ASME B16.47 Flanges Guide: Series A vs Series B for Large Diameter Piping

ASME B16.47 is the key standard many engineers use when a project needs large diameter steel flanges beyond the common ASME B16.5 range. It is especially important in oil and gas, petrochemical, power generation, water transmission, marine piping and heavy industrial systems where flange size, weight, bolt pattern and compatibility must be controlled before fabrication.

This guide explains what ASME B16.47 covers, how Series A and Series B differ, and what buyers should confirm before ordering large diameter weld neck or blind flanges for export projects.

What Is ASME B16.47?

ASME B16.47 is a standard for large diameter steel flanges. It is commonly used for NPS 26 through NPS 60 flanges in selected pressure classes. The standard gives dimensional rules for flange outside diameter, thickness, bore, bolt circle, bolt holes, facing, tolerances, materials, marking and pressure-temperature ratings.

In practical purchasing, ASME B16.47 helps ensure that a large flange from one qualified supplier can match the mating flange, gasket and bolting set specified by the project. Without a clear standard and series, large diameter flange orders can become risky because a small difference in drilling or facing may stop site installation.

ASME B16.47 Series A and Series B

The standard includes two dimensional series: Series A and Series B. They cover similar large nominal sizes, but they are not the same flange. Series A is generally heavier and more robust. Series B is generally lighter and more compact. Their bolt patterns, dimensions and weights can differ, so they should not be mixed unless engineering has checked the connection carefully.

A purchase order should always say ASME B16.47 Series A or ASME B16.47 Series B. Writing only “ASME B16.47 flange” is not enough for accurate manufacturing.

Series A vs Series B Comparison Table

Item	ASME B16.47 Series A	ASME B16.47 Series B
General build	Heavier body and stronger design	Lighter and more compact design
Common background	Often associated with MSS SP-44 heritage	Often associated with API 605 heritage
Weight	Usually heavier	Usually lighter
Bolting	Different bolt quantity and pattern from Series B	Different bolt quantity and pattern from Series A
Typical selection	Higher strength, critical service, heavy-duty piping	Existing systems, cost and weight control, suitable lower-risk service
Compatibility	Must mate with Series A dimensions	Must mate with Series B dimensions
Common flange types	Weld neck and blind flanges are common	Weld neck and blind flanges are common; custom needs review

Why Series Selection Matters

ASME B16.47 Series A and Series B flanges may have the same nominal pipe size and pressure class, but their dimensions can still be different. Bolt circle, bolt hole size, number of bolts, flange thickness and weight may not match. If a Series A flange is ordered for a Series B pipeline, the bolt holes may not line up and the gasket may not seat correctly.

This is a costly mistake on large diameter projects because the flange may already be welded, coated, packed or shipped before the mismatch is discovered. Always confirm the series from the drawing, existing flange measurement or project specification before production.

When to Choose Series A

Series A is often selected when the project needs a heavier, stronger flange design. It may be preferred for critical piping, higher mechanical loading, oil and gas transmission, refineries, compressor stations, power generation, high-flow process systems and services where rigidity and long-term reliability matter.

Series A can mean more material weight, higher shipping cost and more demanding handling, but the stronger geometry may be the correct choice when safety and service severity are the main priorities.

When to Choose Series B

Series B is often selected where compact size, lower weight, cost control or compatibility with an existing system is important. It may be found in water pipelines, utility systems, lower-pressure large diameter service and older installations that were designed around Series B dimensions.

Series B should not be chosen only because it is lighter. The project engineer should verify pressure, temperature, external loads, gasket style, mating flange series and bolting before approval.

ASME B16.47 and ASME B16.5

ASME B16.5 is commonly used for smaller metallic pipe flanges up to NPS 24. ASME B16.47 is used for larger diameter steel flanges such as NPS 26 and above within its scope. This size boundary is one of the first things buyers should check when an RFQ includes both standard and large diameter flanges.

If a project uses both ASME B16.5 and ASME B16.47 flanges, keep the standards clearly separated in the flange schedule. Do not assume that pressure class names alone guarantee dimensional compatibility.

Pressure Class and Temperature Rating

ASME B16.47 flanges are class-rated, but a class number is not a single fixed working pressure. The allowable pressure depends on material group and operating temperature. A Class 150 large diameter flange in cold water service is not evaluated the same way as a Class 150 flange in hot chemical or steam service.

For accurate selection, send the design pressure, design temperature, fluid, material grade, flange series and flange type to the supplier. This allows the technical team to check the correct pressure-temperature rating and avoid underspecification.

Common ASME B16.47 Flange Types

The most common ASME B16.47 flange types are weld neck flanges and blind flanges. Weld neck flanges are used where the pipe connection needs strong stress transition and a butt weld. Blind flanges are used to close large pipe ends, pressure openings, vessel nozzles or inspection ports.

Custom large diameter flanges may be possible, but custom designs should be reviewed carefully for bore, face type, thickness, bolt pattern, material, pressure rating and gasket compatibility.

Face Type and Gasket Selection

Large diameter flanges may use raised face, flat face or ring type joint facing depending on project requirements. The gasket must match the face type, pressure class, temperature and fluid. Large gaskets are more sensitive to handling damage, uneven bolt load and surface finish problems.

Before shipment, check that the sealing face is protected. Scratches, dents or coating on the gasket contact area can create leakage during hydrotest or startup.

Material and Manufacturing Checks

Common materials for large diameter steel flanges include carbon steel, low-temperature carbon steel, stainless steel and alloy steel grades. Material selection should follow the design code, corrosion review, temperature requirement and project specification.

Manufacturing may involve forging, rolling, welding, heat treatment, CNC machining, drilling, facing, marking, coating and packing. For critical ASME B16.47 flange orders, buyers should confirm material test certificates, heat numbers, dimensional inspection and any required NDE before shipment.

RFQ Checklist for ASME B16.47 Flanges

A complete request for quotation should include:

• Standard and series: ASME B16.47 Series A or Series B.
• Nominal pipe size and pressure class.
• Flange type, such as weld neck or blind.
• Material grade and certificate requirement.
• Pipe schedule or bore requirement for weld neck flanges.
• Face type, gasket requirement and bolting standard.
• Quantity, coating, packing and destination.
• Inspection requirements, including third-party inspection if needed.

Common Ordering Mistakes

• Ordering ASME B16.47 without specifying Series A or Series B.
• Assuming Series A and Series B bolt holes are interchangeable.
• Using pressure class names without checking temperature derating.
• Forgetting bore or pipe schedule for weld neck flanges.
• Mixing old plant drawings with new project standards without measurement.
• Skipping inspection documents for large diameter export orders.

FAQ About ASME B16.47

What does ASME B16.47 cover?

ASME B16.47 covers large diameter steel flanges, commonly in the NPS 26 to NPS 60 range, including dimensions, pressure-temperature ratings, materials, tolerances, marking and related requirements.

What is the difference between ASME B16.47 Series A and Series B?

Series A is generally heavier and more robust, while Series B is generally lighter and more compact. Their dimensions and bolt patterns differ, so the correct series must be specified before manufacturing.

Can Series A and Series B flanges be connected together?

They should not be mixed unless engineering confirms dimensional compatibility, gasket seating and bolting details. In most orders, the mating flanges should be the same series.

Is ASME B16.47 the same as ASME B16.5?

No. ASME B16.5 is commonly used for smaller metallic flanges up to NPS 24, while ASME B16.47 is used for larger diameter steel flanges within its scope.

Need ASME B16.47 Large Diameter Flanges?

Songhai Flange supplies ASME B16.47 flanges, Series A flanges, Series B flanges, weld neck flanges, blind flanges and custom large diameter flange products for oil and gas, chemical, power, marine, water treatment and OEM projects. Our team can support drawing review, material selection, machining, drilling, inspection and export packing.