instrument flange rating 2

[akbari1358]

Deat all,
I need an advice.
In all equipment mechanical data sheets that i have seen the rating of instrument flanges is one level higher than other flamges. Is there any regulation or mandate for this?

 

[curtis2004]

Can you show us, at least one data sheet? You can black out confidential information like, company name, location, manufacturer, names and initials...

 

[KevinNZ]

You maybe looking at a class 900 system specification. In a class 900 system all small flanges are class 1500. All class 900 small flanges are the same size as class 1500.

 

[MickMc]

Are all your equipment data sheets rated to Class 150 as I have seen some operators specify a minimum Class 300 on instrument connections for mechanical strength?

 

[racookpe1978]

If the instrument has any significant mass on the flange, then the mechanical strength may be desired as a "precaution" against future intr. weight/moment increases without elaborate calc's or rebuilding.

 

[pennpiper]

akbari1358,
We need more information.


Sometimes its possible to do all the right things and still get bad results

 

[moltenmetal]

No, there is no regulation, mandate or even a justification for doing this. But some COMPANY specifications may standardize on a certain minimum flange class merely to minimize their spare parts inventory.

I thought you were asking about the pressure rating of a 2-bolt "instrument flange" of the sort used on a pressure transmitter....

 

[akbari1358]

Dear all, Thanks
The equipment data sheets rated to Class 150 and consultant considered a philosophy as minimum Class 300 on instrument connections for mechanical strength.

 

[jte]

There is a simple reason that some companies mandate instrument connections to have a higher rating: Material properties vary. I'll say simply that "I'm familiar with" a situation in which much time and energy were expended by a project team which had ordered vessel flanges of appropriate rating for the CS or low alloy material. But the pressure was approaching the B16.5 rating limit. Now, the instrument engineers ordered instrumentation such as thermowells with flange ratings to match. In stainless material.

Oops! Now the flange rating of the instruments does not meet the pressure rating of the vessels (and piping). Now refer to ASME B16.5 paragraph 2.3.2. We have a problem.

Far easier to pay a bit more for more robust flanges than to risk project delays and substantial high level engineering involvement by all parties.

 

[donf]

jte,

I am also familiar with the exact situation you described. Certain flanged piping "specialties" are not commercially available in the "stronger" materials of construction.

donf

 

[moltenmetal]

And here, in a nutshell, is what happens when you set pipe specs limited by flange class. A very good lesson indeed.

Another solution, which might be more practical than jumping up a flange class for every flanged instrument connection, would be to put the stainless steel instrument flanges into the carbon steel pipe spec and thereby limit the MAWP to something more practical.

 

[XL83NL]

Also another example why per default (some) specs become over conservative, when such matters aren't reviewed on a case by case basis.