Lap Joint Flange

A Lap Joint Flange is a type of pipe flange comprising two parts: a flat, circular disc (the “stub end”) and a ring or hub (the “lap joint”). The stub end is typically welded to the pipe or fitting, while the lap joint rotates freely around it. This design facilitates easy alignment during assembly.

These flanges are commonly used in piping systems where frequent dismantling and reassembly are necessary, such as those handling corrosive or abrasive fluids or in systems with thermal expansion considerations. They offer versatility, allowing for adjustments and disassembly without disturbing the entire piping system.

Lap joint flanges come in various materials, sizes, and facings to suit different applications and operating conditions. They are available with flat face (FF), raised face (RF), or ring type joint (RTJ) facings, depending on sealing requirements.

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

Lap joint flanges are available in a range of sizes to accommodate different piping requirements:

• Nominal Pipe Size (NPS): Typically ranges from ½ inch to 24 inches. Larger sizes can be custom made if required.
• Diameter and Thickness: The outside diameter (OD) and thickness of the flange vary according to the pressure class and nominal size. The dimensions of the lap joint flange are generally similar to those of the slip-on flange, but they lack the hub.

Pressure Ratings

Pressure ratings for lap joint flanges indicate the maximum pressure they can withstand at a given temperature. The common pressure classes include:

• 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)

Conclusion

When selecting a lap joint flange, it’s important to consider the nominal pipe size, pressure class, and the specific application requirements. Adherence to standards such as ASME/ANSI B16.5 ensures compatibility and safety. Lap joint flanges offer the benefits of easy alignment and cost efficiency, making them suitable for systems requiring frequent maintenance and assembly.