Slip on Pipe Flange: Types, Dimensions, Standards, and Selection Guide

A slip on pipe flange fits over the outside of a pipe and is joined to it by welds, commonly at the hub and at the pipe bore. Buyers select one by matching its nominal pipe size, pressure class, material, facing, and governing standard to the piping design. For stainless steel systems, a slip-on flange can be a practical option when the project permits its connection style and the specified pressure-temperature rating is suitable.

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This guide explains flange types, how to read dimensions and standards, where slip-on flanges are commonly considered, and what information to confirm before requesting a quotation. Exact dimensions and ratings must come from the applicable standard and project documents, not from nominal size alone.

Key Takeaways

• A slip-on flange is sized to fit over the specified pipe; its nominal size does not provide every required measurement.
• ASME B16.5 covers flanges in NPS 1/2 through NPS 24, across several pressure classes. Confirm the current project edition and the applicable material and temperature rating.
• Face style, material grade, wall thickness compatibility, weld details, and inspection requirements should be agreed before ordering.
• For stainless steel service, Longrun can review the requested specifications and prepare a quotation based on the buyer’s drawing or data sheet.

Who This Guide Is For

This guide is for piping engineers, project buyers, distributors, and maintenance teams sourcing slip-on pipe flanges. It is especially relevant when comparing stainless steel flange options or preparing an RFQ for a new installation. If a line is governed by a particular piping code, pressure class, or owner specification, use this guide as a purchasing aid rather than a replacement for engineering review.

What Is a Slip On Pipe Flange?

A slip-on flange has a bore that allows the pipe to pass through the flange before welding. The flange is positioned on the pipe, aligned with the intended connection, and welded according to the approved welding procedure and design requirements. The flange then provides a bolted connection to another flange, valve, pump, or item of equipment.

Core Functions and Typical Uses

The flange creates a detachable joint, which can help with equipment installation, inspection, or maintenance when a bolted connection is appropriate. Slip-on designs are used in a range of industrial piping systems, including water, process, utility, and general service lines, subject to the project’s pressure, temperature, fluid, and code requirements. Their suitability should be confirmed for each service rather than assumed from the flange type alone.

Compared with a weld neck flange, a slip-on flange generally has a simpler fit-up arrangement, but the final joint still depends on correct alignment, welding, and inspection. Buyers should not treat the flange as a direct substitute for another type without checking the design basis and applicable piping code.

Types, Materials, and Face Options

Types by Connection and Facing

“Slip-on” describes how the flange fits over the pipe; it does not, by itself, specify the flange face. Common facing options include raised face (RF) and flat face (FF), while other facing arrangements may be available where the applicable standard and project design allow them. The face must match the mating flange and gasket arrangement.

Buyers may also encounter different flange types within the same piping system, such as weld neck, threaded, socket weld, and blind flanges. These serve different connection or closure purposes. Confirm the required type on the drawing or line list instead of selecting by appearance.

Stainless Steel Material Options

Common stainless steel flange material specifications include ASTM A182 grades such as F304, F304L, F316, and F316L, when specified and suitable for the application. The correct grade depends on factors such as corrosion exposure, process conditions, temperature, and the project material specification. Grade names alone do not confirm compliance with a complete procurement requirement.

Check the requested material standard, grade, heat treatment or supplementary requirements, and documentation expectations. If the project requires a particular material certificate or inspection record, state that in the RFQ and confirm availability before placing an order. Do not assume that a product includes a certification or test record unless it is explicitly agreed.

Dimensions and Standards

Flange dimensions are controlled by the applicable standard and size-pressure combination. For many common projects, ASME B16.5 is the referenced flange standard and covers NPS 1/2 through NPS 24. Its pressure classes include Class 150, 300, 400, 600, 900, 1500, and 2500; a class number is not a universal pressure value in psi and must be interpreted with the relevant material and temperature tables.

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A dimensional check typically includes the flange outside diameter, bolt circle diameter, number and size of bolt holes, flange thickness, hub dimensions, bore, and facing details. Pipe nominal size is not the same as the measured outside diameter: for example, NPS 2 pipe has a nominal designation of 2 inches, while its standard outside diameter is 2.375 inches (60.3 mm). Use the specified pipe schedule or wall thickness to verify bore compatibility.

Some larger-diameter applications use other standards, such as ASME B16.47, where applicable to the design. Standards, editions, pressure-temperature ratings, and dimensional requirements should be confirmed against the project specification. If a drawing calls for a non-standard or project-specific dimension, identify it clearly and request technical review before production.

How to Select the Right Slip-On Flange

Step 1: Confirm the Design Basis

Start with the line list, piping class, equipment drawing, or purchase specification. Record the nominal pipe size, material specification, pressure class, facing, and governing standard, including its edition if provided. Also confirm the design pressure and temperature with the responsible engineering team; flange class selection cannot be finalized from pressure alone.

Step 2: Check Pipe and Flange Compatibility

Match the flange bore to the pipe outside diameter and specified wall thickness, then verify the dimensions against the required standard. Confirm that the flange can be positioned and welded as intended, and that the joining details meet the approved design and welding requirements. For stainless steel lines, also check compatibility between the flange material, pipe material, and service environment.

Step 3: Confirm Facing, Gasket, and Bolting

Specify whether the flange is RF, FF, or another approved facing, and confirm that the mating component uses a compatible face. The gasket type, dimensions, and bolting should follow the piping design rather than being inferred from the flange description. If the flange connects to equipment, verify the equipment nozzle dimensions and facing before releasing the order.

Step 4: Review Inspection and Documentation Needs

List any required inspection, marking, traceability, or material documentation in the purchase inquiry. Requirements vary by project, so buyers should distinguish mandatory code or owner requirements from preferences. Agree on the scope and format of documentation before production to reduce clarification delays.

Cost, MOQ, and Lead Time Considerations

Price depends on factors such as size, pressure class, material grade, facing, manufacturing route, order quantity, and required inspection or documentation. Stainless steel grade and flange weight can also affect the quotation, but the impact varies by specification and market conditions. A comparable quote should use the same technical requirements across suppliers.

Minimum order quantity and lead time are supplier- and order-specific; they should be confirmed rather than assumed. Custom dimensions, special material requirements, or additional inspection may affect production planning. For a more accurate quotation, provide the quantity, delivery destination, required date, and complete technical description with the initial inquiry.

Supplier Evaluation Checklist

• Can the supplier quote the specified standard, edition, size, class, material, and facing?
• Will the supplier clarify bore and dimensional compatibility with the stated pipe schedule?
• Are inspection, marking, traceability, and document requirements clearly acknowledged?
• Are quotation validity, MOQ, lead time, packaging, and delivery terms stated?
• Can technical questions be reviewed before production or shipment?

Longrun supplies stainless steel piping products and can review slip-on flange inquiries against the buyer’s stated requirements. For a quotation, send the standard, size, pressure class, material grade, face type, quantity, and any drawing or documentation requirements. Where a detail is unknown, identify it as pending engineering confirmation rather than substituting an assumption.

Conclusion: What Should You Specify?

A slip-on pipe flange is selected by matching its fit over the pipe and its bolted interface to the piping design—not by nominal size alone. Confirm the applicable standard, pressure class and rating basis, material, dimensions, face, gasket arrangement, and welding requirements before purchase. These checks help buyers compare quotations on a consistent technical scope and reduce avoidable specification gaps.

Your next step is to prepare an RFQ with the line or equipment details, quantity, delivery requirements, and documentation expectations. Longrun can use that information to review the request and provide a stainless steel flange quotation for your project.

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