RE: [PSUBS-MAILIST] Design depth

[irox <irox@ix.netcom.com>]

Hi,

(as far as I know) PVC is a bad choice for external hydrostatic
load applications because it is brittle, which means it's only
failure mode is "catastrophic" (i.e. no buckling or deformation).
So, yeah, your gut instinct of thinking twice about PVC is a good one.

Cheers!
  Ian.

-----Original Message-----

From: Daniel Kubiak 

Sent: Dec 16, 2010 2:47 PM

To: personal_submersibles@psubs.org

Subject: RE: [PSUBS-MAILIST] Design depth








Jon,

 

I had a piece of 14" PVC in my garage that I thought I could use.  With a rough guess of 1/4" wall thickness, Under Pressure gave me about 25'.  However, I went out and measured the wall thickness and it is only .187".

 

I'd like to think that when it came down to building my submersible I would have picked up the piece of pvc and thought twice about using it regardless of report from Under Pressure.

 

I attached a copy of the report so you all can see what Under Pressure creates and see what factors it takes into account.  Also, if your new version isn't working, Jon, you probably need to download the free SQL Server Express 2005 from Microsoft.

 

Dan

 


 



Date: Thu, 16 Dec 2010 14:54:00 -0500
From: jonw@psubs.org
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Design depth



I have not been able to get the latest under-pressure software to work on my computer, however previous DOS versions did not take enough factors into account for serious manned or unmanned designs, in my opinion.  It has some use to provide a general idea of some limitations, however I believe the ABS spreadsheet available from PSUBS takes many more factors into account and will provide a better design.  For thick wall vessels (no ribs) you can also use the "unstiffened cylinder" calculator on PSUBS which also is based strictly upon ABS formula.

For PVC, you can compare the results of the under-pressure program with the information in http://www.us.piping.georgefischer.com/external/us_handbook/03.pdf

What size PVC where you contemplating using?

Jon

On 12/16/2010 2:24 PM, Daniel Kubiak wrote: 


I'm just getting started in this arena, but I came across a nice program called "Under Pressure" for examing pressure hulls.  As a newbie it is interesting to see how various shapes and materials respond under pressure.  My first project is going to be an unmanned vehicle to photograph the shipwrecks in the great lakes.  I assumed PVC would be sufficient for this and was shocked to see in Under Pressure that it would fail at a mere 25 ft (based on the schedule I had planned to use).  I'm not putting life at risk yet, but this saved me some $$ replacing electonics and really opened my eyes to realize that I need to KNOW what will and will not work.
 
Is Under Pressure a commonly used program?  I downloaded it from www.deepsea.com in the resources section.



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