Pipe Sch. and Flange Rating

[shahyar]

Is there any formula/Table to understand what is "equivalent"(from max allowable pressure point of view)flange rating of a specific pipe size with specific schedule number?
for example 3" pipe with Sch #XS is equal to (can be connected to) Flange 300 lb?

Thanks for your replies

 

[PAN]

shahyar

I do not see any problem to use 3"-Sch.XS, welding neck flange class 300.

Assume that you use carbon steel pipe, Sch. 40 is also acceptable. The weakest point should be flange connection.

Please give the specific question.

 

[moltenmetal]

Flange rating and pipe schedule aren't tied in the simplistic way you're describing. As PAN says, there are instances where you use 300# flanges on sch10S pipe, and there are also situations where you may need XXS pipe for the same flange rating. If you dumb the design exercise down to something as simple as a table, you end up with massive overdesign for most cases without totally eliminating the possibility of underdesign in other cases.

 

[shahyar]

Thanks.
In my question, I mentioned "Formula",too.(Even before "Table").
If that is not "simplistic", I like to know the way that I finally, can say: "I do not see any problem to use.." , in a specific situation.
Probably here is not good place for the answer, but I am looking for some sources for that type of calculation.

Thanks again.

 

[jte]

shahyar-

I'd say the simplest "formula" is as follows: Design the pipe for a given set of design conditions. Choose a flange which meets the design conditions. Combine pipe and flange.

As mentioned in previous posts, trying to get it all into one formula/table isn't feasible. Think about it: If it was, we'd all be using the formula/table.

Things you'd have to incorporate into your formula include (but, as the lawyers would force me to say, "but are not limited to"):
Design pressure, design temperature (don't forget that flange ratings usually start to drop before allowalbe piping stress), corrosion allowance, piping load on flanges, MDMT, etc.

Its about as simplistic as this mechanical engineer thinks process engineering is!

jt

 

[ytse]

Flange ratings are defined in ASME B16.5 for the different materials at different temperatures (e.g. 150# CS flange -material group 1.1 - has a rating of 285 psi at 100F)

For pipe, it's a different story. It all depends on the piping code you are using to design your system. Different piping codes has different formulas for calculation of pipe wall thickness and different allowable stresses (even for the same material).

For example, ASME B31.3 require that the mil tolerenance be subtracted from the nominal wall thickness when calculating the pressure rating, where B31.4 uses nominal wall thickness for that calculation. Also, B31.3 uses a 0.85 weld joint efficiency factor on welded pipe where B31.4 use a joint efficiency facor of 1 on most ERW pipe. These variations, in addition to the different allowable stress, produce vastly different results among different codes.

You need to determine which code you are using for the piping system first, then look up the fomula in the appropiate code.