ANSI / ASME B16.5 Flange Dimensions

Flange Standards
The most commonly referred to flange standard in the oil and gas industry is arguably ANSI B16.5 (ANSI - American National Standards Institute). However, despite being referred to extensively by engineers, flange manufacturers and pipe fitting suppliers the ANSI B16.5 standard does not technically exist, rather it its understood as another way to say ASME B16.5.
So what is the difference between the ANSI B16.5 Pipe Flange Standard and the ASME B16.5 Flange Standard? There is no difference.
The B16.5 standard was first published by ANSI in 1973. Though prior to that it was an ASA standard. In 1996 the ANSI standard changed to ASME B16.5. However for 10 years before the change, the pipe flange standard included was listed as ANSI/ASME B16.5.

Other standards for flange dimensions are used, e.g.
- British Imperial flanges BS 10,
- Metric flanges SABS 1123, BS 4504, DIN 2501,
- Japanese and Korean flanges JIS-B-2212, JIS-B-2214 & KS-B-1503


ANSI Flange Pressure Ratings
Pressure rating is defined as the maximum allowed pressure that a flange can withstand at increasing temperatures. According to the ANSI/ASME B16.5 specification, there are seven flange pressure ratings: 150, 300, 400, 600, 900, 1500, and 2500.
The term pressure rating is often referred to as "class" i.e. a class 150 flange. Even this is often abbreviated by the use of either "#", "Lb" or “"Lbs" all of which are pronounced pounds and are interchangeable, i.e. they all refer to the exact same concept of pressure/temperature performance of a flange.
In practice this means that if two flanges have the same bore size (say 8 inches), are made from the same material (say A105), but have different pressure ratings (one flange is class 150, the other 300), the lower rated flange (the 150lb one) will be smaller, lighter, and less robust than the higher rated flange (300lb one).


ANSI B16.5 Flange Dimensions Tables & Charts
The following ANSI flange charts & flange tables provide flange dimensions including, flange overall diameters, number of bolts and bolt size for the most common sizes of ANSI Flanges for ratings from ANSI 150 through to ANSI 1500. They also provide flange bolt circle diameters, also known as pitch circle diameter (PCD) dimensions.


ANSI 150 lbs Flange Dimension Chart
The lowest pressure rating for ANSI flanges is 150 lbs.

ANSI 150# flange dimension chart

ANSI 300 Flange Dimension Chart
The second lowest pressure rating for ANSI flanges is 300 lbs.

ANSI 300# flange dimension table

ANSI 600 Flange Dimension Chart
Pipe flange dimensions table for ANSI 600 lbs rated flanges.

ANSI 600# flange dimension chart

ANSI 900 Flange Dimension Chart
ANSI flange tables for 900 lbs rated weld neck flanges.

ANSI 900# flange dimension table

ANSI 1500 Flange Dimension Chart
ANSI flange tables for 1500 lbs rated weld neck flanges.

ANSI 1500# flange dimension chart

ANSI 2500 Flange Dimension Chart
The highest of the seven pressure rating for ANSI flanges is 2500 lbs. Below is an ANSI flange table for 2500 lbs rated weld neck flanges.

ANSI 2500# flange dimension table



Further Reading - external links

For those who want to delve further into the world of piping, then the following books will be of interest: