ASME B16.47 Flanges: Series A vs. Series B, Sizes, and Selection Guide

ASME B16.47 covers large-diameter steel flanges in nominal pipe sizes (NPS) 26 through 60 inches. It includes two dimensional series: Series A and Series B. They are not interchangeable by default, even when their nominal size and pressure class match, because bolt patterns and other dimensions can differ. To select the right flange, confirm the project’s required series, NPS, pressure class, material, facing, and mating equipment before requesting a quotation.

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This guide is for engineers, contractors, and industrial buyers comparing B16.47 flanges for new pipelines, replacements, or procurement specifications. It explains how the series differ, what size information to check, and how to reduce fit-up and sourcing risks. The applicable edition of the standard and project requirements should always govern final selection.

Key Takeaways

• ASME B16.47 applies to large-diameter steel flanges from NPS 26 through NPS 60.
• Series A and Series B have distinct dimensions; match the series on both sides of a joint.
• Pressure class, material, facing, temperature, and service conditions all matter alongside nominal size.
• Use the project specification and the applicable standard tables to verify dimensions before ordering.

What ASME B16.47 Covers

ASME B16.47 is a dimensional and rating standard for large-diameter steel pipe flanges. Its size range begins at NPS 26 inches and extends to NPS 60 inches. The standard includes several pressure classes, including Class 75, 150, 300, 400, 600, and 900; the available size range can vary by class and series, so check the relevant table rather than assuming every combination is covered.

The standard addresses dimensions and related requirements for covered flange types, including welding neck and blind flanges. A flange’s pressure-temperature rating depends on factors such as its material group and service temperature, not just the class number. For stainless steel applications, verify that the specified grade and product form are permitted by the applicable requirements and compatible with the project’s service conditions.

Series A vs. Series B

Series A and Series B provide different dimensional options within B16.47. Series A is associated with MSS SP-44, while Series B is associated with the former API 605 dimensional system. In many comparable size and class combinations, Series A flanges are heavier and have a larger overall envelope, while Series B designs are generally more compact and may use a different bolt arrangement.

These are general tendencies, not a substitute for checking the standard dimensions. The outside diameter, flange thickness, bolt circle, bolt-hole count, and bolt-hole diameter must be verified for the exact NPS, class, and series. A Series A flange should not be assumed to fit a Series B flange simply because both are marked with the same nominal size and pressure class.

Why the Series Difference Matters

Flange joints depend on alignment between the mating faces and bolt holes. A mismatch in bolt-circle diameter or hole pattern can prevent assembly, while differences in facing or flange dimensions can affect the joint design. For replacements, use the equipment drawings, original flange markings, or verified measurements to establish the series instead of relying on appearance alone.

Sizes, Pressure Classes, and Materials

NPS is a nominal designation rather than a direct measurement of a flange’s outside diameter. A size marked NPS 26 does not mean the flange has a 26-inch outside diameter. Buyers should use the standard’s dimensional tables and the pipe specification to distinguish the nominal size from the flange and pipe dimensions.

B16.47 covers sizes from NPS 26 through NPS 60, equivalent to approximately DN 650 through DN 1500 as nominal metric references. That conversion is for identification and does not replace the inch-based dimensions used in the applicable standard tables. Likewise, a pressure class is not a fixed pressure value in psi for all operating temperatures and materials; confirm the applicable pressure-temperature rating for the specified material group.

Material selection should reflect fluid chemistry, temperature, pressure, corrosion exposure, and applicable construction codes. Carbon steel may suit some services, while stainless steel or other specified alloys may be required for different corrosion or process conditions. Identify the required material grade and governing material specification in the purchase documents, and confirm availability against the selected B16.47 size, class, and series.

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How to Select an ASME B16.47 Flange

1. Confirm the Required Series and Size

Start with the piping isometric, equipment nozzle drawing, or project flange schedule. Record the NPS and whether the connection requires Series A or Series B. For an existing system, confirm markings and mating dimensions before ordering, particularly when documentation is incomplete or the flange is a replacement.

2. Match the Pressure Class to the Design Conditions

Use the project design pressure and temperature, material group, and governing code to confirm the required class. Do not select a class based only on a familiar pressure value or a similar-looking existing flange. Where operating conditions approach a rating limit, ask the responsible engineer to verify the allowable pressure-temperature combination.

3. Specify Flange Type, Facing, and Material

State whether the item is a welding neck or blind flange and identify the required facing, such as raised face or ring-type joint, where applicable. Confirm the facing details against the mating flange and gasket specification. Include the material grade, any supplementary requirements, and the required inspection or documentation in the inquiry.

4. Verify the Complete Joint

Check the bolt circle, number and diameter of bolt holes, flange thickness, outside diameter, bore, and facing dimensions against the relevant standard table. Confirm compatible bolting and gasket details with the joint design. For welding neck flanges, verify the bore and end preparation against the connected pipe and welding requirements.

Common Selection and Purchasing Mistakes

• Ordering by NPS and class alone: These details do not identify the series or all joint dimensions.
• Mixing Series A and Series B: Similar labels do not guarantee matching bolt patterns or face dimensions.
• Assuming class equals operating pressure: Pressure-temperature ratings depend on material and temperature.
• Leaving out facing and material details: An otherwise correct flange may not suit the gasket, service, or mating component.
• Using approximate measurements as the specification: Measurements can help identify an existing flange, but final acceptance should be based on verified requirements and applicable tables.

Pricing, MOQ, and Lead-Time Considerations

Pricing for a large-diameter flange depends on the NPS, series, pressure class, material, flange type, facing, quantity, and any machining or inspection requirements. Special material grades, additional documentation, or nonstandard project requirements can affect the quotation and production plan. Minimum order quantities and lead times are supplier- and specification-dependent, so request confirmation for the exact configuration rather than relying on a general estimate.

To help suppliers quote accurately, provide a complete datasheet or inquiry with the standard and edition, NPS, series, class, material grade, facing, quantity, delivery location, and required documentation. If a flange must mate with existing equipment, include a drawing or verified dimensions. Clarifying these details early can reduce avoidable revisions and fit-up questions.

Supplier Evaluation Checklist

• Can the supplier confirm the requested B16.47 series, NPS, and class?
• Will the quotation state material, flange type, facing, and applicable dimensional requirements?
• Can the supplier confirm the requested quantity, delivery schedule, and shipping basis?
• Are inspection records or material documents available when specified in the purchase order?
• Can the supplier review drawings or clarify mismatches before order confirmation?

At Longrun, we work with industrial buyers on stainless steel pipe, fittings, and flange inquiries. Share the project specification or flange schedule so we can review the requested size, series, class, material, and facing and confirm the available supply options. For replacement work, include mating dimensions or equipment drawings to help identify potential compatibility issues before purchase.

Conclusion: Choose by the Full Specification

The right ASME B16.47 flange is the one that matches the required series, NPS, class, material, facing, and joint dimensions—not simply the one with a matching nominal size. Series A and Series B differ dimensionally, so verify the series on both sides of the connection and consult the applicable standard tables. Before placing an order, confirm pressure-temperature suitability and the requirements of the project’s governing code.

Your next step is to prepare a complete flange schedule or inquiry with the standard edition, size, series, class, material, facing, quantity, and documentation requirements. If you are unsure which series is installed, provide verified measurements or a drawing for review. Longrun can use those details to discuss a suitable supply route and prepare a project-specific quotation.

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