ASME B16.47 vs B16.5 Flanges: Key Differences, Sizes, Classes & Selection Guide

When purchasing steel pipe flanges for an oil and gas project, refinery, power plant, or industrial piping system, ASME B16.5 and ASME B16.47 frequently appear on engineering specifications and purchase orders.

Although both standards define dimensional and pressure-temperature requirements for steel pipe flanges, they are not interchangeable. The most important difference is the nominal pipe size range: ASME B16.5 covers NPS 1/2 through NPS 24, while ASME B16.47 covers large-diameter flanges from NPS 26 through NPS 60.

However, the difference goes beyond flange diameter. Before ordering, consider pressure classes, flange dimensions, bolt patterns, Series A and Series B configurations, material requirements, and project specifications.

ASME B16.5 vs B16.47: Quick Comparison

The size boundary is straightforward: NPS 24 is within B16.5, while NPS 26 starts the B16.47 range. There is therefore no NPS 25 flange size that bridges the two standards.

What Is ASME B16.5?

ASME B16.5, officially titled Pipe Flanges and Flanged Fittings: NPS 1/2 Through NPS 24 Metric/Inch Standard, is one of the most widely used flange standards for industrial piping.

The standard establishes requirements covering areas such as:

• Pressure-temperature ratings
• Flange dimensions
• Materials
• Tolerances
• Bolt holes and bolting dimensions
• Flange facing dimensions
• Marking
• Testing
• Designation of flange openings

The current ASME B16.5 standard covers flanges from NPS 1/2 through NPS 24. It includes Class 150, 300, 400, 600, 900, and 1500 across the main size range, while Class 2500 is covered from NPS 1/2 through NPS 12.

Common B16.5 flange types include:

• Welding Neck Flanges: commonly selected for high-pressure, high-temperature, and demanding process applications.
• Slip-On Flanges: Slip-On flanges are generally easier to install than welding neck designs and are widely used in general industrial piping.
• Blind Flanges: Blind flanges close the end of a piping system, nozzle, or vessel connection and are commonly used where future access or isolation is required.
• Socket Weld Flanges: Commonly used in smaller-diameter piping where the pipe is inserted into the flange socket and welded.
• Threaded Flanges: allow connection without welding and may be selected for specific service conditions where threaded connections are permitted.
• Lap Joint Flanges: are useful where piping systems require frequent dismantling or alignment flexibility.

This makes B16.5 suitable for a broad range of standard industrial piping applications.

What Is ASME B16.47?

ASME B16.47, Titled Large Diameter Steel Flanges: NPS 26 Through NPS 60, was developed specifically for large-diameter steel flanges.

The current B16.47 standard covers:

• NPS 26 through NPS 60
• Pressure-temperature ratings
• Materials
• Dimensions
• Tolerances
• Marking
• Testing
• Large-diameter flange configurations

ASME B16.47 includes Class 75, 150, 300, 400, 600 and 900.

Unlike B16.5, B16.47 also incorporates two flange dimensional configurations:

• Series A
• Series B

This distinction becomes particularly important when purchasing large-diameter flanges because a Series A flange and Series B flange of the same nominal size and pressure class should not simply be assumed to have identical dimensions.

What Should Buyers Check Before Ordering B16.47 Flanges?

Large-diameter flange orders require particularly careful technical confirmation.

Before placing a purchase order, confirm:

1. NPS

For B16.47, confirm the exact size, such as 26″, 30″, 36″, 42″, 48″ or 60″.

2. Series

Specify: Series A or Series B

Do not leave this field blank if the project specification requires one specific series.

3. Pressure Class

Confirm whether the flange is Class 75, 150, 300, 400, 600 or 900.

4. Facing

Specify RF, FF, RTJ or another required facing configuration.

5. Material

For example: ASTM A105N

or the material grade specified by the project.

6. Bore

The bore should correspond to the pipe and welding requirements.

7. Inspection

Large industrial projects may require:

• Material Test Certificate
• PMI
• UT
• Dimensional inspection
• Third-party inspection
• Special testing
• Specific marking requirements

8. Mating Flange

When replacing or matching an existing flange, provide the mating flange standard and dimensional information whenever possible.

This is especially important for large-diameter piping because an incorrect Series A/Series B selection can create an installation problem even when the nominal size and pressure class appear correct.

Why Was ASME B16.47 Developed for Large-Diameter Flanges?

Large-diameter piping creates different engineering and manufacturing challenges from smaller piping.

As flange diameter increases, the flange must accommodate:

• Larger pipe diameters
• Higher bending loads
• Larger bolt circles
• Increased bolt loads
• Greater flange weight
• Different fabrication and installation requirements

For this reason, large-diameter flanges have their own dimensional requirements rather than simply extending the B16.5 tables indefinitely.

For example, a NPS 36 Class 300 flange is not simply a larger version of a NPS 12 Class 300 B16.5 flange. The flange dimensions, bolt arrangement, thickness and other requirements are determined by the applicable B16.47 configuration.

This is one reason why purchasing a large-diameter flange based only on the nominal pipe size and pressure class can result in an incorrect quotation or, worse, an incompatible flange.

ASME B16.5 vs B16.47 Size Range

The easiest way to distinguish the two standards is by nominal pipe size.

ASME B16.5

NPS 1/2 to NPS 24

Examples include:

• 2″ Class 150
• 6″ Class 300
• 12″ Class 600
• 18″ Class 900
• 24″ Class 1500

ASME B16.47

NPS 26 to NPS 60

Examples include:

• 26″ Class 150
• 30″ Class 300
• 36″ Class 300
• 42″ Class 600
• 48″ Class 300
• 60″ Class 150

For large-diameter applications, JS FITTINGS supplies ASME B16.47 Series A and Series B flanges as part of its large-diameter flange range. The company’s published product range covers flange sizes beyond the B16.5 range and includes customized dimensions where required by project specifications.

ASME B16.5 vs B16.47 Pressure Classes

Pressure class is another important difference.

B16.5 Pressure Classes

ASME B16.5 includes:

Class 150, 300, 400, 600, 900, 1500 and 2500

However, these classes do not mean that a Class 300 flange has a universal maximum working pressure of 300 psi.

The actual allowable pressure depends on factors including:

• Material
• Temperature
• Material group
• Applicable pressure-temperature rating table

Therefore, “Class 300” should not be interpreted as “300 psi maximum working pressure.”

This distinction is particularly important when selecting flanges for elevated-temperature oil and gas, steam, refinery and process applications.

B16.47 Pressure Classes

ASME B16.47 includes:

Class 75, 150, 300, 400, 600 and 900

The availability of Class 75 is one feature that distinguishes B16.47 from B16.5. B16.5 does not include Class 75.

At the same time, B16.47 does not extend to the higher Class 1500 and Class 2500 ratings found in B16.5.

What Is the Difference Between B16.47 Series A and Series B?

This is one of the most important questions when buying large-diameter flanges.

ASME B16.47 provides Series A and Series B dimensional configurations.

Historically, the two series developed from different industry flange specifications. In practical procurement terms, the important point is that Series A and Series B can have different flange dimensions and bolt arrangements even when the nominal size and pressure class are the same.

For example, a buyer requesting:

36″ Class 300 ASME B16.47 flange

has not necessarily provided enough information for a manufacturer to quote the correct flange.

The RFQ should identify whether the project requires:

ASME B16.47 Series A

or

ASME B16.47 Series B

The applicable project specification, piping class, mating flange and engineering drawings should be checked before production.

Why does Series A vs Series B matter?

The differences can affect:

• Outside diameter
• Flange thickness
• Bolt circle
• Number of bolt holes
• Bolt hole diameter
• Overall weight
• Mating compatibility

A Series A flange should therefore not be replaced by a Series B flange simply because both carry the same NPS and pressure class.

For stockists and distributors, confirming the series before purchasing can prevent costly dimensional mismatches and replacement orders.

Are ASME B16.5 and B16.47 Flanges Interchangeable?

No. They should not be treated as interchangeable standards.

For sizes covered by B16.5, use the B16.5 dimensional requirements.

For large-diameter sizes covered by B16.47, use the applicable B16.47 requirements and confirm the Series A or Series B configuration.

Which Standard Should You Use for Oil and Gas Piping?

There is no universal answer based only on the industry.

Instead, start with the nominal pipe size and project specification.

For smaller and medium-sized process piping, B16.5 is commonly encountered.

For large-diameter transmission pipelines, water pipelines and other large-bore systems, B16.47 becomes relevant.

Typical applications include:

Oil & Gas

Large-diameter gathering, transmission and process piping may require B16.47 flanges, particularly where pipe sizes exceed NPS 24.

Refineries and Petrochemical Plants

B16.5 is widely used for conventional process piping, while large-bore piping may require B16.47.

Power Generation

Both standards may appear on the same project because different piping systems can use different nominal pipe sizes and pressure classes.

Water Infrastructure

Large-diameter water and utility piping may use large-diameter flange standards depending on the project specification.

Pipeline Projects

Large-diameter pipelines are a common application where B16.47 flanges may be specified.

The final selection should always follow the engineering specification rather than relying solely on general industry practice.

How to Select the Correct ASME Flange

A more complete RFQ should identify at least:

1. Flange standard
2. Nominal pipe size
3. Pressure class
4. Flange type
5. Material grade
6. Facing
7. Bore
8. Schedule or pipe wall thickness
9. Quantity
10. Inspection and certification requirements

ASME B16.47 vs B16.5: Practical Decision Guide

A simple way to approach flange selection is:

NPS 1/2–24?

→ Start with ASME B16.5

NPS 26–60?

→ Start with ASME B16.47

NPS 26–60 and the project specifies B16.47?

→ Confirm Series A or Series B

Need Class 1500 or 2500?

→ Check ASME B16.5, because B16.47 does not cover these pressure classes.

Need Class 75?

→ Check ASME B16.47, where Class 75 is included.

But size and pressure class alone are not enough. Material, temperature, facing, bore, flange type and project specifications must also be confirmed before production.

JS FITTINGS: ASME B16.5 & B16.47 Flange Supplier

JS FITTINGS manufactures and supplies forged steel flanges for international industrial projects, including ASME B16.5 and ASME B16.47 Series A & Series B configurations.

The company’s published flange range includes:

• Welding Neck Flanges
• Slip-On Flanges
• Blind Flanges
• Socket Weld Flanges
• Threaded Flanges
• Lap Joint Flanges
• Orifice Flanges
• Spectacle Blind Flanges
• Custom Forged Flanges

Available materials include carbon steel, stainless steel and alloy steel. The published product range covers sizes from 1/2″ to 80″, with custom dimensions available according to project requirements. JS FITTINGS also states that inspection options include UT, PMI, pressure testing and EN 10204 3.1 MTC.

For distributors, stockists, EPC contractors and industrial buyers looking for ASME B16.5 or ASME B16.47 flanges, the company provides bulk supply and technical quotation support.

View JS FITTINGS Pipe Flanges

FAQ:

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

No. Both standards define requirements for steel pipe flanges, but they serve different size ranges. B16.5 covers NPS 1/2 through NPS 24, while B16.47 covers NPS 26 through NPS 60.

Is a 24-inch flange B16.5 or B16.47?

A NPS 24 flange falls within ASME B16.5.

Is a 26-inch flange B16.5 or B16.47?

A NPS 26 flange falls within ASME B16.47.

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

Series A and Series B are different dimensional configurations for large-diameter B16.47 flanges. Their dimensions and bolt arrangements can differ, so the required series should be confirmed before ordering.

Does B16.5 include Class 2500?

Yes. ASME B16.5 includes Class 2500 flanges from NPS 1/2 through NPS 12.

Does B16.47 include Class 1500?

No. B16.47 covers Class 75, 150, 300, 400, 600 and 900.

Does Class 300 mean 300 psi?

No. ASME pressure classes are not direct maximum-pressure values. The allowable pressure depends on material and temperature and must be determined from the applicable pressure-temperature rating requirements.

Can I replace a B16.47 Series A flange with Series B?

Not without checking the project specification and mating dimensions. Series A and Series B can have different dimensions and bolt configurations.

Final Takeaway

The difference between ASME B16.5 and ASME B16.47 flanges is primarily driven by size, but professional flange selection requires more than checking the nominal diameter.

ASME B16.5 is used for NPS 1/2 through NPS 24 and includes higher pressure classes up to Class 2500.

ASME B16.47 is designed for large-diameter flanges from NPS 26 through NPS 60 and includes Series A and Series B configurations, with pressure classes from 75 through 900.

For a correct quotation and a reliable installation, always confirm the complete specification:

Standard + NPS + Class + Series (if applicable) + Flange Type + Material + Facing + Bore + Inspection Requirements.

For international buyers, stockists and EPC contractors, providing these details at the RFQ stage can significantly reduce dimensional errors, quotation delays and compatibility problems.

If you are sourcing ASME B16.5 or B16.47 forged steel flanges, JS FITTINGS can provide carbon steel, stainless steel and alloy steel options according to project specifications.

Request a Technical Flange Quote from JS FITTINGS

Email: admin@jsfittings.com

WhatsApp: +86 180 0311 9682