Flange selection guide
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.
Rating designations are not direct conversions
ASME Class, PN, JIS rating designations and table-based systems use different definitions and dimensional requirements. Matching or converting a number does not establish physical interchangeability. A Class designation must not be read as an allowable pressure in psi at all temperatures, and PN must not be used as an unrestricted operating-pressure limit.
Use the correct material and temperature basis
Identify the governing standard and edition, then the applicable material and rating requirements for the design temperature. Consider the full design-temperature range and required material condition. No numerical rating table is supplied here: the engineer must use the governing technical documents and project design basis.
Check the complete assembly
The pressure boundary includes the flange pair, pipe or nozzle, gasket, bolting and any interposed component. A higher-rated individual flange does not automatically increase the allowable conditions of the assembly. External loads, thermal cycling, corrosion allowance and other project requirements may require additional design checks.
Keep operating, design and test conditions distinct
Normal operating pressure, design pressure and an inspection or test pressure serve different purposes. A hydrostatic test value is not permission to operate continuously at that pressure. Identify the required test procedure and acceptance criteria separately from the operating and design conditions.
Selection reference only. Offered scope, technical compliance and availability are confirmed against the complete project enquiry.
Dimensions and connection data
Define Flange Pressure Ratings 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 Pressure Ratings with the related forms or references below. A related product is not necessarily a permissible substitute.
| Related product / reference | Distinction | Check before selection |
|---|---|---|
| ASME B16.5 Flanges | An ASME B16.5 enquiry identifies the flange type, nominal size, class, material and facing under the specified edition. The standard name alone does not define a complete joint. | ASME B16.5 edition, flange type, NPS and class |
| ASME B16.47 Flanges | ASME B16.47 covers large-diameter steel flange requirements within its defined scope. Every enquiry must distinguish Series A from Series B. | Explicit Series A or Series B designation |
| EN 1092-1 Flanges | EN 1092-1 flange enquiries use a steel flange type, DN and PN designation together with the exact material and facing requirements. | EN 1092-1 edition, type, DN and PN |
| BS 10 Flanges | BS 10 flange enquiries must state the applicable table as well as the nominal size. A table designation is not interchangeable with an ASME class or a PN label. | BS 10 edition, table and nominal size |
| 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 Pressure Ratings 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 Pressure and Temperature
Specify the complete joint and design conditions. This checklist is not a dimensional table or an engineering approval.
| Item | Requirement |
|---|---|
| Standard | Exact edition and flange/rating designation |
| Material | Specification, grade, condition and applicable rating group |
| Conditions | Design pressure, temperature range and relevant external loads |
| Assembly | Gasket, bolting, mating components and testing requirements |
Continue the specification