Pressure strength of steel...

[cpasseno03]

Hi, this time I am trying to figure out how much pressure different thicknesses/arrangments could take before implosion. How deep they will go... I am making a Remote Operated Vehicle and need to calculate maximum depth's for different portions. Such as the frame itself, 1 1/4" square 16 gauge glavanized tubing, and camera housings, 2" X 3" X 2" of 1/4" steel...motor housings, 2 1/2" pipe, and so on...anybody know of some info on how to go about doing this? Sure would appreciate it!<br />Thanks!<br />Craig<br />passrdcc@nmo.net

 

[magster65]

Re: Pressure strength of steel...

Not too sure about the strength of the metals but if it helps... every 2.31 feet of depth equals 1 p.s.i. or 1 foot of depth equals .433 p.s.i.

 

[grandx]

Re: Pressure strength of steel...

Craig,<br />This is not exact, but a good enough for your application: This is one of many formulas for the compressive strength of pipe (tubulars). Short sections of pipe with capped ends (like what you describe) will handle more pressure than the formula below.<br /><br />P=2*Yp*((D/t)-1))/((D/t)^2)<br /><br />of course you would apply a safety factor on top of this.<br /><br />P=pressure (psi)<br />Yp= yield point of material, for mild steel you can use 30,000 psi.<br />D=outside diamter of tube (inches)<br />t=wall thickness of tube (inches)<br /><br />i.e. a 2" diameter, steel pipe, with 1/4" wall:<br />can withstand 6,563 psi. approximately 13,000 ft depth, if you assume about 1/2 psi per foot depth.<br /><br />Hope this helps you figure your needs.

 

[SCO]

Re: Pressure strength of steel...

Spheres and tubes will do better, like a roman arch.<br />For other configurations, I bet roarks, the best of the best stress and strain handbook, will have what you need. Here is a link to an online site with a forum where I bet engineers in the formula will look stuff up and help you. <br /> http://www.roarksformulas.com/

 

[GF]

Re: Pressure strength of steel...

Craig, For the frame tap in fittings and fill the frame with hydraulic oil, then adapt a soft accumulator to keep the frame full of oil as pressure increases. For the camara housing make sure you have the proper specifications and include a safety margin. I have watched pressure vessel implode and it is just as devestating as an explosion. Happens instantanious, only in the movies do you get a small crack and then spreading. Good luck on your project

 

[cpasseno03]

Re: Pressure strength of steel...

THANKS everyone, great help. grandx, this formula is for external pressure I assume? My guess would be that a sealed enclosure of any kind will implode at a different pressure then that which it take to EXplode it, or are they the same? I have thought about the oil filling for certain things, but I hope to make most everything from steel, which most likely will take the pressure fine, and being filled with air will help offset the negative buoyancy of all the steel. Once again thanks for all the help!, I am checking the Roarks thing right now...<br />Craig

 

[grandx]

Re: Pressure strength of steel...

Craig,<br />Yes the formula I gave you is for external collapse pressure for a cylindrical tube. Round and cylindrical shapes are more stable than cubical shapes etc. and will handle external and internal pressure more efficiently. You are correct, that collapse pressure and internal pressure resistance are not the same, generally speaking cylinders can withstand more internal pressure than external, but I'm sure there are exceptions. <br /> <br />Internal pressure= <br /><br />(2 x wall x Yield stress)/(inside diameter)<br /><br />Good luck with your project.