#### 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 – 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 PROOF

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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