This reference page provides the dimensional and connection information for a Weld Neck Flange 3/4 Inch Class 400. Use the source data below when checking flange geometry, bolt-hole details, stud selection, and drawing requirements for piping work.
Because a weld neck flange is welded directly to the pipe, accurate coordination between the flange, pipe outside diameter, wall thickness, bore, gasket, and bolting is important. The listed dimensions should therefore be read together with the project piping specification and the selected pipe schedule.
Weld Neck Flange 3/4″ Class 400
Weld Neck Flange 3/4″ Class 400 is widely used in piping systems that require strong, leak-resistant flange connections. It features a long tapered hub that provides excellent stress distribution and is commonly applied in process piping, utility lines, and industrial systems where welding strength and reliability are important.
This dimension data is based on ANSI / ASME B16.5-2020.
Weld Neck Flange 3/4″ Class 400 Dimensions
- Reference Standard: ANSI / ASME B16.5
- Nominal Pipe Size (NPS):3/4″
- DN Size: DN20
- Outside Diameter:117mm
- Flange Thickness:15.7mm
- Hub Diameter:48mm
- Bore Diameter: varies depending on pipe schedule and pipe wall thickness
- Raised Face Diameter:42.9mm
- Weight: 1.5kg
- Number of Bolts:4
- Stud Bolt Size: 5/8″ UNC (or M16) x 90 Long
- Hole Diameter: 3/4″ (19.05mm)
What Is a Weld Neck Flange?
A weld neck flange is a type of pipe flange designed with a long tapered hub that is welded directly to the pipe. This design helps reduce stress concentration at the flange base and provides better strength under pressure, temperature fluctuation, and cyclic loading.
Common Applications
Weld Neck Flange 3/4″ Class 400 is commonly used for:
- Process piping systems
- Oil and gas lines
- Water and utility piping
- Higher pressure service
- Pressure piping connections
- Industrial fabrication and maintenance work
CAD Drawing Download
This page includes the CAD drawing file for Weld Neck Flange 3/4″ Class 400, which can be used for drafting, detailing, piping layout coordination, and fabrication reference.
Available Weld Neck Flange Class 400 Sizes
This size is part of the Weld Neck Flange Class 400 series. Check other sizes in the same category to find matching dimension data and CAD files for your project.
Notes
Before fabrication or installation, always confirm the latest project requirements, flange material specification, pipe schedule, bore size, gasket type, bolt length, and applicable pressure-temperature rating.
How to Read the Weld Neck Flange Reference
The dimensional list identifies the nominal pipe size, metric designation, outside diameter, thickness, hub diameter, raised-face diameter, bolt quantity, stud size, and hole diameter. These values describe the flange component and its connection geometry; they do not by themselves establish whether an assembled joint is acceptable for a particular service.
Why the Bore Requires Attention
The bore is identified as dependent on the pipe schedule and wall thickness. This is a key fabrication check because the flange must align with the pipe interior without creating an unintended restriction, excessive mismatch, or interference at the weld. Confirm the bore against the actual pipe specification before ordering, machining, or preparing a fabrication drawing.
Weld Neck Hub and Stress Transfer
The tapered hub provides a gradual transition between the flange and the pipe. Compared with a flange that does not use an extended hub, this geometry is intended to support a more controlled transfer of load into the welded connection. Final suitability still depends on the piping design, material, temperature, loading, welding procedure, and applicable project requirements.
Bolting and Joint Assembly Checks
The reference identifies the bolt count, stud designation, stud length, and hole diameter. Check that the selected studs, nuts, washers where specified, gasket, flange facing, and tightening procedure are compatible with one another. Bolt length should be verified against the actual flange pair, gasket thickness, washers, and available thread engagement rather than assumed from the flange listing alone.
Using the CAD File
The downloadable DWG can support drafting, layout coordination, detailing, and fabrication reference. Treat the drawing as a dimensional aid and coordinate it with the authoritative flange data, pipe schedule, gasket arrangement, orientation requirements, and project drawing standards. CAD geometry should not replace a final dimensional and material review.
Related Pipe and Flange References
- Compare this entry with other Class 400 weld neck flange sizes when developing a consistent piping library.
- Review related pipe schedule and bore references before selecting the flange bore.
- Use the site’s flange terminology and facing references to distinguish weld neck, slip-on, socket-weld, threaded, and blind configurations.
- Coordinate the flange with related CAD/DWG piping resources during layout and fabrication documentation.
Frequently Asked Questions
What is a weld neck flange?
A weld neck flange is a pipe flange with a tapered hub that is welded directly to the pipe. The hub provides a gradual transition intended to reduce stress concentration at the flange-to-pipe connection.
What does the Class 400 designation mean?
The class designation identifies the flange pressure-class category used for specification and selection. It is not a complete service approval by itself; pressure-temperature capability also depends on material, temperature, joint details, and the governing project requirements.
Why does the bore vary with pipe schedule?
Pipe schedules use different wall thicknesses for a given nominal size. Since the flange bore must coordinate with the pipe inside diameter and wall thickness, the required bore should be confirmed against the actual pipe specification.
Can the listed stud size be used for every installation?
The listed stud size and length are reference details for this flange entry. Verify the complete bolted joint, including the mating flange, gasket, washers, nut arrangement, coating, thread engagement, and project tightening requirements.
What should be checked before fabrication?
Confirm the flange standard, material specification, pipe schedule, bore, facing, gasket, bolt length, welding requirements, and applicable pressure-temperature criteria. Also check that the CAD file and fabrication drawings match the approved project information.
Is the DWG file suitable for final fabrication without review?
No. The DWG is intended to support drafting and coordination. It should be reviewed against the source dimensions, the selected pipe and gasket details, the mating flange, and the project’s approved engineering documentation.