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Flow Measurement Instrumentation Design

Why Orifice Flow Meter Flange is not Recommended 150# Rating ?

This question comes to mind ? As to Restriction Orifice can have 150# but Orifice flange (Flow meter) is not recommended to have 150# rating.

Orifice Flange Rating

Orifice Flange Rating – 150#

We have the answer in one sentence.

It is due to flange integrity !

It means in simple words :- Orifice that are flange tapped have reduced strength

Due to this drilling in between them their pressure-temperature retaining capacity reduces

So to ensure flanges have Strength to withstand Design pressure and temperature a higher rating than 150# i.e 300# is used .

Now There has to be some proof supporting It !!!


The standard we use for Normal flanges below 24” is ASME B16.5

But for Orifice, the flange standard is ASME B16.36

This standard starts with 300# Flange rating.

In restriction Orifice as there are no tapping hence we go with ASME B16.5 flanges which Start with 150# Rating .

As always ! Thanks a lot for Reading !!

PS :- It is observed that for very large line sizes ( Depends few say above 10”, few say above 20”) 150# can be used as these flanges are stronger at higher line sizes but I have not found concrete proof in standards yet.

I would be very grateful if somebody knows the standard that has this documented.

Author : Asad Shaikh

Profile : Linkedin

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Why Orifice Flow Meter Flange is not Recommended 150# Rating ?

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