A slip on pipe flange fits over the outside of a pipe and is typically secured with fillet welds. To select one, match the flange standard, nominal pipe size, pressure class or rating, material, facing, and bore to the connected piping and service conditions. Dimensions are not interchangeable across standards or ratings, so confirm them against the project specification and the applicable standard before ordering. This guide explains what to check and how to prepare a reliable purchasing request.
This guide is for piping engineers, project buyers, fabricators, and distributors evaluating slip on pipe flanges for a new installation or replacement. It is useful when comparing dimensions, standards, and material options before requesting a quote. It is not a substitute for the project’s piping design documents or the applicable flange standard. Where pressure, temperature, or safety are involved, have the selection reviewed by a qualified engineer.
A slip-on flange has a bore that allows it to slide over the pipe end before welding. In a typical installation, the fabricator positions the flange and makes fillet welds at the pipe-to-flange connection, following the approved welding procedure and applicable construction code. The flange face connects to a matching flange using bolts and a gasket selected for the service. This construction is different from a weld neck flange, which has a tapered hub intended for butt welding to the pipe.
Slip-on flanges are used in many industrial piping systems where their design, rating, and joining method meet the project requirements. They may be considered for utility, process, water, or general service lines, but suitability depends on pressure, temperature, cyclic loading, corrosion exposure, and the governing code. A flange type should not be selected on purchase price or ease of fabrication alone. For severe service or demanding fatigue conditions, the design engineer may specify another flange type.
Flange dimensions depend on the governing standard, nominal pipe size, pressure class or rating, material group, and facing. Key dimensions typically include outside diameter, thickness, bolt-circle diameter, number and size of bolt holes, bore, and facing details. A dimension from one standard or rating should not be assumed to match another, even when both products are described using the same nominal pipe size. Use the standard’s dimensional tables and the project drawing as the controlling references.
ASME B16.5 covers pipe flanges and flanged fittings from NPS 1/2 through NPS 24, across specified pressure classes and materials. ASME B16.47 addresses large-diameter steel flanges from NPS 26 through NPS 60, with Series A and Series B configurations that should not be treated as interchangeable. For stainless steel pipe, ASTM A312 is a commonly specified pipe material specification; it is not a flange dimensional standard. The flange material specification must be stated separately and checked for compatibility with the pipe and service.
Projects may also specify standards such as EN 1092-1, which has its own designations, dimensions, and pressure designation system. Do not convert between standards based only on a nominal size or a pressure label. Confirm the complete standard and edition required by the contract, along with the flange type, facing, and material grade. If the project documents do not clearly identify these details, resolve the discrepancy before procurement.
| Selection item | What to confirm | Why it matters |
|---|---|---|
| Standard and size | For example, ASME B16.5 and the specified NPS | Controls dimensional series and flange configuration |
| Class or rating | Required designation and service conditions | Must be evaluated with material and temperature limits |
| Material | Flange grade and any required material specification | Supports compatibility and documentation review |
| Facing and bore | Facing type, finish requirements, pipe outside diameter, and wall | Supports gasket fit-up and welding preparation |
Identify the governing design code, flange standard and edition, nominal pipe size, class or rating, material, and facing from the line list or piping class. Check whether the project calls for a particular flange type, bore, coating, or end preparation. If the specification uses an abbreviation, confirm its meaning rather than relying on a supplier’s default. This first step prevents a dimensionally similar but noncompliant substitution.
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Verify the pipe outside diameter and wall thickness, then confirm that the flange bore and welding details suit the actual pipe and approved fabrication method. Nominal pipe size is a designation, not a direct measurement of the pipe’s outside diameter. Also check that the flange can be positioned as required and that the joint’s welding and inspection requirements are achievable. Where the line uses a nonstandard pipe dimension or a lining, provide a drawing or additional measurements for review.
Review the process fluid, operating and design temperatures, pressure, corrosion conditions, and any cyclic or vibration loads. Confirm that the flange material, pipe material, gasket, and bolting are compatible under the project’s engineering requirements. Pressure class alone does not establish a safe working pressure for every material and temperature combination. Use the applicable standard tables and design code rather than relying on a generic pressure conversion.
Specify the facing required by the mating flange and gasket arrangement, and confirm bolt-hole details against the same standard and rating. State whether the order requires material test documentation, heat or lot traceability, inspection records, marking, or other project-specific quality documents. These requirements can affect sourcing and should be agreed before the purchase order is placed. Provide the required document format or inspection plan when available.
Carbon steel and stainless steel are common flange material categories, but the correct grade depends on the design specification and service environment. Stainless steel grades should be selected based on the project’s corrosion and temperature requirements, not simply because the connected pipe is stainless. Confirm the exact flange grade and the applicable material specification with the engineer or project documents. Longrun can review the requested stainless steel flange details alongside stainless steel pipe requirements to help identify missing purchasing information.
Pricing and lead time depend on factors such as size, rating, material, standard, quantity, finish, inspection, documentation, and availability. A nonstandard bore or project-specific requirement may need additional review. To obtain a useful quotation, send the full specification, quantity, delivery destination, required date, and any inspection or traceability conditions. Do not assume a quoted delivery estimate includes third-party inspection or documentation unless those items are explicitly confirmed.
A clear quotation should make it possible to compare like-for-like products. Ask the supplier to list any exclusions and deviations rather than leaving them implicit. For critical projects, align inspection and documentation requirements before confirming the order. This gives engineering, procurement, and quality teams a shared basis for review.
The right slip on pipe flange is the one that matches the project’s dimensional standard, size, pressure class or rating, material, facing, bore, and service conditions. Begin with the piping specification, verify pipe fit-up, and confirm applicable design and welding requirements before purchase. Remember that ASME B16.5 covers NPS 1/2 through NPS 24, while ASME B16.47 covers NPS 26 through NPS 60; dimensions and ratings still need to be checked for the exact configuration. For an evaluation or quotation, share your flange standard, size, rating, material, quantity, destination, and documentation requirements with Longrun.
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