Lap Joint Flange & Stub End Manufacturer in India | LJ / LJF / LJFF | ASME B16.5 | Remax Forge
Key Features
Two-piece assembly — Backing Flange + Stub End
The backing flange is NOT welded to the pipe. Only the stub end (welded to pipe) contacts the fluid — enabling exotic alloy savings.
360° free rotation — solves bolt hole alignment
The backing flange rotates freely through 360° around the stub end — aligns bolt holes to any position after all welds are complete.
40–60% cost saving on exotic alloy pipelines
Only the stub end (in contact with fluid) needs expensive alloy. The backing flange (external only) stays in Carbon Steel A105.
🔄 How the Lap Joint Assembly Works
1. Stub End
Short piece of pipe with a flared/lapped end — welded to the pipe. Must be in the same material as the pipe (it contacts the fluid). Available as Short Pattern (ASME B16.9) or Long Pattern.
2. Backing Flange
Flat-faced, hubless flange that slides freely over the pipe. NOT welded — it laps over the stub end radius. Can be Carbon Steel A105 even on exotic alloy pipelines. Rotates 360° freely.
Note: Gasket sits between the two Stub End faces (not on the backing flanges). The Stub End radius IS the sealing surface.
What is a Lap Joint Flange?
A Lap Joint Flange (LJ Flange) is a TWO-PIECE assembly consisting of: (1) the Lap Joint Backing Flange — a flat-faced, hubless flange that slides freely over the pipe, and (2) a Stub End — a short piece of pipe with a flared/lapped end that is butt-welded to the pipe.
The backing flange is NOT welded to the pipe. It simply "laps" over the radius of the stub end. This creates two powerful advantages found in no other flange type: free 360° rotation for perfect bolt hole alignment, and significant material cost savings on exotic alloy pipelines.
Industry Abbreviations
✅ Backing Flange Material
Use Carbon Steel A105 for the backing flange in almost all cases — it never contacts the process fluid.
🔬 Stub End Material
Must match the pipe material — it is butt-welded to the pipe and contacts the fluid directly.
🔗 For high-pressure critical service, see our Weld Neck Flange. Compare our complete flange range.
Standard Specifications
Complete specifications for the Lap Joint Flange assembly (backing flange + stub end):
| Property | Detail |
|---|---|
| Product Names | Lap Joint Flange, LJ Flange, Loose Flange, Backing Flange + Stub End Assembly |
| Size Range | ½" (15 NB) to 60" (1500 NB) |
| Pressure Classes | 150#, 300#, 400#, 600#, 900#, 1500#, 2500# (ASME B16.5) |
| Backing Flange Face | Always Flat Face (LJFF) — backing flange has no raised face |
| Sealing Face | The "lap" radius of the Stub End acts as the sealing surface |
| Standards | ASME B16.5 (backing flange), ASME B16.9 (stub ends), MSS SP-43 (light gauge stub ends) |
| Stub End Types | Short Pattern (ASME B16.9) or Long Pattern; specify when ordering |
| Cost Advantage | Backing Flange in Carbon Steel A105; Stub End in exotic alloy = 40–60% cost saving |
| Rotation | Backing flange rotates 360° freely over pipe — unlimited bolt hole alignment |
| MTC | EN 10204 3.1 for both backing flange and stub end; 3.2 on request |
| Lead Time | 7–14 days standard; custom alloy stub ends 3–6 weeks |
Lap Joint Flange Material Grades
We manufacture Stub Ends in all alloys to match pipe material. Backing Flanges are typically Carbon Steel A105. Both components available in Stainless Steel, Duplex, Super Duplex, Nickel Alloys, and more:
| Material Category | Grades / Specifications |
|---|---|
| Stainless Steel Lap Joint Flanges | ASTM/ASME A/SA182: F304, F304L, F316, F316L, F316H, F316Ti, F321, F347; Cast: CF3, CF3M, CF8, CF8M; DIN: 1.4301, 1.4306, 1.4401, 1.4404, 1.4408, 1.4409 |
| Duplex Steel Lap Joint Flanges | UNS S31803/S32205 — ASTM A182 Gr F51, F52, F53, F54, F55, F57, F59, F60, F61 |
| Super Duplex Lap Joint Flanges | UNS S32750/S32760 — ASTM A182 Gr F53, F55; Zeron 100 |
| Carbon Steel Lap Joint Flanges | ASTM/ASME A/SA105, A105N, A216-WCB; A350 LF2 (low temp); A694 F52/F56/F60/F65/F70/F80 (high yield); DIN 1.0460, 1.0402, 1.0619 |
| Alloy Steel Lap Joint Flanges | ASTM A182/ASME SA182: F5, F9, F11, F12, F22, F91 (all P-grades for high temp service) |
| Nickel Alloy Lap Joint Flanges | Inconel 600, 601, 625, 718, 690, X750 (ASTM B564/ASME SB564); Incoloy 800, 800H, 800HT, 825, 925 |
| Hastelloy Lap Joint Flanges | C276 (UNS N10276), C22 (UNS N06022), C4, C2000, B2, B3, X (ASTM B564) |
| Monel Lap Joint Flanges | Monel 400 (UNS N04400), Monel K500 (UNS N05500) — ASTM B564 |
| Pure Nickel Lap Joint Flanges | Nickel 200, 201, 205, 205LC — ASTM B564/ASME SB564 |
| Copper Nickel Lap Joint Flanges | CuNi 90/10 (C70600), CuNi 70/30 (C71500), UNS C71640 — ASTM/ASME SB 61/62/151/152 |
| Titanium Lap Joint Flanges | Gr.1, Gr.2, Gr.4, Gr.5, Gr.7 — ASTM B381/ASME SB381; R50250/R50400/R50550/R50700/R52400/R53400/R56400 |
| Aluminium Lap Joint Flanges | 5052, 6061, 6063, 2017, 7075 |
| Brass Lap Joint Flanges | 3602, 2604, H59, H62 |
| Special Alloy Lap Joint Flanges | Alloy 20 (ASTM B462 SB462 — Carpenter 20Cb-3); SMO 254/6Mo (UNS S31254, DIN 1.4547); Al6XN; AISI 4130; AISI 4140; Nimonic 75/80A/90; Gunmetal; Cast Iron |
Forged Raw Billets stockLap Joint Flange Standards & Specifications
Backing flanges per ASME B16.5; stub ends per ASME B16.9 (short/long pattern) and MSS SP-43:
| Standard / Spec | Scope / Application Details |
|---|---|
| 🇺🇸ANSI/ASME B16.5 | NPS ½" to 24" — the primary standard for most flanges |
| 🇺🇸ASME B16.47 Series A (MSS SP-44) | NPS 26" to 60" — large diameter |
| 🇺🇸ASME B16.47 Series B (API 605) | NPS 26" to 60" — large diameter (lighter) |
| 🇺🇸ASME B16.36 | Orifice flanges |
| 🇺🇸ASME B16.48 | Line blinds & spectacle blinds |
| 🇪🇺DIN 2501 / EN 1092-1 | European metric standard — PN ratings |
| 🇯🇵JIS B2220 | Japanese Industrial Standard |
| 🇬🇧BS 4504 / BS 10 Table D/E/F/H | British Standard |
| 🇺🇸MSS SP-44 | Large diameter steel pipeline flanges |
| 🇺🇸API 6A | Wellhead and Christmas tree equipment |
| 🇺🇸API 605 | Large diameter carbon steel flanges |
| 🇺🇸AWWA C207 | Water works flanges |
| 🇷🇺GOST 12820 / 12821 | Russian/CIS standard |
| 🇦🇺AS 2129 / AS 4087 / AS/NZS 4331.1 | Australian standard |
| 🇰🇷KS B1503 | Korean standard |
| 🌐ISO 7005-1 / ISO 9624 | International standard |
| 🇺🇸SAE J518 | Hydraulic flanged tube fittings |
| 🇨🇳GB Standard | Chinese national standard |
ASME B16.5 Lap Joint Flange Dimensions Table
Class 150# backing flange dimensions — same OD, bolt circle, and bolt holes as Slip-On/Weld Neck of same class. Dimensions per ASME B16.5. Weights are approximate for Carbon Steel A105:
Order separately: (1) Backing Flange — size, class, material; (2) Stub End — size, material (must match pipe), short or long pattern. Contact us for matched pair pricing.
NPS (inch)↕ | Backing Flange OD (mm)↕ | Bolt Circle (mm)↕ | No. Bolts↕ | Bolt Ø (mm)↕ | Backing Flange Thickness (mm)↕ | Stub End OD at Lap (mm)↕ | Short Stub End Length (mm)↕ | Approx Wt Backing CS (kg)↕ |
|---|---|---|---|---|---|---|---|---|
| ½ | 89 | 60 | 4 | 16 | 11.2 | 33.4 | 38 | 0.4 |
| 1 | 108 | 79 | 4 | 16 | 12.7 | 48.3 | 51 | 0.6 |
| 2 | 152 | 121 | 4 | 19 | 15.9 | 73.0 | 64 | 1.2 |
| 3 | 190 | 152 | 4 | 19 | 19.1 | 101.6 | 76 | 2.5 |
| 4 | 229 | 190 | 8 | 19 | 22.4 | 127.0 | 89 | 4.0 |
| 6 | 279 | 241 | 8 | 22 | 25.4 | 184.2 | 102 | 7.0 |
| 8 | 343 | 298 | 8 | 22 | 28.6 | 238.2 | 114 | 11.5 |
| 10 | 406 | 362 | 12 | 25 | 30.2 | 295.3 | 127 | 17.5 |
| 12 | 483 | 432 | 12 | 25 | 31.8 | 346.1 | 152 | 25.0 |
| 16 | 597 | 540 | 16 | 29 | 36.6 | 450.9 | 178 | 45.0 |
| 20 | 699 | 635 | 20 | 32 | 42.9 | 552.5 | 203 | 74.0 |
| 24 | 813 | 749 | 20 | 35 | 47.8 | 655.3 | 229 | 108.0 |
* Dimensions shown are for the backing flange. Stub end dimensions (lap OD and length) are listed separately. Order backing flange and stub end as matched pair — contact us for combined pricing.
Flange Face Types
The Lap Joint backing flange is always Flat Face (LJFF). The sealing surface is provided by the Stub End lap radius — not the backing flange face. The gasket contacts the two Stub End faces.
Raised Face (RF)
Most common. A raised circular ring that concentrates pressure on a smaller area to compress the gasket. Height: 1/16" for Class 150/300; 1/4" for Class 400 and above.
Flat Face (FF)
No raised portion; entire flange face is in the same plane. Used when mating against cast iron or non-metallic flanges to avoid cracking on bolt tightening.
Ring Type Joint (RTJ)
Oval or octagonal groove machined into the face; a metal ring gasket seats in the groove. Used in high-pressure, high-temperature critical service (refineries, oil fields).
Tongue & Groove (T&G)
One flange has a raised ring (tongue); the other a matching groove. Provides excellent alignment and a confined gasket. Used in pumps and valve bonnets.
Male & Female (M&F)
Similar to T&G but the female face is flat and the male face raised. Used in heat exchangers, pressure vessels, and high-integrity process joints.
Large Male & Female
Same operating principle as the standard Male & Female flange, scaled up with larger step contact surfaces for specialized heavy industrial equipment.
Why Choose Lap Joint Flange?
360° Free Rotation
Backing flange rotates freely — eliminates bolt hole alignment problems in cramped spaces or long pipe runs with cumulative misalignment.
40–60% Cost Saving
Carbon Steel backing flange + expensive alloy stub end = significant saving on Duplex, Inconel, Hastelloy, and Monel pipelines.
Easy Inspection
Back off the backing flange and inspect or replace the stub end WITHOUT cutting the pipe or breaking the weld.
Frequent Dismantling
Ideal for systems requiring regular disassembly for cleaning, inspection, catalyst change, or process modifications.
Lined Piping Compatible
For FRP, PTFE-lined, rubber-lined, or enamel-lined pipes where direct welding to the flange face is not possible.
Corrosive Service
Stub end in corrosion-resistant alloy (contacting fluid); backing flange in cheap Carbon Steel (external only).
Industries & Applications
✓ Primary Applications
Oil & Gas
Upstream extraction, midstream pipelines, downstream refineries.
Petrochemical
Chemical reactors, process lines, heat exchangers.
Power Generation
Boilers, steam turbines, nuclear plants, thermal power.
Pharmaceuticals
Hygienic piping, clean steam, pure water systems.
Food & Beverage
Sanitary flanges, sugar mills, beverage processing.
Paper & Pulp
Chemical recovery, bleaching lines.
Water Treatment
Municipal water, desalination, irrigation.
Shipbuilding
Offshore platforms, FPSOs, marine piping.
Chemical Plants
Acid service, caustic lines, solvent handling.
Construction
HVAC, fire suppression, utility headers.
Testing & Inspection
Zero-defect quality control — visual inspection, dimensional checking, PMI, UT, hydrostatic testing. Stub end weld tested separately from backing flange.
Hydrostatic / Hydro Pressure Test
Each flange pressure tested at 1.5x working pressure per ASME code requirements.
Ultrasonic Testing (UT)
Non-destructive testing to detect internal sub-surface cracks, inclusions and forging defects.
Radiographic Testing (RT / X-Ray)
100% radiography available; mandatory for critical Class 900+ high pressure services.
Positive Material Identification (PMI)
Spectrometer validation to verify alloy chemistry precisely matches the Mill Test Certificate.
Dye Penetrant Test (DPT / LPT)
Detects micro surface cracking and porosity on critical machined seating surfaces.
Magnetic Particle Inspection (MPI)
For ferromagnetic alloys; flags surface and near-surface structural discontinuities.
Hardness Test (Brinell/Rockwell)
Verifies correct heat treatment structure and ensures mechanical properties are hit.
Direct-Reading Spectrograph
In-house lab chemical checks of billets before forging process begins.
Impact / Charpy Test
Crucial for low-temperature applications to verify ductility (e.g. A350 LF2, LTCS).
NACE Compliance Testing
Verifies sour-gas / H2S environment service capability (NACE MR0175 / MR0103).
Documents & Certificates
Full documentation for both components — separate MTCs for backing flange and stub end. EN 10204 3.1 standard; 3.2 on request.
Mill Test Certificate (MTC)
Provided as per EN 10204 3.1 detailing chemical & mechanical analysis.
EN 10204 3.2 Certificate
Independent third-party inspection validation (available upon request).
NACE MR0175 / MR0103 Compliance
Certified suitability for sour gas/H2S environments.
Raw Materials Certificate
Provides 100% trace origin tracking from steel billet to finished flange.
Dimensional Inspection Report
All critical tolerances checked and certified against CAD designs.
Heat Treatment Certificate
HTR and PWHT thermal chart records included where requested.
Hydrostatic Test Certificate
Pressure log documentation verifying weld integrity.
Third Party Inspection (TPI)
Bureau Veritas, SGS, Lloyds, DNV, TUV inspection options.
Packing List & Weight Certificate
Proper documentation for simple custom clearance and cargo log.
Country of Origin Certificate
Enables import tariff relief and compliance logging.
Lap Joint Flange vs Other Flange Types
Quick comparison to help you decide if Lap Joint is the right choice for your application:
| Feature | Lap Joint Flange | Weld Neck | Slip On |
|---|---|---|---|
| Bolt Hole Alignment | 360° free rotation — always perfect | Fixed — must be aligned during fit-up | Fixed — must be aligned during fit-up |
| Material Cost (exotic alloy) | Lowest — CS backing + alloy stub end only | Highest — full flange in alloy | High — full flange in alloy |
| Inspection / Replacement | Slide back and inspect without cutting | Must cut weld to disassemble | Must cut weld to disassemble |
| Lined Pipe Compatible? | ✅ Yes — no flange-to-pipe weld contact | No | No |
| Weld Required? | Yes — stub end welded to pipe | Yes — butt weld to pipe | Yes — 2 fillet welds |
| Pressure Rating | All classes (150#–2500#) | All classes — code preferred for high P | Up to 600# preferred |
| Best For | Exotic alloys, frequent dismantling, tight spaces | Critical/cyclic/high-pressure | General/moderate service |
Surface Finish & Coating Options
Anti-rust Paint
Standard protection coat applied on carbon steel flanges.
Oil Black Paint
High-grade finish offering superior long-term storage corrosion block.
Yellow Transparent Lacquer
Allows technical inspectors to visually inspect metal surface during receiving.
Zinc Plated
Electro-galvanized bright zinc barrier layer for light industrial environments.
Hot Dip Galvanized (HDG)
Thick zinc alloy barrier layer for maximum outdoor marine rust protection.
Epoxy Coating
FBE or liquid epoxy coating for heavy buried pipelines and sewage lines.
Bare/Pickled & Passivated
Chemical acid cleaning to restore corrosion resistance for stainless steel.
Custom Coating
Special finishes customized exactly to customer painting specifications.
Export Markets
Global Export Network
Why Choose Remax Forge?
Remax Forge & Fittings stands out as a leading flange manufacturer due to our complete in-house forging, heat treatment, and precision CNC machining capabilities based in Mumbai. We provide certified compliance, factory-direct wholesale pricing, and custom forging schedules tailored to your engineering blueprints. With over 20 years of manufacturing experience, zero-defect quality management, and short lead times, we are a trusted supply partner for critical industrial piping projects.
ISO 9001:2015 Certified
Fully audited quality management workflows.
In-House Forging
Forging, heat-treat, machining in Mumbai.
Testing Laboratory
PMI, Spectro, UT, Hydro labs on-site.
Mill Certificates
EN 10204 3.1 standard; 3.2 available.
20+ Years Experience
Serving critical gas/oil clients globally.
45+ Export Countries
Proven global logistics and documentation.
Custom Forging
Special shapes, alloys and schedules.
Factory-Direct Price
Competitive pricing with no agent markup.
Technical Support
Engineers ready to assist spec selection.
Short Lead Times
Fast turnaround of custom and stock orders.
📥 Download Lap Joint Flange Catalogue (PDF)
Complete technical catalogue including backing flange and stub end dimension tables, material grades, standards, and ordering guide.
How to Order
Ordering high-quality forged flanges from Remax is straightforward. To ensure our engineering team provides you with a precise and competitive quote, please specify the exact flange type, nominal pipe size (NPS), pressure class rating, material grade, and facing configuration. Let us know your total quantity requirements and if you require any specialized testing or custom coatings. Contact us via email or phone for a quick, same-day response.
Direct Inquiries
Estimated Lead Times
Frequently Asked Questions
Common questions about Lap Joint Flanges — ordering stub end separately, backing flange material choice, short vs long pattern, and pressure classes.
Related Products
Compare our complete range of industrial flanges for your piping project.
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Tapered neck for high pressure and temperature service.
Blind Flange
Bolts onto line to isolate sections securely.
Socket Weld Flange
Shoulder socket. Great for high-pressure small lines.
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