Lap Joint Flange

Lap Joint Flanges offer a cost-effective and flexible solution for piping systems that require frequent maintenance. At Rayoung, we manufacture high-precision lap joint flanges designed to work seamlessly with stub ends, providing easy alignment and rapid assembly for your critical infrastructure.

What is a Lap Joint Flange?

A Lap Joint Flange is a specialized component used in a two-part assembly. It consists of a Stub End (which is butt-welded to the pipe) and the backing flange itself. Unlike other styles, a lap joint flange is not welded to the pipe. Instead, it slides over the pipe and sits behind the stub end.

In the industry, you may hear these referred to by several names:

• Loose Flange
• Backing Flange
• Stub End Flange
• Vanstone or Backing Ring

The flange bore features a curved radius to accommodate the flared base of the stub end. This “loose” design allows the flange to rotate freely, making bolt-hole alignment effortless during installation.

How to Weld Lap Joint Flange?

One of the most common misconceptions is that the flange itself is welded. In a lap joint setup, the flange is never welded.

The welding process follows these steps:

1. Slide the Flange On: Slide the Lap Joint Flange onto the pipe section before the final fitting is attached.
2. Align the Stub End: Position the Stub End at the end of the pipe.
3. Butt-Weld: Perform a butt-weld to join the Stub End to the pipe.
4. Secure the Joint: Once the weld is cooled and inspected, slide the flange forward to the stub end and bolt it to the matching flange.

Because the flange is not in contact with the fluid, you can often use a carbon steel flange even if the piping system is stainless steel, significantly reducing material costs.

Is a Lap Joint Flange Raised Face?

No. Standard Lap Joint Flanges have a Flat Face (FF).

Unlike a Slip-on or Weld Neck flange, the Lap Joint Flange does not provide the sealing surface itself. The “lap” portion of the Stub End acts as the sealing face. When the assembly is bolted together, the flange exerts pressure on the back of the stub end, which then compresses the gasket against the mating flange.

If your project requires a specific sealing surface, it is the Stub End that must be selected with the correct face finish (such as phonographic serrated finish).

What is a Lap Joint Flange Used For?

Lap Joint Flanges are the preferred choice for systems where space is tight or frequent disassembly is required. Key applications include:

• Frequent Maintenance: Ideal for systems that need regular cleaning, inspection, or part replacement.
• Easy Alignment: Perfect for large-diameter or heavy piping where aligning bolt holes is difficult. The rotating flange simplifies the process.
• Corrosive Systems: In stainless or alloy piping, you can use a high-grade stub end with a cheaper carbon steel backing flange to save costs without compromising safety.
• Low-Pressure Applications: Widely used in water treatment, chemical processing, and low-pressure industrial lines.

Technical Specifications

Available Materials

• Carbon Steel: ASTM A105, A350 LF2 (Low Temp)

• Stainless Steel: A182 F304/304L, F316/316L, F321

• Alloy Steel: ASTM A182 F1, F11, F22, F5, F9, F91

Why Source From Our Factory?

As a professional flange manufacturer, we provide:

• Precision Machining: Ensuring the bore radius perfectly matches your stub ends.
• Strict Quality Control: 100% dimensional inspection and material traceability (MTC 3.1).
• Fast Turnaround: Large stock of raw materials for standard sizes to meet urgent project deadlines.

Contact Us for a Competitive Quote

Looking for reliable Lap Joint Flanges for your next project? Our technical team is ready to provide specifications and pricing.

Email: info@hb-steel.com

Tel/WhatsApp: +86-18003119682