ANSI B16.5 Flanges

ANSI B16.5 flanges are the standard American flange pattern. They’re also called ASME B16.5 flanges, or simply ANSI flanges. We hold stainless steel ANSI flanges at 150LB and 300LB, in slip-on, blind, threaded and weld neck forms.

ANSI B16.5 Flanges

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What are ANSI B16.5 flanges?

ASME B16.5 covers pressure-temperature ratings, materials, dimensions, tolerances, marking and testing for pipe flanges and flanged fittings from NPS ½ to NPS 24. “ANSI flanges” is the older and more common name, but the standard itself is published by ASME.

NPS stands for nominal pipe size, which is the American way of sizing pipe. Flanges for pipe larger than NPS 24 are covered by a separate standard, ASME B16.47. Pipe flanges of this kind are used across many industries, including petrochemical processing.

What does LB mean on an ANSI flange?

In our product names, LB stands for the pressure class. So 150LB means Class 150 and 300LB means Class 300. The standard defines seven classes in total, from 150 up to 2500.

The class number isn’t a pressure in psi. A flange’s rating depends on its material and the temperature, so the same class gives different ratings in different grades, such as 304 and 316.

What is the difference between 150LB and 300LB?

A 150LB flange, also called an ANSI 150 flange, has a lower rating than a 300LB flange of the same size. The 300LB flange has different dimensions and bolting, so the two won’t fit together.

150LB is the common choice for general duties, while 300LB is chosen where the pressure or temperature is higher.

Which ANSI B16.5 flange types are available?

Our ANSI range comes in the main flange forms, each with a raised face (RF):

RFWN flanges (raised face weld neck), for demanding pressure and temperature duties

RFSO flanges (raised face slip-on), for economical welded joints

RFBL flanges (raised face blind), for closing off a line

SCRD flanges (screwed or threaded), for joints made without welding

Class 150 lap joint backing flanges are also available in a galvanised finish through our galvanised flanges range.

Should you choose ANSI or EN1092-1?

ANSI B16.5 flanges use NPS sizes and pressure classes, while EN1092-1 flanges use DN sizes and PN ratings. Don’t assume the two are interchangeable, because the drilling usually differs.

Choose the standard your existing pipework follows. If you need a flat-faced option, our reduced thickness flanges are drilled to match both EN1092-1 PN16 and ANSI B16.5 150LB.

What are the common ordering mistakes?

The first is mixing classes. A 150LB flange can’t be joined to a 300LB flange. The second is mixing faces, because raised face and flat face flanges aren’t normally joined to each other. The third is leaving out the grade, so always state 304 or 316.

What should you tell us when you enquire?

To pick the right ANSI B16.5 flange, we need a few details. Please tell us:

1. The NPS size and the class, either 150LB or 300LB, because those two details fix the dimensions and the bolting.

2. The flange type, such as weld neck, slip-on, blind or threaded.

3. Whether you want a raised face.

4. The grade, either 304 or 316.

5. How many you need.

If you’re replacing a flange, read the markings on the old one first, because they usually show the class and size. Send us a photo if you’re not sure what they mean.

Frequently asked questions

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

In practice, yes. The standard itself is published by ASME, but ANSI B16.5 is the older and more common name, so you’ll see both used for the same flanges.

What does 150LB mean on a flange?

LB stands for the pressure class, so 150LB means Class 150. The class number isn’t a pressure in psi, because what a flange can take depends on its material and the temperature.

What pipe sizes does ASME B16.5 cover?

The standard covers pipe flanges and flanged fittings from NPS ½ to NPS 24. Flanges for larger pipe are covered by a separate standard, ASME B16.47.

Can a 150LB flange be joined to a 300LB flange?

No. Class 150 and Class 300 flanges differ in dimensions and bolting, so they won’t fit together. Always match the class of the flange you’re joining.

Are ANSI and EN1092-1 flanges interchangeable?

Don’t assume they are. ANSI B16.5 flanges use NPS sizes and pressure classes, while EN1092-1 flanges use DN sizes and PN ratings, and the drilling differs. Check which standard your pipework follows before you order.

Contact Anglo Stainless for more information

Our ANSI B16.5 flanges come in 304 and 316. Each flange type suits different duties, and the different types of flanges and their uses come down to pressure, temperature and how the joint is made. For advice on your system, please contact us. You can also request our brochure using the form below.