Mechanical connections
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.
Mechanical connections
Loose Flanges
A loose flange is a separate backing component working with a collar, lapped end or stub end. It transfers bolt load while the companion component forms the pipe-side seating interface.
The term covers more than one backing-ring construction and may overlap with lap-joint terminology. Confirm the collar standard, contact geometry and assembly clearance. A loose ring alone does not define the wetted material, gasket surface or pressure capacity of the joint.
Compare flange typesRelationship to lap joint
A lap-joint assembly is one familiar use of a separate backing flange. This page addresses the backing component itself, including drawing-specified collars; it does not imply that every loose ring fits every stub end.
Specify both components
Check collar diameter and thickness, contact radius, ring bore and the mating bolt pattern. Identify the process-wetted material separately from the backing component material.
Dimensions and connection data
Define Loose 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 Loose Flanges with the related forms or references below. A related product is not necessarily a permissible substitute.
| Related product / reference | Distinction | Check before selection |
|---|---|---|
| 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 |
| Plate Flanges | A plate flange is a ring-shaped component made from plate, with an open bore and a bolt pattern specified for the mating connection. Plate construction is distinct from a flat gasket facing. | State the plate specification, grade and thickness |
| 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 |
Inspection, documents and delivery
Define acceptance requirements for Loose 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 loose flanges
Availability, dimensions and pressure-temperature suitability are confirmed against your complete enquiry.
| Item | Requirement |
|---|---|
| Companion component | Collar or stub-end designation and drawing |
| Contact geometry | Lap thickness, corner radius, bore and bearing diameter |
| Material split | Backing ring and process-wetted component grades |
| Joint basis | Applicable assembly standard, rating and gasket arrangement |
| Material & quantity | Exact material designation, quantity and required certification or inspection documents |
Application context
Where this form is considered
- Collar-backed piping joints
- Assemblies requiring bolt-hole alignment
- Replacement backing rings for identified stub ends
Related connections
Compare other flange forms
Construction & special designs
Plate Flanges
A plate flange is a ring-shaped component made from plate, with an open bore and a bolt pattern specified for the mating connection. Plate construction is distinct from a flat gasket facing.
Mechanical connections
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.