Allowable pressure for flanges

[DVNMech]

The pressures that are indicated in the pressure/temperature tables for flanges, are these
the maximum allowable pressures at that temperature taken into account internal pressure and external bending moments+axial forces, or do they give the maximum internal pressure for the flange at a certain temperature?
I ask this because some flex. calculation programs use the nominal pressure of a flange to determine if a detailed calculation is necessary. But at higher temperatures, the allowable pressure is of course lower than the nominal value.
How to use these tables? Should the external influences be taken into account? (at higher temperatures)

 

[waskillywabbit]

In my old Taylor Forge book I've always taken them as strictly pressure-temperature ratings as there are no notations or footnotes that they are anything otherwise.

Brian

http://www.mcabeeconstruction.com

Opinions expressed are my own and are not those of the company.

 

[JStephen]

I was just looking in AWWA C207 this morning, and it specifically states that the flange ratings are pressure only, no allowance for externally applied bending or other forces. I assume this would be similar in other flange standards.

 

[Cockroach]

Yes, these are the maximum operating pressures given for a specific temperature range.

For example, ANSI Class 600 is 1440 psig for thermal range not greater than 100F. These flanges are hydrostatically tested to 50% ABOVE MOP, also known as maximum test pressure or MTP. In this case you would need to hydrostatically pressurize to 2160 psig and hold that pressure for 15 minutes or so in order to comply to the piping code.

Going to higher temperatures requires the steel to be derated, thus lowering your MOPs. In this case, the relavent code such as Boiler Branch or CSA Z245.15 should be consulted.

Here in Canada we also use a cold weather engineering specification and demand notch toughness since -40F temperatures can induce crack propagation from surface defects such as notches or pits. This is not part of our discussion, I just wanted to point out the thermal range is not necessarily restricted to INCREASING levels.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada