Stainless Steel Stub End for Lap Joint Flange Connections
The stainless steel stub end is a butt-weld fitting used with a lap joint flange to create removable and serviceable flanged connections. The stub end is welded to the pipe, while the lap joint flange can rotate freely around it, making bolt-hole alignment easier during installation.
As part of Nonleak’s butt-weld fittings range, lap joint stub ends are suitable for heat exchangers, reactors, pump connections, valve connections and equipment areas that require regular inspection, cleaning or maintenance.
How the Stub End & Lap Joint Flange System Works
A stub end and lap joint flange work together as a two-part flanged connection. Each component has a different function during welding, sealing and maintenance.
| Component | Function |
| Stub End | Butt-welded to the pipe end, providing the sealing face and transition to the flange |
| Lap Joint Flange | Slides freely over the stub end, rotates for bolt alignment, and does not contact the process fluid |
| Sealing Surface | The stub end’s raised face (or flat face) creates the gasket sealing surface against the mating flange |
Key Advantages of Using Stub Ends
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Lower Material Cost: Lap joint flanges can reduce cost in high-alloy piping systems because the flange does not contact the process fluid.
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Simplified Alignment: The rotating flange helps installers align bolt holes during field installation.
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Easy Maintenance: The connection can be disassembled for inspection or cleaning without cutting the pipe.
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Reduced Stress Concentration: The butt-weld end provides a secure pipe connection for serviceable flange assemblies.
Engineering Features of Butt-Weld Stub Ends
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Seamless or Welded Construction: Available according to size, wall thickness and project requirements.
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Precision Machined Lap Face: Provides a smooth sealing surface for gasket contact.
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Consistent Wall Thickness: Helps maintain strength through the transition area.
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Beveled Weld End: Prepared for standard field welding to pipe.
Material Options for Stainless Steel Stub Ends
| Material Grade | Key Properties | Typical Applications |
| 304/304L | Excellent corrosion resistance, good formability | General chemical, food processing, water treatment |
| 316/316L | Superior chloride resistance, higher strength | Marine, pharmaceutical, coastal facilities |
| Duplex 2205 | Twice the yield strength of 316L, excellent SCC resistance | Offshore platforms, desalination, sour service |
| Duplex 2507 | Super duplex, extreme corrosion and pitting resistance | Highly aggressive chemical, high‑chloride environments |
Global Standard Compliance
Nonleak manufactures stainless steel stub end products according to project specifications and applicable butt-welding fitting standards, including ASME B16.9.
All stub ends are manufactured and tested to meet or exceed:
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ASME B16.9: Factory-made wrought buttwelding fitting dimensions
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ASTM A403/A403M: Wrought austenitic stainless steel pressure piping fittings
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DIN / ISO / JIS options: Available according to project requirements
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SH3408 / SH3409 / SH3410 – Petrochemical Industry Standards
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HG/T21635, DL/T695, SY/T0510 – Industry-Specific Standards
Cross-section Diagram
Specification Table
| Nominal Pipe Size (NPS) | Outside Diameter At Bevel D (mm) | Outside Diameter of Barrel(mm) | Length F(mm) | Radius of Fillet R(mm) | Diameter of Lap G(mm) | |||
| Min. | Max. | ASME | MSS | ANSI & MSS Type A | MSS Type B | |||
| 1/2 | 21.3 | 20.55 | 22.76 | 76.2 | 50.8 | 3 | 0.8 | 35 |
| 3/4 | 26.7 | 25.88 | 28.09 | 76.2 | 50.8 | 3 | 0.8 | 42.9 |
| 1 | 33.4 | 32.61 | 34.95 | 101.6 | 50.8 | 3 | 0.8 | 50.8 |
| 1-1/4 | 42.2 | 41.38 | 43.59 | 101.6 | 50.8 | 4.8 | 0.8 | 63.5 |
| 1-1/2 | 48.3 | 47.47 | 49.94 | 101.6 | 50.8 | 6.4 | 0.8 | 73.2 |
| 2 | 60.3 | 59.54 | 62.38 | 152.4 | 63.5 | 7.9 | 0.8 | 91.9 |
| 2-1/2 | 73 | 72.24 | 75.34 | 152.4 | 63.5 | 7.9 | 0.8 | 104.6 |
| 3 | 88.9 | 88.11 | 91.34 | 152.4 | 63.5 | 9.7 | 0.8 | 127 |
| 3-1/2 | 101.6 | 100.81 | 104.04 | 152.4 | 76.2 | 9.7 | 0.8 | 139.7 |
| 4 | 114.3 | 113.51 | 116.66 | 152.4 | 76.2 | 11.2 | 0.8 | 157.2 |
| 5 | 141.3 | 140.51 | 144.35 | 203.2 | 76.2 | 11.2 | 1.5 | 185.7 |
| 6 | 168.3 | 167.49 | 171.27 | 203.2 | 88.9 | 12.7 | 1.5 | 215.9 |
| 8 | 219.1 | 218.29 | 222.07 | 203.2 | 101.6 | 12.7 | 1.5 | 269.7 |
| 10 | 273.1 | 272.26 | 277.19 | 254 | 127 | 12.7 | 1.5 | 323.9 |
For complete dimensional data for all sizes (DN10–DN600), download our Butt-Weld Stub End Technical Documentation.
Key Applications
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Heat Exchangers: Removable tube bundles, maintenance access
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Chemical Processing: Reactors, vessels requiring frequent cleaning
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Pharmaceutical: Sanitary connections, equipment disconnection
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Food & Beverage: CIP (clean-in-place) systems
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Oil & Gas: Modular equipment connections, skid assemblies
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Power Generation: Turbine connections, serviceable joints
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Water Treatment: Pump and valve connections
Quality Assurance & Testing
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Material Traceability: Mill certificates provided for all raw materials
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Dimensional Inspection: 100% inspection to ASME B16.9 / GB/T12459 tolerances
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Surface Finish Verification: Sealing face flatness and finish inspected per standard
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Non-Destructive Testing: RT/UT/PT/MT available upon request
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Mechanical Testing: Tensile strength, hardness, flattening tests per batch
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Chemical Analysis: Verification of material composition
Custom Options
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Special Materials: Other grades available upon request
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Non-Standard Dimensions: Custom lengths and face dimensions
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Face Finish: Raised face (RF) or flat face (FF) available
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End Preparation: Beveled ends standard; special preparations available
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Marking: Laser marking per customer specification
