This reference page provides the published dimensions and drafting information for a Weld Neck Flange 18 Inch Class 900. Use the dimensional list below when checking flange layouts, preparing piping details, or coordinating the flange with a pipe, gasket, and bolting arrangement.
The most important selection issue is that the listed bore is not a single universal value. It varies with the pipe schedule and wall thickness, so the flange should be matched to the actual pipe specification before fabrication or installation. The CAD file can support layout and detailing work, but it does not replace project-specific verification.
Weld Neck Flange 18″ Class 900
Weld Neck Flange 18″ Class 900 is widely used in piping systems that require strong, leak-resistant flange connections under high-pressure service. It features a long tapered hub that provides excellent stress distribution and is commonly applied in process piping, utility lines, refineries, power plants, and industrial systems where welding strength and reliability are essential.
This dimension data is based on ANSI / ASME B16.5-2020.
Weld Neck Flange 18″ Class 900 Dimensions
- Reference Standard: ANSI / ASME B16.5
- Nominal Pipe Size (NPS):18″
- DN Size: DN450
- Outside Diameter:787mm
- Flange Thickness:101.6mm
- Hub Diameter:565mm
- Bore Diameter: varies depending on pipe schedule and pipe wall thickness
- Raised Face Diameter:533.4mm
- Weight: 367kg
- Number of Bolts:20
- Stud Bolt Size: 1 7/8″ UNC (or M48) x 325 Long
- Hole Diameter: 2″ (50.8mm)
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 18″ Class 900 is commonly used for:
- Process piping systems
- Oil and gas lines
- Refinery and petrochemical piping
- Very high-pressure service
- Pressure piping connections
- Industrial fabrication and maintenance work
CAD Drawing Download
This page includes the CAD drawing file for Weld Neck Flange 18″ Class 900, which can be used for drafting, detailing, piping layout coordination, and fabrication reference.
Available Weld Neck Flange Class 900 Sizes
This size is part of the Weld Neck Flange Class 900 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 flange dimensions
The nominal pipe size identifies the intended pipe connection, while the outside diameter and flange thickness describe the main flange envelope. The hub diameter relates to the tapered welded neck, which transitions from the flange body toward the pipe. This hub is a defining feature of a weld neck flange and should be represented correctly in fabrication and piping drawings.
The raised face diameter identifies the gasket-contacting face configuration shown in the reference data. It should be reviewed together with the selected gasket type and the mating flange. The bore requires additional attention because its final fit depends on pipe wall thickness and schedule; using the nominal size alone is not enough to confirm the opening.
Bolting and installation checks
The source data identifies the bolt quantity, stud bolt size, bolt length, and hole diameter for this flange. These values are useful for preparing a bolt-circle detail, checking clearance, and coordinating flange assembly. Confirm the bolting specification against the project standard before ordering materials, particularly where inch and metric designations are both shown.
Flange weight is also relevant during handling, support planning, and installation. It should be considered with the connected pipe, valve or fitting, gasket, and bolting rather than treated as the complete assembled connection weight.
Using the CAD reference
The downloadable DWG can be useful for piping layout coordination, flange detailing, fabrication reference, and CAD library development. Before using the drawing in a released document, verify units, layer conventions, bore geometry, facing details, and any project drafting requirements. Related pages for Class 900 flange dimensions, weld neck flange sizes, pipe schedules, and flange terminology can help with comparison and specification review.
Frequently asked questions
What does the bore depend on?
The bore varies according to the connected pipe schedule and pipe wall thickness. Confirm the pipe specification before selecting or fabricating the flange.
Why is this flange called a weld neck flange?
It has a long tapered hub that is welded directly to the pipe. The geometry is intended to provide a gradual transition between the flange and pipe.
What information is provided for the bolt connection?
The reference data lists the number of bolts, stud bolt size, bolt length, and hole diameter. Check these details against the applicable project and material requirements before installation.
Can the DWG be used for fabrication?
The DWG is provided as a drafting and fabrication reference. Confirm the drawing units, bore, facing, material requirements, and project tolerances before releasing fabrication information.
Does the listed weight include the complete connection?
No assumption should be made that it represents the assembled pipe connection. Review the flange weight together with the connected components and installation requirements.