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Compatibility between pressure classes and size
API and ASME/ANSI flanges are not necessarily interchangeable, however some of the RTJ styles from ASME B16.5 do match up dimensionally with existing API flanges. API 6A flanges in 5000# class and below are often made from A105 carbon steel with a 45K minimum yield strength, whereas the API 6BX flanges of 10000# class and above require a steel with an even higher yield strength. The most common of those is AISI 4130 with a 75K yield.
You are more likely to find ASME/ANSI flanges in general pipeline assembly work and vessel service, whereas API flanges are often found in oilfield equipment as originally intended. B16.5 flanges will typically deal with materials such as air and high flow liquids, whereas API will handle primarily unrefined crude oil, refined petrochemicals, and high energy gases.
The flanges per standards API 6A and ASME/ANSI B16.5 which share dimensions are listed below:
| Flange | Pressure Class Rating | Nominal Size Range (inches) | ||
|---|---|---|---|---|
| ASME/ANSI B16.5 | API 6A | ASME/ANSI B16.5 | API 6A | |
| Weld neck | 600 | 2000 | 1/2 - 24 | 1 13/16 - 11 |
| Weld neck | 900 | 3000 | 1/2 - 24 | 1 13/16 - 11 |
| Weld neck | 1500 | 5000 | 1/2 - 24 | 1 13/16 - 11 |
| Threaded companion and blind | 600 | 2000 | 1/2 - 24 | 1 13/16 - 21 1/4 |
| Threaded companion and blind | 900 | 3000 | 1/2 - 24 | 1 13/16 - 20 3/4 |
| Threaded companion and blind | 1500 | 5000 | 1/2 - 24 | 1 13/16 - 11 |
Complete inventory of API flanges in all standard sizes, materials, and pressure ratings — from standard ANSI specifications to custom configurations.
When standard products don't fit your application, our engineering team designs and manufactures custom solutions to your exact specifications.
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