loose Set Flanges

Structural Characteristics: Loose set flanges consist of a loose sleeve ring and a flange, with the sleeve ring fitted around the pipe and the flange bolted to it. This design allows relative movement between the pipe and the sleeve ring, making it ideal for systems with thermal expansion or frequent disassembly.
Application: Used in piping systems that experience axial displacement, vibration, or need to be frequently disassembled, such as pump and compressor inlet/outlet lines.
Material Selection:

• Carbon Steel/Stainless Steel: The sleeve ring is typically made from the same material as the pipe (e.g., carbon steel or stainless steel). The flange material can vary depending on corrosion resistance requirements; for general conditions, carbon steel is used, while stainless steel is selected for more corrosive environments.
• Non-Ferrous Metals: For specialized applications requiring enhanced corrosion resistance or other unique properties, non-ferrous materials like copper alloys or nickel alloys may be used to meet specific performance demands.

5. Threaded Flanges

Structural Characteristics: Threaded flanges are connected to the pipe using internal threads, allowing for easy installation and disassembly without welding.
Application: Ideal for situations where welding is not feasible, such as in field installations with limited access or for systems requiring frequent disassembly. They are typically used for low-pressure, non-corrosive applications.
Material Selection:

• Carbon Steel: For low-pressure, non-corrosive media, carbon steel materials like Q235B are commonly used, providing an economical and reliable solution.
• Stainless Steel: When the conveyed medium is corrosive or when higher cleanliness is required, stainless steel grades like 304 are used, offering resistance to corrosion and oxidation.

Conclusion

Material selection for flanges depends on factors such as pressure, temperature, corrosion resistance, and application-specific requirements. Carbon steel is commonly used in low-pressure, non-corrosive environments, while stainless steel and alloy steels are preferred for corrosive, high-pressure, and high-temperature systems. Non-ferrous materials like copper and nickel alloys may be selected for specialized applications where enhanced corrosion resistance or other unique properties are needed.