Calculating blind flange min. thickness 1

[BRT549]

I'm trying to figure out the minumum thickness of a 36" blind flange. I'm making a crud trap with some big HDPE pipe, and am going to use 2 blind flanges on the ends. I found a formula in Perry's:

t = d(3P/16S)^0.5

where d=inside diameter, P=internal pressure, S=allowable stress, and t=thickness

If P=70psi, d=36", and S=55,000psi for A-285 carbon steel plate, I get 0.55" thick plate for safety factor of 1.0. I'm going to rubber-line the blinds too.

Is this an appropriate equation for this application? What is an acceptable safety factor? If I use 1" plate I would have a S.F. of 1.8. A stock 36" 150# blind flange is 3.5" thick, and that is far too heavy.

 

[catpidgeon]

ANSI B31.1 Para 104.5.3 and I believe B31.3 both use this formula, hence it is code sanctioned - You'll have to check the B31.3 reference as I don't have a copy handy.

 

[aybee]

that formua per the email and per B31.3 is for a blind flange which is supported either side by line flanges not an blind end flange which is what the stock blind flange is and which is designed as a flat plate to a different formula refer ASME V111 div 1 which is why it is as thick as it is..if you use the ASME formula for flat plates for your pressure you will find it is close to the stock flange thickness. I would worry more about the HDPE pipe, it will be temperature limited and the weaker link in your system by the sound of it

 

[hydrodude]

Just a reminder..... Be sure your flange is fused to the pipe and not a mechanical dresser type, I have seen many times that people don't realize they are not made for longitudinal holding. Quite a surprise when they blow off at a low pressure

 

[BRT549]

Thanks for your tips, all.

aybee: so that formula (t = d(3P/16S)^0.5) is only good for a blind that is inserted between two flanges in a line? I guess what I'm looking for is a blind END flange equation?


Hydrodude: <<Be sure your flange is fused to the pipe and not a mechanical dresser type>>
I'm not quite sure what you are referring to here. The HDPE hasn't been fabricated yet, but I called out 36&quot; flange adapters for both ends. They would have carbon steel backing rings that put the 'squeeze' on a HDPE lip that forms the actual seal against the rubber-lined C.S. blind.
Could you elaborate?

 

[samuelliu]

You may also try Part IV of Modern Flange Design (Taylor Forge Bulletin 502#) and UG-34 ((c)(2)) as well as Appendix 1-6, of Sec VIII (Div. 1), ASME BPVC.

 

[aybee]

yes blind end flange..per ASME V111div 1 for internal pressure on flat ends ...you will get a thick flange as these designs cater for bending of the plate.

 

[Hookem]

Thickness is often dictated by number, size, spacing, strength of bolts; and, often overlooked, by the gasket. Best to review ASME Section VIII, Div. 1, or TEMA Heat Exchangers. I have spreadsheets for round, oval, abround, rectangular, etc. geometres and for confined gaskets and full faced gaskets. However, they are crude. Best commercial program I have used is CODECALC.