Re: [PSUBS-MAILIST] Steel Pipe Hull

Jon

Your right about the stiffeners, but there must be other problems. Now I get 8 psi :) What are you using for "Center to center spacing of stiffeners"? When I change it the outcome changes, and that does not make any sense. Your calculation can not be right either; 57 psi for a 1/4" think 10 inch pipe? No Way! I get 57 psi out of a garden hose and I've used 10" steel pipes for temporary colverts and had concrete trucks drive over them. There is just no way they would not perform to anything less than 1500 feet.

You can download my sheet from here: http://www.submarineboat.com/sub/BOB2_Hull_Calculation.xls to have a look if needed.

I really do appreciate this exercise I hope the outcome is a simpler and more full proof approach.

Doug,

I get 57psi, 111 feet, for crush depth by external pressure on 10" pipe per the chart specs you referenced. Did you remember to remove the stiffener information in the spread sheet? By default, the spreadsheet employs 1.25 inch stiffener web and 1.5 inch stiffener flange. To compare a common pipe you'd have to remove the stiffener info. The spreasheet won't accept "0", so change the stiffener info to ".0001" or some ridiculously small number like that. Then you'll see the difference between internal and external pressure on the pipe.

Jon

-----Original Message-----
From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org]On Behalf Of djackson99@aol.com
Sent: Monday, January 29, 2007 12:58 AM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Steel Pipe Hull

Thanks for your help, Jay and Jon:

Yes this is the right kind of chart, I just want it to have one more column which would be the working PSI if the PSI force was external, aka submarine.

Look at: http://www.pveng.com/Charts/Pipe%201.03%2020ksi.pdf a 10" steel Schedule 20, .25 wall it shows Max PSI (I think E=1 means no safety margin, right?) of 827. And when if I am using the Hull Calculation sheet right I get 940 PSI for a 10 inch steel hull with a .25 plate thickness. But if I switch the Young's Modulus of Elasticity to 20,000,000 to match the steel pipe it drops to 845 PSI.

So the PSI of the 10" steel pipe seems to be the same regardless of the load being internal or external. So, if that is true, would it hold true for larger diameter pipe? How about aluminum pipe or PVC or UPVC pipe?

Looking forward to your comments, and thanks again for your assistance.
--Doug J