Weld Neck Flange

A Weld neck flange is a type of flange designed to be welded onto the end of a pipe. It’s distinguished by its long neck, which is beveled to match the bevel on the pipe. The purpose of the neck is to transfer stress from the flange to the pipe, reducing the concentration of stress at the base of the flange. This design helps to prevent cracking and leaking, making weld neck flanges particularly suitable for high-pressure and high-temperature applications.

Weld neck flanges typically have a raised face, which provides a sealing surface when bolted to a mating flange or fitting. They are commonly used in industries such as oil and gas, petrochemical, power generation, and process piping systems where reliable sealing under extreme conditions is essential.

Material Grades

Stainless Steel: ASTM / ASME SA403 GR WP “S” / “W” / “WX” 304, 304L, 304H, 309, 310H, 316L, 316H, 317, 317L, 321, 321H, 904, 904L, 347, 347H.

Duplex Steel: ASTM / ASME SA815 UNS NO. S31803, S32205, S32550, S32750, S32760.

Carbon Steel: ASTM / ASME A234 WPB, WPC, ASTM / ASME A860 WHY42, WHY46, WHY52, WH60, WPHY65 & WPHY70

Alloy Steel : ASTM / ASME A234 WP1, WP5, WP9, WP11, WP 12, WP22, WP23, WP91

Sizes

Weld neck flanges are available in a wide range of sizes to accommodate various piping requirements:

• Nominal Pipe Size (NPS): Ranges from ½ inch to 60 inches (and beyond for custom applications).
• Diameter: The outside diameter (OD) of flanges increases with the NPS.
• Thickness: The thickness and dimensions of the weld neck flanges vary depending on the pressure class.

Pressure Ratings

Pressure ratings for weld neck flanges are categorized into different classes, indicating the maximum pressure they can withstand at a given temperature. The most common pressure classes are:

• Class 150 (PN 20)
• Class 300 (PN 50)
• Class 400 (PN 64)
• Class 600 (PN 100)
• Class 900 (PN 150)
• Class 1500 (PN 250)
• Class 2500 (PN 420)

Higher pressure classes indicate the flange can withstand greater pressures. Each class has specific dimensional standards ensuring compatibility and safety in their respective applications.

Conclusion

When selecting a weld neck flange, it is crucial to consider the standard, grade, size, and pressure rating appropriate for the specific application. Consulting the relevant ASME/ANSI, MSS, API, or ISO standards will provide the detailed specifications needed to ensure the proper selection and use of weld neck flanges in your piping system.