Flange selection guide
Flange Types Guide
Start with the pipe or equipment connection, then choose a flange form that fits the design and maintenance requirements. A flange name does not select its material or rating.
Welded connection forms
A weld neck transfers the pipe connection through a tapered hub to a butt weld. A slip-on form fits over the pipe and uses the specified fillet-weld arrangement. A socket-weld form receives the pipe in a recessed socket. These constructions require different bore, pipe-wall and weld details; they are not interchangeable simply because the bolted faces match.
Mechanical and backing arrangements
Threaded flanges connect to a compatible pipe thread, which must be identified by its standard and size. A lap-joint backing flange works with a separate stub end and can rotate for bolt alignment before tightening. Companion describes a flange selected to mate with another connection; it does not identify one universal pipe-side construction.
Closures, measurement and equipment nozzles
A blind flange closes a bolted opening. Operational line blanks instead fit within an appropriate joint arrangement. Orifice flanges include the specified pressure-tapping connections for a coordinated metering assembly. Long weld-neck and equipment-specific connections need the actual nozzle projection, bore and fabrication drawing.
Complete the joint specification
After choosing the connection form, confirm the material, dimensional standard, facing, gasket, pressure-temperature design basis and inspection requirements. Compatibility must be checked at both the pipe connection and the mating flange. Use an approved drawing for any feature outside the selected standard.
Selection reference only. Offered scope, technical compliance and availability are confirmed against the complete project enquiry.
Dimensions and connection data
Define Flange Types Guide as part of the complete joint. These fields identify required engineering data; they are not universal dimensions or a declaration of available sizes.
| Parameter / designation | Technical information | Selection requirement |
|---|---|---|
| Nominal size and bore | State the nominal connection size separately from the actual bore or pipe outside diameter. | A matching size label does not establish matching internal geometry. |
| Outside diameter and thickness | Identify the finished flange diameter, minimum thickness and any hub or collar projection. | Include the drawing datum and units for replacement measurements. |
| Bolt circle and holes | Record pitch-circle diameter, hole quantity, hole diameter and any special orientation. | Check against the mating flange; do not infer a bolt pattern from pressure class alone. |
| Gasket-contact surfaces | Specify face form, seating dimensions and surface finish on the assembled joint. | Include gasket designation; a visually similar surface is not evidence of compatibility. |
| Pipe-side interface | Identify weld preparation, socket, thread, collar or other attachment geometry as applicable. | Provide pipe schedule/wall thickness and the connection-specific standard. |
| Design conditions | State design pressure, minimum/maximum temperature, fluid and mechanical loads. | Pressure class is not a pressure value in bar or psi. Use the material-specific rating basis. |
Compare related options
Compare Flange Types Guide with the related forms or references below. A related product is not necessarily a permissible substitute.
| Related product / reference | Distinction | Check before selection |
|---|---|---|
| Weld Neck Flanges | A tapered hub carries the connection from the flange body to a butt-welded pipe end. The pipe bore and wall thickness are important parts of the flange specification. | Butt-weld end; specify pipe schedule and bore |
| Slip-On Flanges | The flange bore slips over the pipe before the connection is secured with fillet welds. Pipe outside diameter and installation clearance govern the fit. | Slip-over bore with project-specified fillet welds |
| Socket Weld Flanges | A recessed socket receives the pipe end, with a fillet weld at the outside of the hub. Socket depth, bore and assembly requirements distinguish it from a slip-on connection. | Specify socket dimensions and pipe schedule |
| Threaded Flanges | Internal threads connect the flange to a matching threaded pipe end. The thread form, nominal size and mating pipe specification must be stated together. | Specify thread standard, size and engagement |
| Lap Joint Flanges | A backing flange works with a separate stub end or lapped pipe end. The stub end provides the gasket seating surface while the backing flange transmits the bolt load. | Specify flange and stub end as separate components |
| Blind Flanges | A solid flange closes a flanged opening without a through bore. Its bolted connection allows the closure to be removed for access when the system is safely isolated. | Solid centre; identify any required drilling separately |
| Orifice Flanges | Pressure-tapping connections distinguish an orifice flange from a general pipe flange. A matched assembly supports the differential-pressure measurement arrangement around an orifice plate. | Specify the matched flange pair and plate arrangement |
| Long Weld Neck Flanges | An extended neck combines a flanged connection with a longer nozzle section. Neck length, bore and end preparation must be specified for the intended equipment connection. | Provide required projection, wall and bore |
| Companion Flanges | A companion flange is selected to mate with a particular flanged connection. The term describes its role in an assembly, so the actual connection form and dimensions must be identified. | Provide equipment drawing or flange designation |
| Flange Pressure Ratings | A flange class, PN designation or table is not a universal allowable pressure. The design must use the specified standard, material and temperature together. | Exact edition and flange/rating designation |
| Flange Material Selection | Choose a flange material from the service and fabrication requirements, then define the exact grade and product specification. A photograph or broad alloy family cannot establish suitability. | Fluid chemistry, temperatures, pressure and external exposure |
Inspection, documents and delivery
Define acceptance requirements for Flange Types Guide in the purchase order. Required examinations and documents depend on the material, design and project specification.
| Review stage | Information to confirm | Order requirement |
|---|---|---|
| Material identity and traceability | Specification, grade, heat/lot identification and the required material certificate. | Agree documentation and marking before manufacture; visual appearance cannot verify alloy identity. |
| Dimensional verification | Critical dimensions from the selected standard or controlled drawing. | Identify inspection points, tolerances, units and drawing revision. |
| Surface and end condition | Gasket-contact surface, attachment end, edges and any coating exclusions. | State finish and visual acceptance criteria; agree protection of machined surfaces. |
| Supplementary examinations | Any specified PMI, NDE, hardness, impact, corrosion or other tests. | Define the method, sampling and acceptance criteria; tests are not automatically included. |
| Assembly compatibility | Adjoining components, weld or mechanical interface and project service conditions. | Design approval and correct assembly remain separate from a dimensional inspection report. |
| Packing and order release | Quantity, identification, surface protection, documents and delivery destination. | Agree preservation, packaging and release requirements with the order. |
Enquiry checklist
Details for Flange Type Selection
Specify the complete joint and design conditions. This checklist is not a dimensional table or an engineering approval.
| Item | Requirement |
|---|---|
| Pipe interface | Butt weld, slip-on, socket weld, thread or stub-end arrangement |
| Mating face | Facing type, gasket seat and bolt pattern |
| Design | Material, pressure-temperature conditions and external loads |
| Project | Access, inspection, maintenance and drawing requirements |
Continue the specification