Overview
A flange is a projecting rim or ring used to create a bolted connection between pipe, fittings, valves, equipment, or pressure vessels. In a piping joint, two compatible flange faces clamp a gasket or another approved sealing element using bolts or studs. The word “flanged” means that a component is supplied with one or more flange-type end connections.
A complete flange definition includes more than shape. Industrial flanges are identified by a dimensional standard, nominal size, pressure class or PN, type, facing, material, bore, and inspection requirements.
Why It Matters for Pipe Components
Flanged joints provide removable access for installation, maintenance, valve replacement, equipment connection, cleaning, and isolation. Performance depends on the complete joint: both flanges, gasket, bolting, alignment, surface condition, assembly method, pressure, temperature, and external loads.
Two flanges can have the same nominal size but different drilling, OD, facing, thickness, or rating. Class 150, PN16, JIS 10K, and other designations are not interchangeable labels. Compatibility must be checked against the applicable standards.
The flange material also does not define the rating by itself. Pressure-temperature capability comes from the standard, material group, temperature, and design basis.
Methods, Parameters, or Process
Common flange types are selected according to connection method and service.
| Flange type | Connection method | Typical reason for selection |
|---|---|---|
| Weld neck | Butt welded to pipe | Controlled bore transition and hub connection |
| Slip-on | Slides over pipe and is fillet welded | Simpler fit-up where approved |
| Blind | Bolted solid closure | Removable line or nozzle closure |
| Threaded | Screws onto threaded pipe | Connection without field welding where permitted |
| Socket weld | Pipe enters socket and is fillet welded | Small-bore forged connection where permitted |
| Lap joint | Loose backing flange with stub end | Bolt-hole rotation and material economy |
| Long weld neck | Extended hub or nozzle connection | Equipment and vessel applications |
Supplier and Inspection Checklist
- Identify the flange standard and required edition.
- State nominal size and class or PN.
- Name the exact flange type.
- Specify facing and gasket system.
- Provide material grade and manufacturing specification.
- State bore, schedule, or connected pipe OD and wall where relevant.
- Confirm drilling, series, tolerances, and custom dimensions.
- Define certificate, NDE, impact, hardness, PMI, and coating.
- Specify bolting and gasket separately.
- Check pressure-temperature suitability and code approval.
Application to Pipe Fittings, Valves, and Flanges
Pipe spools use flanges to connect valves, strainers, pumps, instruments, vessels, and removable sections. Weld-neck and slip-on flanges are welded to pipe, while threaded and socket-weld flanges serve specific applications. Lap-joint flanges work with stub ends, and blind flanges close openings.
Valves may have flanged ends made as part of the body. Their end dimensions must match the mating system, while face-to-face length and body design are controlled separately.
Flanged fittings combine a fitting body with flanged ends. Their available sizes, classes, and materials may differ from individual pipe flanges.
FAQ
What does flange mean in piping?
It is a bolted connection element used to join or close piping components through compatible faces, gasket, and bolting.
What does flanged mean?
It means a pipe component, valve, or nozzle has a flange-type end connection.
What is the most common flange type?
There is no universal answer. Different types serve different design and fabrication needs.
Is Class 150 the same as PN16?
No. They belong to different rating systems and may have different dimensions and pressure-temperature rules.
What is required for a quotation?
Standard, size, class/PN, type, facing, material, bore/schedule, quantity, tests, coating, documents, gasket, and bolting.
Next Steps
Use the flange definition as a specification checklist, not only a product name. Send a drawing whenever bore, facing, drilling, or inspection differs from a catalog item.
Request a Quote
