Lap Joint Flange for Flexible and Cost-Effective Piping Connections

A lap joint flange, also known as a loose flange or LJ flange, is a two-piece flange assembly consisting of a stub end and a loose backing flange. Unlike conventional welded flanges, the flange itself is not welded directly to the pipe. Instead, the stub end is welded to the pipe, while the lap joint flange rotates freely around the stub end for easier alignment and installation.

DTC manufactures and supplies carbon steel lap joint flanges, stainless steel lap joint flanges, and alloy steel lap joint flanges according to international standards including ASME B16.5, EN 1092-1, and JIS B2220.

Lap joint flanges are especially suitable for piping systems requiring frequent maintenance, alignment flexibility, or corrosion-resistant materials where reducing material costs is important.

Key Features of Lap Joint Flange

Easy Alignment During Installation

The loose flange design allows the flange to rotate freely around the stub end, making bolt-hole alignment easier during installation.

Suitable for Frequent Maintenance

The detachable design allows easier disassembly and reassembly compared with welded flange connections.

Cost Saving for Corrosive Applications

Only the stub end contacts the process fluid, allowing expensive corrosion-resistant materials to be reduced to the wetted area.

Wide Material Compatibility

Available in carbon steel backing flanges combined with stainless steel stub ends for cost-effective corrosion resistance.

Technical Specifications

Common Materials

Carbon Steel Lap Joint Flange

Typical materials:

• ASTM A105
• ASTM A350 LF2
• Q235B / Q355

Applications:

• Water pipelines
• Fire protection systems
• General industrial piping

Stainless Steel Lap Joint Flange

Typical materials:

• ASTM A182 F304
• ASTM A182 F316
• 304L / 316L

Applications:

• Chemical processing
• Food processing
• Pharmaceutical systems
• Corrosive media pipelines

Lap Joint Flange Components

A complete lap joint flange connection includes:

1. Stub End

The stub end is welded directly to the pipe and provides the sealing surface.

Common types:

• Type A Stub End
• Type B Stub End
• Type C Stub End

2. Loose Backing Flange

The backing flange provides bolt connection but does not contact the fluid.

Common materials:

• Carbon steel
• Stainless steel
• Alloy steel

Lap Joint Flange Applications

Lap joint flanges are widely used in:

• Chemical Processing Plants
• Oil & Gas Industry
• Petrochemical Systems
• Food & Beverage Industry
• Water Treatment
• Marine Engineering
• Pharmaceutical Equipment
• Large Diameter Piping Systems

Lap Joint Flange vs Slip-On Flange

Lap Joint Flange vs Weld Neck Flange

Why Choose DTC Lap Joint Flanges?

Reliable Manufacturing Supply

DTC works with experienced flange manufacturers to provide stable quality and competitive pricing.

Complete Specification Options

Available in:

• Different pressure classes
• Various materials
• Customized dimensions
• Special drilling patterns

OEM & Private Label Support

DTC supports:

• Customer logo marking
• Customized packaging
• Special coating requirements
• Project-based specifications

Quality Documentation

Available documents include:

• EN10204 3.1 Material Test Certificate
• Dimensional Inspection Report
• Chemical Composition Report
• Mechanical Test Report

Frequently Asked Questions (FAQ)

What is a lap joint flange?

A lap joint flange is a loose flange used together with a stub end. The flange rotates around the stub end, allowing easier alignment and installation.

What is another name for a lap joint flange?

Lap joint flange is also called a loose flange or LJ flange.

What is the difference between lap joint flange and slip-on flange?

A slip-on flange is welded directly to the pipe, while a lap joint flange uses a separate stub end and loose backing flange.

Can lap joint flanges be used with stainless steel pipes?

Yes. Lap joint flanges are commonly used with stainless steel stub ends to reduce material costs in corrosive applications.