Lapped Joint Flanges Manufacturer & Exporter — India
ASME B16.5 | Class 150 – 2500 |
LJ Flange + Stub End System |
360° Rotating Ring | ISO 9001:2015
✓ ASME B16.5
✓ Class 150 – 2500
✓ LJF + Stub End
✓ ½″ – 56″ NB
✓ 360° Rotating Ring
✓ Mixed Material Options
✓ Lined Pipe Compatible
✓ EN 10204 3.1/3.2 MTC
✓ ISO 9001:2015
A lapped joint flange (LJF), also called a loose flange or backing flange, is a two-piece flanging system consisting of a loose rotating flange ring and a lap joint stub end. The stub end is butt-welded to the pipe; the flange ring slides freely over the pipe and backs up against the stub end's lapped face. Because the ring can rotate freely through 360°, bolt holes align with the mating flange without rotating the pipe — a critical advantage when connecting to fixed equipment or in tight spaces.
Tesco Steel & Engineering, ISO 9001:2015 certified, manufactures and exports lapped joint flanges from ½″ NB to 56″ NB in all ASME B16.5 pressure classes (150 through 2500) across the full range of materials. A key economic benefit of the LJF system: only the stub end contacts the process fluid, so the stub end can be made from the required corrosion-resistant alloy (e.g., SS 316L, Hastelloy C276, Titanium) while the flange ring is supplied in low-cost carbon steel — reducing assembly cost by up to 60% versus an all-alloy weld neck flange of the same size.
At a glance: a lapped joint = two parts — a plain backing flange ring that never touches the fluid, spinning freely over a butt-welded stub end whose lap face does the sealing. Result: bolt holes align themselves, and the expensive alloy is only in the stub end while the ring can be plain carbon steel. Specify it by size, class, stub-end standard (MSS SP-43 Type A/B), ring material and stub-end material.
Key Advantages of Lapped Joint Flanges
▶ 360° Bolt Hole Alignment
The loose flange ring rotates freely around the stub end, enabling bolt holes to be aligned with the mating flange without rotating or stressing the pipe — essential when connecting to fixed nozzles, pumps, or tanks.
▶ Easy Dismantling & Re-assembly
The flange ring is not welded to the pipe. The joint can be broken and re-made repeatedly without disturbing pipe welds — ideal for systems requiring frequent inspection, cleaning, or maintenance access.
▶ Material Cost Savings
Only the stub end contacts the fluid. Use an alloy stub end (SS 316L, Hastelloy, Titanium) with a low-cost ASTM A105 carbon steel flange ring — reducing flanging cost by 40–60% versus all-alloy weld necks on corrosive services.
▶ Lined & Clad Pipe Compatible
The stub end face can accommodate PTFE liners, rubber linings, or glass linings that extend over the sealing face — making LJFs the standard choice for non-metallic lined piping systems where a raised face weld neck is not compatible.
▶ Cryogenic & Low-Temperature Service
LTCS and SS 304L/316L stub ends with carbon steel flange rings are widely used in LNG, cryogenic storage, and cold process service — where alloy material continuity at the sealing face is required but the flange backing ring does not need to be alloy-grade.
▶ Wide Standard & Material Range
ASME B16.5 Class 150–2500, ½″–56″ NB, in carbon steel, SS 304/316/316L, duplex 2205/2507, Inconel 625, Hastelloy C276, Titanium Gr.2, Monel, and Copper Nickel — all with full EN 10204 3.1/3.2 MTC documentation.
How Our Lapped Joint Flanges Are Manufactured
1
Forging — the backing ring is forged from certified heats (often economical carbon steel, since it never contacts the fluid), and matching stub ends are made from the process-wetted alloy per MSS SP-43 or ASME B16.9.
2
Heat treatment — normalizing for carbon steel rings, solution annealing for stainless and nickel stub ends, with the thermal record retained per heat.
3
Machining — the ring's bore and the critical back-face radius are machined to seat the stub-end lap without stress concentration; bolt holes to ASME B16.5.
4
Lap facing — the stub end's lap face receives the gasket finish; the ring needs no facing at all — it only pushes.
5
Testing & marking — mechanical and chemical verification against each heat, PMI where specified, then permanent marking of grade, size, class and heat number on ring and stub end separately.
6
Certification & packing — EN 10204 3.1 MTC per component (3.2 witnessed on request), lap faces protected, export-packed.
Lapped Joint Flange Specifications
| Parameter | Details |
|---|
| Size Range | ½″ NB to 56″ NB |
| Pressure Classes | 150#, 300#, 400#, 600#, 900#, 1500#, 2500# |
| Pressure Ratings | PN 1 – PN 400 |
| Standard | ASME B16.5; Stub End to ASME B16.9 |
| Facing Type | Flat Face (flange ring); Stub End lapped face |
| Carbon Steel | ASTM A105 (flange ring); A234 WPB (stub end) |
| LTCS | ASTM A350 LF2 |
| Alloy Steel | ASTM A182 F5, F9, F11, F21, F22, F91 |
| Stainless Steel | ASTM A182 F304/304H/304L, F316/316H/316L/316Ti, F309, F310, F317L, F321, F347, F904L |
| Duplex / Super Duplex | ASTM A182 F51 (2205), F53 (2507), F55 (Zeron 100) |
| Nickel Alloys | UNS N02200, UNS N02201 |
| Monel | UNS N04400, UNS N05500, Alloy 20 |
| Inconel / Incoloy | UNS N06600, N06601, N06625, N08800, N08810, N08825 |
| Hastelloy | UNS N10276, N06022, N10665, N06455 |
| Titanium | Gr.1, Gr.2, Gr.3, DTH 3.7035, DTH 3.7055 |
| Copper Nickel | C70600 (90/10), C71500 (70/30), C71640 |
| Surface Treatments | Hot Dip Galvanizing, Sand Blasting, Shot Peening, Epoxy Coating, FBE Coating |
| Test Certificates | EN 10204 3.1/3.2 MTC, PMI, Hydro Test, RT/UT/PT/MT |
Lapped Joint Flange Dimensions — ANSI / ASME B16.5
ANSI / ASME B16.5 Lapped Joint Flange Dimensions
Lapped Joint Flange vs Weld Neck vs Slip-On
| Factor |
Lapped Joint |
Weld Neck |
Slip-On |
| Bolt Hole Alignment |
360° rotation — easiest alignment |
Fixed — pipe must be rotated |
Fixed — pipe must be rotated |
| Dismantling for Maintenance |
Excellent — ring is loose |
Standard — requires full flange break |
Standard — requires full flange break |
| Mixed Material Option |
Yes — ring and stub end can differ |
No — single piece material |
No — single piece material |
| Fatigue Life |
~1/10th of WN (lower) |
Highest (butt weld, E=1.0) |
Lower than WN |
| Lined Pipe Compatibility |
Excellent (PTFE, rubber, glass) |
Limited |
Limited |
| Typical Use |
Frequent maintenance, corrosive, lined |
High-pressure, cyclic, critical service |
Low/moderate pressure, utilities |
Industries & Applications
| Industry | Typical Application | Stub End Material |
|---|
| Chemical & Petrochemical | Corrosive fluid lines, frequent inspection break-ins | A182 F316L, Hastelloy C276 |
| Food, Beverage & Pharma | Hygienic lines requiring frequent dismantling | A182 F316L (Ra <0.8µm) |
| Cryogenic / LNG | Cold process lines, PTFE-lined cryogenic pipe | A350 LF2, A182 F304L |
| Water Treatment | Large-bore flanging to fixed infrastructure | A105 / A182 F316 |
| Lined Piping Systems | PTFE-lined, rubber-lined, glass-lined pipe | PTFE-faced or alloy stub end |
| Offshore & Marine | Seawater systems, ballast, fire water lines | Duplex 2205, Cu-Ni 90/10 |
Lapped Joint Flanges by Material Grade
How to Specify & Order a Lapped Joint Flange
A lapped joint is ordered as two components — state both, and whether you need us to supply the set or the ring only:
1
Size & standard — nominal bore and flange standard, e.g. 6″ NB ASME B16.5.
2
Pressure class — Class 150/300/600/900/1500/2500.
3
Backing ring material — commonly ASTM A105 carbon steel or galvanised; stainless where the environment demands.
4
Stub end — material to match the pipe (e.g. A403 WP316L, cupronickel, titanium), type per MSS SP-43 Type A/B or ASME B16.9, and pipe schedule.
5
Certification & quantity — EN 10204 3.1 or 3.2 per component, NACE or project specs, quantity and destination — sent to
sales@tescosteel.com or the
inquiry form.
Example of a complete line item: “Lap Joint Flange, 6″ NB, ASME B16.5 Class 150, ring ASTM A105, with stub end A403 WP316L MSS SP-43 Type A, Sch 40, EN 10204 3.1 — 20 sets.”
Frequently Asked Questions — Lapped Joint Flanges
What is a lapped joint flange?▼
A lapped joint flange (LJF), also called a loose flange or backing flange, is a two-piece flanging system: a loose rotating flange ring and a lap joint stub end. The stub end is butt-welded to the pipe; the flange ring slides freely over the pipe and backs up against the stub end's lapped face. Because the ring rotates 360°, bolt holes align with the mating flange without rotating the pipe. Governed by ASME B16.5, available in Class 150 through 2500.
How does a lapped joint flange work with a stub end?▼
The lap joint stub end — a short pipe section with a lapped face at one end — is butt-welded to the pipe. The loose flange ring, threaded onto the pipe before welding, is slid back over the stub end. When bolted up, the ring bears against the back of the stub end's lapped face. The ring does not seal; the sealing gasket sits on the stub end face. Because the ring is loose, it can rotate freely to align with any bolt hole pattern without touching the pipe weld.
What is the main advantage of using a lapped joint flange?▼
The primary advantage is 360° rotation for easy bolt hole alignment. Additional advantages: (1) Easy dismantling for inspection and maintenance without disturbing pipe welds; (2) Material cost savings — use cheap carbon steel flange ring with an expensive alloy stub end (only the stub end contacts the fluid), reducing cost by 40–60%; (3) Compatible with PTFE-lined, rubber-lined, and glass-lined pipe where the liner extends over the stub end face; (4) Ideal for cryogenic and low-temperature services.
When should I use a lapped joint flange instead of a weld neck flange?▼
Use a lapped joint flange when: (1)
Frequent dismantling for inspection or cleaning is required (food, pharma, chemical plants); (2) Bolt hole alignment to fixed equipment is critical and the pipe cannot be rotated; (3) You want to use a
low-cost flange ring with an expensive alloy stub end; (4) The piping is PTFE-lined, rubber-lined, or glass-lined. Use a
weld neck flange when higher fatigue life, higher pressure cycling, or full radiographic weld inspection (E = 1.0) is required.
Can the flange ring and stub end be different materials?▼
Yes — this is one of the key economic advantages of the LJF system. Because only the stub end contacts the process fluid, it must be the appropriate corrosion-resistant alloy (e.g., ASTM A182 F316L, Hastelloy C276, or Titanium Gr.2). The flange ring, which only provides mechanical backing and bolt clamping force, can be made from inexpensive ASTM A105 carbon steel. For highly corrosive services with expensive alloy piping, this material split can reduce flange assembly cost by 40–60%.
What are the pressure and fatigue limitations of lapped joint flanges?▼
Lapped joint flanges have
lower fatigue life and pressure capacity compared to weld neck flanges. Per ASME B31.3, the fatigue life of a lapped joint flange assembly is approximately
one-tenth that of a weld neck flange of the same size and class, because the stub end-to-pipe joint introduces a stress concentration at the lapped face. Lapped joint flanges are therefore not recommended for
cyclic service, high-vibration, or fatigue-critical applications. For these,
weld neck or
long weld neck flanges are preferred.
What ASME standard governs lapped joint flanges?▼
Lapped joint flanges are dimensionally governed by ASME B16.5 — Pipe Flanges and Flanged Fittings (NPS ½–24, Class 150–2500). The lap joint stub end dimensions are covered by ASME B16.9 (factory-made wrought fittings). Pressure-temperature ratings follow ASME B16.5 for the flange class. Material specifications follow ASTM A182 for forged stainless and alloy grades, and ASTM A105 for carbon steel flange rings.
Which industries use lapped joint flanges?▼
LJFs are widely used in: Chemical and Petrochemical Plants (corrosive fluid lines requiring frequent break-ins); Food, Beverage, and Pharmaceutical (hygienic lines requiring regular dismantling and CIP cleaning); Cryogenic and LNG service (LTCS or SS 304L/316L stub ends, PTFE-lined systems); Water Treatment (large-bore flanging to fixed infrastructure where bolt alignment is critical); Lined Piping Systems (rubber-lined, PTFE-lined, glass-lined pipe); and Offshore and Marine (seawater and ballast systems using duplex or Cu-Ni stub ends with carbon steel rings).
Do lap joint backing rings need to match the pipe material?▼
No — and that is the type's whole economy. The backing ring never contacts the process fluid; only the stub end is wetted. So a titanium or cupronickel line can run carbon steel backing rings at a fraction of the alloy cost, with galvanised rings common in marine service. Match the ring material to the environment (corrosion from the outside) and the bolting practice, not to the fluid. The stub end always matches the pipe.
How much does a lapped joint flange weigh?▼
The backing ring weighs slightly less than a slip-on flange of the same size and class — it is a plain ring with no facing. As working approximations for carbon steel ASME B16.5 backing rings: a 2" Class 150 weighs about 2 kg, a 6" Class 150 about 7 kg, and a 12" Class 150 about 22 kg — plus the stub end, which is quoted with the set. Every quotation states exact component weights.
What is the difference between MSS SP-43 Type A and Type B stub ends?▼
Type A stub ends are made for use with lap joint flanges: the lap face is machined with a serrated gasket finish and the corner radius suits the backing ring's bore radius. Type B are made for use with plate or slip-on flanges used as backing rings: the lap corner is square-cut. Long and short patterns exist in both. State the flange you are backing with and we supply the matching type — mixing them can leave the lap unsupported at the radius.
Can lapped joint flanges be reused when piping is dismantled?▼
Yes — this is one of the type's advantages in maintenance-heavy service. The backing ring is not welded to anything, so when the joint is broken the ring slides back and survives; wear and corrosion concentrate on the replaceable stub end. Frequent-dismantling duties — strainers, exchangers on cleaning cycles, glass-lined and PTFE-lined systems — profit from rings that live through many gasket changes.
What details are needed to get an accurate lapped joint flange quotation?▼
Five elements plus commercial terms: (1) size and standard — e.g. 6" NB ASME B16.5; (2) pressure class; (3) backing ring material — e.g. ASTM A105, galvanised, or stainless; (4) stub end — material (e.g. A403 WP316L), type (MSS SP-43 Type A/B or ASME B16.9) and pipe schedule, or state 'ring only' if you source stub ends elsewhere; (5) certification — EN 10204 3.1 or 3.2 per component, NACE or project specs. Add quantity and destination and we return price, weight and delivery — normally within 24 hours.
Who manufactures lapped joint flanges in India?▼
Tesco Steel & Engineering is an ISO 9001:2015 certified flange manufacturer based in Mumbai, India, producing lap joint backing rings and matching stub ends across the material range — carbon steel A105, stainless and duplex A182 grades, nickel alloys, cupronickel and titanium. Components are made to ASME B16.5, ASME B16.9 and MSS SP-43, supplied with EN 10204 3.1/3.2 certification per component, and exported to more than 50 countries.
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ISO-certified manufacturer & exporter. ASME B16.5 Class 150–2500. All materials — carbon steel, SS, alloy, Inconel, Hastelloy, Titanium. Fast delivery worldwide from Mumbai, India.
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