Derated Flange

[piper1982]

Hi,

What is a derated flange, what are its applications.

Tried googling the topic, but did not get satisfactory results.
Have gone through ASME 16.5, but couldn't find the answer.

Thanks for your help.

 

[LittleInch]

piper1982 - Any more details?

The only thing I can think of is that some flanges are dual rated at low sizes (2" and less) as they are dimensionally the same and hence vendors sell #900 flanges as #600, but may be stamped #900.

Is that what you mean?


My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[davefitz]

The national board NB23 has a discussion on derating components. I think one example would be substituting a lower grade bolt which may imply a lower flange rating.

"Whom the gods would destroy, they first make mad "

 

[donf]

My definition for a derated flange: A rated flange that has been modified so that it no longer meets its original published rating.

One common, but unfortunately not so well known example is drilling and tapping hubless blind flanges to make threaded reducing flanges. B16.5 Table 6 lists the flange size and reduced outlet size combinations that can be made without lowering the flange rating. Exceed those limits and you de-rate the flange.

Another example is machining a conventional B16.5 raised face flange to make an o-ring seal flange. If the o-ring groove encroaches on the minimum flange thickness, then the flange must be derated. (one way to get around this is to start with an ungrooved RTJ (ring type joint) flange.

In either case, calculations would be required to determine the resultant (de-rated) flange rating.

donf

 

[11echo]

I've seen where a used vessel was used in different service and extra nozzles where added for better piping orientation, because the line class was lower the new nozzles were for the lower class. Doing this "derates" all the existing nozzle flanges to the lower class. The vessel documentation was corrected to indicate this after testing, derating all existing nozzles & vessel operation.

 

[piper1982]

Hello Guys,

The question arose, after one of the instrumentation guy came to us (Piping) with a specification in which vendor was providing derated flanges with the package instead of standard flanges.

Thanks for your valuable Feedback.