Blind flange Calculations??

[67prostreet]

hello, i am trying to calculate some blind flange thicknesses but when i compare my values to those being used in B16.48, some thicknesses are off whereas others match up. I am currently using a yield strength of 38,000, gasket diameters from B16.20 & B16.21 and the equation:
t= d_g*(3P/16SEW)^.5 + c. Do you know what values are being used for the quality factor E? Also, should i only be using 90% of my yield strength? I am also using 0.05" for my corrosion allowance. Thanks in advance.

 

[gr2vessels]

Hi 67prosteet,
The formula you mention is correct as per B31.3, clause 304.5.3, formula (15).
The S value is selected from Table A-1 of B31.3 (not 90% of yield) and the E is selected from Table A-1A or A-1B (page 190, 191 of B31.3). Use the corrosion allowance as directed by your customer or use a value confirmed by a competent engineer, in accordance with the process requirements. In corrosive environment, the corrosion allowance would be most likely 1/8", not 0.05".
cheers,
gr2vessels

 

[DSB123]

67prostreet,
Remember that for a blind flange you must also check out the thickness required for the edge bending moment caused by the bolt loading not just use the equation you quote.

 

[67prostreet]

Edge bending, i had never thought of that. Sorry for my inexperience, but where would i find an equation for that (what code book)? This is just frustrating me because some thickness that i calculate match up perfectly with B16.48, but then there are some thickness in random spots that are off by an 1/8" or 1/16" and im not sure why. Anyways, thanks a lot for the help so far. If i could get the code book that would talk about edge bending moments on the flange, i would really appreciate that.

 

[KevinNZ]

I use BS5500 but I think there are equations in ASME VIII.

Why not just use the standard thickness from the flange code?

When I calculate the the thickness of flanges using pressure vessel code rules I always get thicker flnages than the flange codes but using less bolts/studs can get the thinkness down.