Calculating tensile and yeild strength for flanges

[flangeman]

I have some 300# elbows with flanges undersized from the 0.75 inch thickness specified in the ASME B16.5 spec. Is there a formula or other ASME spec that I could use to calculate the reduction in strength verses a 0.62 inch thick flange?

When flanges deteriorate how do you determine when to thin to use?

I am worried about flange shearing and breaking at bolted connection to the pipe.

 

[JohnBreen]

flangeman

Perhaps the best thing to do is to consider the flanges as a "new designs" and analyse them using the Taylor-Bonny Forge Bulletin 502 for flange design (an old classic). The bulletin has forms that you can copy that take you through the design logic and it includes all the information that you need to do the calculations (you will have to go to the ASME B&PV Code to get up-to-date allowable stress values).

There is also a spreadsheet kicking around for automating TB-502. I hate to say this, but I have a pdf file of the bulletin and a copy of the spreadsheet but I have no way of getting them to you. I have been through this before and I know that 10,000 piping engineers have lost their copy of TB-502 and regretably I do not have time to get involved with distribution all over again. But I found both on the Internet so maybe you can too.

Regards, John.

 

[ytse]

ASME B31.3 paragraph 304.5.1 states:

"(a) Flances not in accordance with para. 303 or 304.5.1(b) or (c) shall be qualified as required by para. 304.7.2.

(b) A flange may be designed in accordance with the Boiler and Pressure Vessel Code, Section VIII Division 1, Appendix 2, using the allowable stresses and temperature limits of the B31.3 Code..."

Since you flange is thinner than the B16.5 flange, it should be considered as special design and the simplest is to us the BPV Section VIII, Div 1, Appendix 2 formulas.

 

[JohnBreen]

...........and if you do use the ASMR B&PV Code technique do not be surprised if you calculations indicate that the flanges do not comply. If fact, if you evaluste a new B16.5 flange pair (all dimensions per B16.5) used within the flanges' B16.5 pressure-temperature rating, do not be surprised if the flanges do not comply with the ASME B&PV Code - even if there are zero forces and moments acting on the flange pair.

There is a very interesting Oak Ridge report by Ev Rodabaugh and Sam Moore (Circa 1974) that focused on this paradox.

Regards, John.