A pipe flange connects piping components; a flange bearing supports or helps locate a rotating shaft. They can both appear on a pump skid or an industrial machine, but they serve different interfaces and must be specified separately.
That distinction matters when a purchasing team receives a bill of materials with the word flange on several lines. Ordering by name alone can leave the supplier guessing: is the item a pressure-joint component, a shaft-support unit or a bearing with an outer-ring flange?
This guide explains how to identify each part, compare the dimensions that matter and prepare a clearer request for quotation (RFQ).
Key takeaways
- A pipe flange is selected for a piping connection; a flange bearing is selected for a shaft and its operating conditions.
- Pipe flange size, pressure class, material and facing must be checked together against the applicable standard and design conditions.
- A bearing unit needs its own shaft size, housing dimensions, mounting pattern, load, speed and operating-environment details.
- A four-bolt housing is not automatically the right bearing merely because it has more mounting bolts.
Pipe flange vs flange bearing: the practical difference
| Question | Pipe flange | Flange bearing |
|---|---|---|
| What does it do? | Connects or closes piping components | Supports or helps locate a shaft |
| What does it connect to? | A compatible mating flange or equipment connection | A support surface or housing bore, depending on the bearing type |
| What is the main design concern? | Joint integrity at the specified pressure, temperature and service | Suitable shaft support for load, speed, alignment and service conditions |
| What dimensions identify it? | Nominal pipe size, flange standard, pressure class, facing and bolt pattern | Shaft or bearing bore size, housing dimensions and mounting pattern, as applicable |
| What else should an RFQ include? | Material, pipe wall or bore where applicable, gasket and inspection requirements | Bearing type or part number, load, speed, seals, locking method and lubrication requirements |
A useful first check: if the component must join a pipe to a valve or nozzle, start with the piping drawing. If it must support a shaft, start with the equipment and bearing drawings. Neither the hole count nor the word “flange” alone identifies the part.
What does a pipe flange do?
A pipe flange is part of a detachable connection between piping components. A typical flanged joint uses two compatible flanges, a gasket and bolting. The flange is only one part of the joint: mating surfaces, gasket, fasteners, assembly and operating conditions all matter.
Common types include weld neck, slip-on, blind, socket weld, threaded and lap joint flanges. The correct type depends on the piping design, the specified standard and the intended connection. For example, a weld neck flange is joined to a pipe by a butt weld, while a blind flange closes an opening.
YANTAIPIPE’s steel pipe flange range includes these product types. For a project requiring a specific connection, the weld neck flange and slip-on flange pages offer starting points for an enquiry.
Five pipe flange details that need to match
- Standard and size. Identify the applicable standard and nominal pipe size (NPS or DN, as specified). Do not assume that similarly labelled flanges from different standards will mate.
- Pressure class and temperature. Give the design pressure and temperature, as well as the specified class. The permitted pressure depends on the standard, material and temperature; “Class 150” does not mean a fixed rating of 150 psi at every temperature.
- Material and service. Specify the material grade and any project requirements for corrosion, low temperature or testing. A grade should be confirmed against the actual service and specification.
- Facing, gasket and bolting. Confirm the required facing and the mating equipment details. Raised face, flat face and ring-type joint arrangements are not interchangeable just because the nominal size is the same.
- Connection and bore. State the flange type and, where relevant, the pipe outside diameter and wall thickness or schedule so the supplier can confirm the bore and weld preparation. Include drawings for non-standard requirements.
For example, ASME describes B16.5 as covering pressure-temperature ratings, materials, dimensions and other requirements for the flanges and fittings within its scope. Its size and class provisions have limits: do not assume every class covers the same size range. Use the edition specified by the project.
What are flange bearings?
Flange bearings support or help locate a shaft, but the term describes more than one product family. Before comparing dimensions, identify which type the equipment actually uses:
- Flange-mounted bearing unit: A bearing insert sits in a flanged housing. The housing is bolted to a support surface; the shaft passes through the bearing.
- Flanged ball bearing: A flange on the bearing’s outer ring helps locate it in a housing bore. It is not necessarily a bolted bearing housing.
- Flanged sleeve bearing: A sleeve-style bearing with a flange, selected for a suitable sliding or oscillating duty according to the manufacturer’s specifications.
On the same skid, steel pipe flanges form part of the bolted piping joints, while flange-mounted bearing units support shafts at equipment mounting surfaces. A flanged ball bearing is instead located in a housing bore, so its mounting details differ. Shandong TFL Bearing Co., Ltd. explains these flange bearings, the three product families and selection considerations for two-bolt and four-bolt units.
The distinction helps when a drawing calls for a “flange bearing”: a shaft bore measurement alone will not tell the supplier whether the item is a complete mounted unit, an individual ball bearing or a sleeve.
How do flange mounted bearings attach to equipment?
Flange mounted bearings generally use a housing with mounting holes to fasten the unit to a supporting surface. The shaft passes through the bearing insert. Housing shape, mounting dimensions, shaft-locking arrangement and sealing vary by product series.
The housing and the supporting surface work together. Before ordering, check the mounting surface’s condition and strength, the shaft position, the available clearance for installation and maintenance, and the equipment manufacturer’s alignment requirements. Consider whether the selected bearing arrangement accommodates the shaft movement expected by the equipment designer; do not assume every unit can be used as either a fixed or a floating bearing.
SKF’s UC range of mounted ball bearing units illustrates the mounted-unit category. Use the selected manufacturer’s catalogue and installation instructions for the actual unit rather than transferring limits from a different series. Use the selected manufacturer’s catalogue and installation instructions for the actual unit rather than transferring limits from a different series.
Two-bolt vs 4 bolt flange bearing: what should buyers check?
A two-bolt housing uses two mounting points; a 4 bolt flange bearing uses four. The choice starts with the machine’s specified interface and operating requirements, not a general rule that one always carries more load.
Compare these details against the equipment drawing and the manufacturer’s data:
- Mounting pattern: Number of holes, centre-to-centre spacing, hole dimensions and housing orientation.
- Shaft interface: Shaft diameter and units, bearing bore, locking method and any shaft-tolerance requirements.
- Duty: Radial and axial loads, operating speed, duty cycle and any relevant vibration or shock.
- Environment: Temperature, dust, washdown, moisture or chemicals, as applicable to the equipment.
- Maintenance: Seal type, lubrication method, access for inspection and any replacement requirements.
The bearing’s published ratings, housing design, bolt specification, support structure and installation all need to be considered. If a machine already uses one housing style, changing to another may require a revised mounting plate or engineering approval.
Example: separate the RFQs for one pump package
The following is an illustrative purchasing example, not an installed design or a recommendation for a specific service. Assume a project team needs a flanged piping connection and a shaft-support unit for the same equipment package.
| Line | Information available | Still needed before a responsible quotation or selection |
|---|---|---|
| Piping item | NPS 4 weld neck flange; ASME B16.5; Class 150; raised face; ASTM A105 material requested | Pipe wall or schedule and bore, design pressure and temperature, mating flange/nozzle details, gasket and bolting requirements, quantity, required edition and inspection documents |
| Bearing item | A four-bolt flanged bearing unit is shown on the equipment drawing | Shaft diameter and units, exact mounting dimensions or part number, load, speed, environment, locking and sealing requirements, lubrication and quantity |
The piping line identifies a starting specification, not proof that the flange is suitable for the service. The bearing line identifies a housing style, not a complete bearing selection. Send each supplier the relevant drawing and obtain engineering confirmation before procurement or substitution.
Copyable RFQ checklist
For a pipe flange RFQ, provide:
- Product type, quantity, standard and required edition.
- NPS or DN, pressure class, facing and material grade.
- Pipe wall thickness or schedule and bore where relevant.
- Design pressure, design temperature, fluid and applicable project requirements.
- Mating connection, gasket and bolting details if required by the order.
- Drawings, inspection requirements, material test certificates and delivery destination.
For flanged bearing units, provide:
- Bearing family, existing part number or drawing, and quantity.
- Shaft diameter and units; mounting-hole pattern and housing dimensions.
- Radial and axial load, speed, duty cycle and environment, if known.
- Locking, sealing and lubrication requirements.
- Whether the item is a complete housing-and-insert unit or an individual replacement bearing.
If any operating value is unknown, mark it to be confirmed rather than choosing a catalogue value by assumption. The supplier can then identify the information needed for selection.
Frequently asked questions
Are pipe flanges and flange bearings interchangeable?
No. A pipe flange is used in a piping connection; a flange bearing is used with a shaft. Similar names or bolt holes do not make their dimensions, loads or functions interchangeable.
Is a four-bolt flange bearing always stronger than a two-bolt unit?
Not automatically. Compare the specific bearing and housing ratings, bolt arrangement, load direction, support structure and installation requirements. A four-bolt housing must also fit the machine’s mounting interface.
Does Class 150 mean a flange can always handle 150 psi?
No. Class is a pressure-rating designation; the allowable pressure depends on the applicable standard, material and temperature. Check the project’s design conditions against the relevant standard and manufacturer documentation.
Can I identify a bearing unit from the shaft size alone?
No. Shaft size is a starting point. The bearing family, housing and bolt pattern, load, speed, seals and locking method also matter. An existing part number and a clear drawing are useful when requesting a replacement.
Do flanged ball bearings always have bolted housings?
No. A flanged ball bearing can have a locating flange on its outer ring and fit into a housing bore. That differs from a flange-mounted bearing unit whose separate housing is bolted to a surface.
Plan the interfaces before ordering
For a combined equipment package, list the piping joint and shaft-support unit separately. Confirm each interface with the responsible engineer, then send each supplier the dimensions and operating conditions relevant to its product.
For piping components, YANTAIPIPE can review your flange type, standard, material and project RFQ. Learn more about YANTAIPIPE or contact the team with your specifications. For bearing selection, consult the bearing manufacturer with the shaft and housing details. Clear information at the enquiry stage makes it easier to identify missing specifications before an order is placed.