Lap Joint Flange Manufacturer, Supplier & Exporter
A lap joint flange (LJF) is a loose backing flange that slides over a stub end welded to the pipe. It is never welded itself: the flange bears against the lap of the stub end and can rotate freely around the pipe. Raaj Fittings manufactures and exports lap joint flanges to ASME B16.5 in carbon steel, stainless steel, alloy steel, duplex and nickel alloys.
Because only the stub end touches the process fluid, a lap joint lets you pair an expensive corrosion-resistant stub end with a lower-cost carbon steel flange. The free-turning flange also makes bolt-hole alignment simple, which is valuable on lines that are taken apart regularly for cleaning or inspection.
Lap joint flanges are supplied with EN 10204 3.1 mill test certificates, with 3.2 certification and third-party inspection on request. Matching stub ends are available from our buttweld fittings range.
We export lap joint flanges to EPC contractors, refineries and stockists across the Middle East and GCC, Europe and the Americas, made to the ASME, EN or DIN standard your project specifies, with PED-compliant supply for European projects on request.
Lap Joint Flange Specifications
½" NPS to 24" NPS to ASME B16.5
ASME Class 150, 300, 600, 900, 1500 and 2500
ASME B16.5; EN 1092-1 Type 02 / Type 04 (loose flanges) and other standards on request
Machined to clear the stub end, with a radiused corner on the face side to suit the stub end lap
Flat contact face against the stub end; sealing is on the stub end lap
Stub ends to ASME B16.9 (long pattern) or MSS SP-43 (short pattern)
Forged or cut from plate and CNC machined
EN 10204 3.1 mill test certificate as standard; EN 10204 3.2 on request
Materials & Grades
We supply lap joint flanges in the following materials and grades. All grades are supplied with EN 10204 3.1 / 3.2 Mill Test Certificates.
Stainless Steel Lap Joint Flanges
Stainless steel flanges offer excellent corrosion resistance and are essential in chemical, pharmaceutical, food processing, and marine environments.
(ASTM A182 F304 / F304L) General corrosion resistance
(ASTM A182 F316 / F316L) Superior resistance to chlorides, acids; marine & pharmaceutical service
(ASTM A182 F316H) High-temperature elevated creep strength
(ASTM A182 F321) Titanium-stabilized; suitable for sustained elevated temperatures
(ASTM A182 F347) Columbium-stabilized; used in heat exchangers and high-temperature piping
High alloy; exceptional resistance to strong acids
Duplex & Super Duplex Stainless Steel Lap Joint Flanges
Duplex and super duplex grades offer approximately twice the yield strength of standard austenitic stainless steel, combined with excellent resistance to stress corrosion cracking and pitting — making them ideal for offshore, subsea, and chemical processing.
(UNS S31803 / S32205) Used in offshore platforms and chemical processing plants
(UNS S32750) Ideal for seawater handling and desalination systems
(UNS S32760) Designed for high-chloride offshore service applications
Nickel Alloy Lap Joint Flanges
For the most aggressive corrosive environments — including concentrated acids, caustic solutions, sour gas service, and extreme temperatures — we offer flanges in a full range of nickel alloys.
(UNS N06600) High-temperature oxidation resistance
(UNS N06625) Outstanding corrosion resistance for offshore and subsea service
(UNS N08825) Excellent resistance to phosphoric and sulfuric acids
(UNS N10276) Broad-spectrum corrosion resistance in acids and chlorides
(UNS N06022) Superior resistance to oxidizing acids
(UNS N04400) Suitable for seawater, hydrofluoric acid, and marine environments
(UNS N08020) Engineered for sulfuric acid service
Exceptional corrosion resistance with low weight
(C70600 / C71500) Preferred for marine and seawater piping systems
Carbon Steel Lap Joint Flanges
Carbon steel is the standard choice for general-purpose, non-corrosive, and elevated-temperature services. The primary grade for forged carbon steel flanges is ASTM A105, and for low-temperature service, ASTM A350 LF2.
Primary grade for forged carbon steel fittings and flanges — covers ambient and elevated-temperature service in pressurised piping systems.
Low-temperature carbon steel, impact-tested for service down to -46°C (-50°F) — LNG, cold climate, and cryogenic piping applications.
Alloy Steel Lap Joint Flanges
Alloy steel flanges are specified for high-temperature, high-pressure service in power generation, petrochemical, and refinery applications.
(5% Cr, ½% Mo) Designed for elevated temperature refinery service
(9% Cr, 1% Mo) Suitable for high-temperature steam and hydrogen service
(1¼% Cr, ½% Mo) Widely used in thermal power plant piping systems
(2¼% Cr, 1% Mo) Used in high-temperature pressure vessels and reactors
(9% Cr, 1% Mo, V, Nb) Engineered for ultra-high-temperature power plant steam lines
How a Lap Joint Works
A stub end — a short length of pipe with a flared lip — is butt-welded to the pipe. The lap joint flange slides over the pipe before welding and is then pulled up against the back of the lip by the bolts. The gasket seals between the faces of the two stub ends, so the flange itself is never wetted by the process fluid.
- Cost saving — a carbon steel backing flange can be used with stainless steel, duplex or nickel alloy piping.
- Easy alignment — the flange rotates freely, so bolt holes line up without twisting the pipe.
- Quick dismantling — ideal for lines opened often for cleaning or inspection.
- Reusable flanges — backing flanges can be recovered when piping is replaced.
Long and Short Pattern Stub Ends
ASME B16.9 stub ends (long pattern) are commonly used with ASME B16.5 lap joint flanges in process piping. MSS SP-43 stub ends (short pattern) are lighter and used mainly on light-wall stainless steel piping. Check that the stub end lap diameter and the flange bore radius match the same standard.
Limitations
Because the flange is loose, the joint carries bending loads less well than a weld neck flange. Lap joints are best for low- to moderate-pressure lines and where routine dismantling, alignment or material cost are the main concerns. For a fixed, welded alternative on low-pressure lines, see the slip on flange.
Applications & Industries
- Stainless steel, duplex and nickel alloy process piping with carbon steel backing flanges
- Chemical, pharmaceutical and food plants where lines are dismantled for cleaning
- Water treatment and desalination plants
- Pulp and paper and fertiliser plants
- Lined and coated piping systems
- Large-diameter piping where bolt-hole alignment is difficult
See all flange types and our range of buttweld fittings, including stub ends.
Testing, Inspection, Marking & Packing
Lap joint flanges are produced under our quality assurance process:
- Incoming material verification with PMI testing
- Chemical and mechanical testing to the applicable ASTM material specification
- Dimensional inspection of bore, corner radius, thickness, bolt circle and bolt holes
- Marking with grade, size, class, standard and heat number
Supplied with EN 10204 3.1 mill test certificates; EN 10204 3.2 certificates and third-party inspection are available on request.
Flanges are packed for export with gasket faces protected by covers, rust-preventive coating on carbon and alloy steel, and seaworthy wooden cases; marking, tagging and packing to your specification are available on request.
Why Choose Raaj Fittings for Lap Joint Flanges?
Raaj Sagar Steels has supplied piping components since 2003 and today manufactures flanges at two plants in India for buyers in the Middle East, Europe and the Americas.
- Manufactured in-house — Lap joint flanges are made in our own plants, so material, dimensions and delivery stay under our control.
- Ready stock, short lead times — common sizes and grades are held in stock for prompt dispatch; other sizes, grades and specials are manufactured to order.
- Certified quality — ISO 9001:2015, ISO 14001:2015 and ISO 45001:2018 certified; PED 2014/68/EU and IBR supply available, and NACE MR0175 / ISO 15156 material on request.
- 100% material verification — PMI testing on incoming material and EN 10204 3.1 mill test certificates with every order; 3.2 certificates on request.
- Third-party inspection ready — we regularly work with SGS, Bureau Veritas, TÜV and DNV.
- Export documentation — MTCs, certificates of origin, packing lists and inspection reports to suit projects in the GCC, Europe and the Americas.
- Export packing — seaworthy packing with end and face protection, and packing to your specification on request.
- Fast response — our team replies to enquiries within one business day.
Lap Joint Flanges — FAQs
A lap joint flange is a loose backing flange used with a stub end. The stub end is welded to the pipe and the flange slides over it, bearing against the back of the stub end lip when the bolts are tightened.
Because the flange does not contact the process fluid, a low-cost carbon steel flange can be used with stainless or alloy piping. The flange also rotates freely, which makes bolt-hole alignment and dismantling easy.
No. The flange has a flat contact face that bears on the stub end. The gasket seals between the laps of the two stub ends, not against the flange.
ASME B16.9 long-pattern stub ends are standard for process piping with ASME B16.5 lap joint flanges. MSS SP-43 short-pattern stub ends are used mainly on light-wall stainless steel lines.
They are available up to Class 2500, but because the flange is loose the joint is less able to resist bending loads than a weld neck joint. They are mostly used at low to moderate pressures.
Yes. We supply lap joint flanges for projects under the European Pressure Equipment Directive (PED 2014/68/EU), and with IBR certification for Indian boiler applications. NACE MR0175 / ISO 15156 compliant material is also available on request for sour service in the Middle East and the Americas.
