Lap Joint Flanges – Types, Uses, Stub Ends, Classes & Selection Guide

Lap Joint Flanges are a versatile flange connection used with a separate Stub End. Unlike conventional flanges that are permanently welded directly to the pipe, a Lap Joint Flange slides over the stub end and is free to rotate around the pipe connection.

This design can simplify flange alignment during installation and is particularly useful where frequent dismantling, inspection or maintenance is required.

Vandan Alloys manufactures and supplies Lap Joint Flanges and Stub Ends in carbon steel, stainless steel, duplex, super duplex, nickel alloys and other materials according to customer requirements.

What is a Lap Joint Flange?

A Lap Joint Flange is a loose-type flange designed to work together with a compatible Stub End.

The stub end is welded to the pipe. The Lap Joint Flange is then positioned over the stub end.

Because the flange can rotate before bolting, bolt-hole alignment can be easier compared with fixed flange designs.

The flange and stub end must be compatible in dimensions, facing and application.

What is a Stub End?

A Stub End is a short pipe fitting that is butt-welded to the pipe.

The stub end provides the sealing face against the gasket and mating flange, while the Lap Joint Flange sits behind its raised collar.

The stub end is therefore an essential part of a Lap Joint Flange assembly.

Lap Joint Flange & Stub End Combination

A typical Lap Joint connection consists of:

Pipe + Stub End + Lap Joint Flange + Gasket + Bolting + Mating Flange

The stub end is welded to the pipe, while the Lap Joint Flange remains loose around the stub end.

This arrangement allows the flange to rotate for easier bolt-hole alignment.

How Does a Lap Joint Flange Work?

The stub end is first fitted and welded to the pipe.

The Lap Joint Flange is placed over the pipe before or during assembly as required by the fabrication procedure.

After the stub end is welded, the flange can rotate around the stub-end collar.

During final assembly, the flange is aligned with the mating flange and bolted together using the specified gasket and bolting system.

Types of Lap Joint Flanges

Lap Joint Flanges can be supplied in different configurations depending on the applicable standard.

Raised Face Lap Joint Flange

RF Lap Joint Flanges are commonly used with matching raised-face flange connections.

Flat Face Lap Joint Flange

FF Lap Joint Flanges are used where a flat-face connection is specified.

RTJ Lap Joint Flange

Where permitted by the applicable standard and configuration, RTJ Lap Joint Flanges may be supplied for ring-type joint applications.

The RTJ groove and mating ring dimensions must correspond to the applicable standard.

Lap Joint Flange Pressure Classes

Common ASME pressure classes include:

• Class 150

• Class 300

• Class 400

• Class 600

• Class 900

• Class 1500

• Class 2500

The available size and class combination depends on the applicable standard.

For EN applications, PN-rated configurations may also be required, including:

• PN10

• PN16

• PN25

• PN40

• PN63

• PN100

• PN160

The actual rating must be confirmed against the applicable standard and project specification.

Lap Joint Flange Size Range

Lap Joint Flanges are available across a broad range of nominal pipe sizes, subject to the applicable standard.

Typical requirements may include:

• Small diameter piping

• Medium diameter piping

• Large diameter piping

• Process piping

• Custom dimensions

For large-diameter or special requirements, customers can provide a drawing or project specification for review.

Lap Joint Flange Materials

Vandan Alloys supplies Lap Joint Flanges in various material groups.

Carbon Steel

Common grades include:

• ASTM A105

• ASTM A105N

Stainless Steel

Common grades include:

• ASTM A182 F304

• ASTM A182 F304L

• ASTM A182 F316

• ASTM A182 F316L

• F321

• F347

• F310

• F904L

Duplex Stainless Steel

• Duplex 2205

• UNS S31803

• UNS S32205

Super Duplex Stainless Steel

• Super Duplex 2507

• UNS S32750

• UNS S32760

Nickel & Special Alloys

Depending on the requirement, Lap Joint Flanges and Stub Ends may be supplied in selected:

• Monel

• Inconel

• Incoloy

• Hastelloy

• Titanium

• Other special alloys

Material selection should be based on service conditions and the applicable material specification.

A105N Lap Joint Flanges

ASTM A105N Lap Joint Flanges are normalized carbon steel forged flanges supplied according to the applicable material specification.

If the normalized condition is required, A105N should be clearly stated in the purchase specification.

A typical requirement can be specified as:

ASTM A105N + Lap Joint Flange + Size + Class + Facing + Quantity

The material requirement for the Stub End should also be clearly specified because the stub end is the component directly welded to the pipe.

Stainless Steel Lap Joint Flanges

Stainless Steel Lap Joint Flanges are widely considered for applications where corrosion resistance and material compatibility are important.

Common grades include:

304 / 304L

316 / 316L

321

347

310 / 310S

904L

The flange and stub-end material combination should be selected according to the piping specification and service conditions.

Duplex & Super Duplex Lap Joint Flanges

Duplex 2205 and Super Duplex 2507 can be supplied for applications requiring specific corrosion resistance and mechanical performance.

Common grades include:

UNS S31803 / S32205

UNS S32750 / S32760

The required grade should be clearly specified for both the flange and stub end where applicable.

Stub End Types

Stub Ends are available in different dimensional configurations according to the applicable standard.

Common configurations include:

Type A Stub End

The stub end is designed for use with a Lap Joint Flange and has the required flange-facing profile.

Type B Stub End

Type B configurations may be used with suitable flange arrangements according to the applicable specification.

Type C Stub End

Special stub-end configurations may be available according to the applicable dimensional and fabrication requirements.

The exact stub-end type, dimensions and compatibility should be confirmed against the governing standard.

Stub End Material Selection

Stub Ends can be supplied in materials such as:

• Carbon Steel

• Stainless Steel

• Duplex

• Super Duplex

• Alloy Steel

• Nickel Alloys

• Other special materials

For corrosive services, the stub end material is especially important because it is directly exposed to the piping medium.

Advantages of Lap Joint Flanges

Easy Bolt-Hole Alignment

The loose flange design allows rotation around the stub end, which can simplify alignment.

Useful for Frequent Dismantling

Lap Joint connections can be convenient where piping needs to be regularly opened for inspection or maintenance.

Reduced Flange Replacement Cost in Some Applications

Because the flange is not permanently welded to the pipe, it may be possible to reuse or replace the loose flange separately, subject to condition and specification.

Suitable for Corrosion-Resistant Stub Ends

A corrosion-resistant stub end can be combined with a suitable backing flange where permitted by the engineering design.

Lap Joint Flange Applications

Lap Joint Flanges may be considered for:

• Chemical processing

• Petrochemical plants

• Oil & Gas

• Refineries

• Water treatment

• Process piping

• Marine applications

• Food and pharmaceutical systems

• Industrial piping

• Maintenance piping

• Systems requiring frequent dismantling

Selection should always be based on the applicable piping code and project requirements.

Lap Joint Flange vs Slip-On Flange

Lap Joint Flange:
Works with a separate Stub End and remains loose around the stub-end collar.

Slip-On Flange:
Slides over the pipe and is attached to the pipe by welding.

The Lap Joint arrangement offers flange rotation and can be useful for alignment and maintenance applications.

Lap Joint Flange vs Weld Neck Flange

Lap Joint Flange:
Uses a separate stub end and loose backing flange.

Weld Neck Flange:
Has an integral tapered hub and is connected directly to the pipe by butt welding.

The appropriate design depends on service conditions, piping loads, fabrication requirements and applicable standards.

Lap Joint Flange Installation

Before assembly, verify:

• Flange size

• Pressure class

• Material

• Stub-end type

• Stub-end dimensions

• Facing

• Pipe OD

• Gasket

• Bolt size and material

• Bolt-hole alignment

The stub end should be properly welded to the pipe according to the applicable welding procedure.

The Lap Joint Flange should be positioned correctly behind the stub-end collar.

During final assembly, the flange should be aligned with the mating flange without forcing the piping into position.

Gasket Selection

The gasket should be compatible with:

• Flange facing

• Stub-end face

• Process medium

• Operating temperature

• Operating pressure

• Material compatibility

For RTJ configurations, the ring and groove dimensions must correspond to the applicable standard.

Lap Joint Flange Inspection

Inspection requirements may include:

• Visual inspection

• Dimensional inspection

• Flange OD and thickness

• Bore inspection

• PCD and bolt-hole inspection

• Facing inspection

• Stub-end dimensions

• Material identification

• Chemical analysis

• Mechanical testing

• Heat treatment verification where applicable

• Marking and traceability

• Third-party inspection

Inspection requirements should be confirmed before production.

MTC & Documentation

For applicable orders, EN 10204 Type 3.1 Material Test Certificate can be supplied.

Documentation may include:

• Material grade

• Heat number

• Chemical composition

• Mechanical properties

• Heat treatment information where applicable

• Dimensional inspection

• Traceability records

Additional inspection documentation can be arranged according to the project specification.

Custom Lap Joint Flanges

Vandan Alloys can evaluate custom Lap Joint Flanges and Stub Ends according to customer drawings or technical requirements.

Custom requirements may include:

• Special flange dimensions

• Special stub-end dimensions

• Customized bore

• Special PCD

• Special bolt-hole pattern

• Special facing

• Special thickness

• Special material

• Non-standard configurations

Customers can provide PDF drawings, CAD drawings, dimensional sketches or project specifications for review.

How to Order Lap Joint Flanges

For quotation, provide:

Flange Size / NPS:
Pressure Class / PN:
Flange Material:
Stub End Material:
Stub End Type:
Facing: RF / FF / RTJ
Pipe OD / Wall Thickness:
Standard:
Quantity:
Inspection Requirement:
Delivery Location:

For special requirements, provide the flange and stub-end drawing.

Vandan Alloys – Lap Joint Flange & Stub End Manufacturer

Vandan Alloys manufactures and supplies Lap Joint Flanges and Stub Ends for industrial piping, process plants, engineering projects, maintenance applications and international export requirements.

Our supply range includes:

• Carbon Steel Lap Joint Flanges

• A105 Lap Joint Flanges

• A105N Lap Joint Flanges

• Stainless Steel Lap Joint Flanges

• Duplex Lap Joint Flanges

• Super Duplex Lap Joint Flanges

• Alloy Steel Lap Joint Flanges

• Nickel Alloy Lap Joint Flanges

• Stainless Steel Stub Ends

• Carbon Steel Stub Ends

• Duplex Stub Ends

• Super Duplex Stub Ends

• Custom Stub Ends and Lap Joint Flanges

We support requirements for different sizes, pressure classes, materials, standards, facing configurations and custom dimensions, subject to the applicable specification.

If you are looking for a Lap Joint Flange Manufacturer in India, A105N Lap Joint Flange Supplier, Stainless Steel Lap Joint Flange Manufacturer, Stub End Manufacturer, ASME Lap Joint Flange Supplier or Custom Lap Joint Flange Exporter, send your complete requirement to Vandan Alloys.

Send your Lap Joint Flange or Stub End enquiry, drawing or specification for quotation.

Vandan Alloys 

Manufacturer of All Types of Flanges

3/5, Sakar Bhavan, Ground Floor, 6th  Khetwadi lane, SVP Road ,Mumbai – 400 004. India

TEL+91 022 6610 9925Mobile no: 09892882255  GSTIN:  27AUMPS2067F1ZB

Email: info@vandanalloys.com ; Web: www.vandanalloys.com

Please visit Our Flanges Division:www.vandanalloys.net

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Vandan Alloys manufactures and exports Lap Joint Flanges and Stub Ends in A105, A105N, stainless steel, duplex and nickel alloys. ASME, EN and custom sizes.

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