Welded connections
Expander Flanges
An expander flange incorporates a transition between a smaller pipe-side connection and a larger flanged bore. The transition geometry is part of the component design.
Welded connections
Reducing Flanges
A reducing flange combines a larger mating-flange interface with a smaller pipe connection or bore. Both the mating size and the reduced connection must be identified.
The reduction can be incorporated into different flange constructions. A smaller opening in a familiar bolt pattern does not by itself establish pressure suitability or a standard design. Specify the actual hub, bore and pipe-side arrangement, including the transition where one is required.
Compare flange typesTwo sizes, one interface
Identify the larger flange designation separately from the smaller connected pipe size and wall. This avoids confusing a reducing flange with a separate reducer installed next to an ordinary flange.
Confirm the permitted construction
Where ASME B16.5 is specified, confirm the reducing configuration and applicable requirements under the stated edition. Non-standard transitions require their own approved design basis.
Dimensions and connection data
Define Reducing Flanges 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 Reducing Flanges with the related forms or references below. A related product is not necessarily a permissible substitute.
| Related product / reference | Distinction | Check before selection |
|---|---|---|
| Expander Flanges | An expander flange incorporates a transition between a smaller pipe-side connection and a larger flanged bore. The transition geometry is part of the component design. | Pipe-side size and larger flange-side bore |
| 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 |
Inspection, documents and delivery
Define acceptance requirements for Reducing Flanges 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. |
Specification checklist
Define your reducing flanges
Availability, dimensions and pressure-temperature suitability are confirmed against your complete enquiry.
| Item | Requirement |
|---|---|
| Mating size | State flange nominal size, rating and facing |
| Reduced connection | Specify smaller pipe size, schedule and bore |
| Construction | Identify weld neck, slip-on or another required arrangement |
| Transition | Provide hub geometry, end preparation and design basis |
| Material & quantity | Exact material designation, quantity and required certification or inspection documents |
Application context
Where this form is considered
- Connections between differently sized equipment and pipework
- Compact reductions at a flanged interface
- Replacement joints with a specified reduced bore
Related connections
Compare other flange forms
Welded connections
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.
Welded connections
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.