Water Pressures
Water Pressures
(OP)
Hello,
I am trying to get some rough calculations. We are trying to calculate the pressures on a PVC pipe that is 12" in diameter, 300 ft. underwater.
I know that at ground level we have 14.7 psi.
Every 10 meters down, you double that.
Essentially, at 300 feet below, you experience about 148 psi. of pressure pushing inwards in every direction.
Now this changes because a PVC pipe is a cylinder, basically an infinite arch. PVC pipes have pressure ratings but they are inward forcing outward, I am trying to calculate the other direction.
We are still trying to find out what kind of pipe we need when it comes to technical dimensions, (Material, temperatures, water tight, inner wall thickness, etc.)
Here are a couple calculations
Tensile Strength, psi @ 73°F 7,450 ASTM D638
Tensile Modulus of Elasticity, psi @ 73°F 420,000 ASTM D638
Flexural Strength, psi @ 73°F 14,450 ASTM D790
Compressive Strength, psi @ 73°F 9,600 ASTM D695
Izod Impact, notched ft-lb/in @ 73°F 0.75 ASTM D256
I should be able to calculate the failure point using the above and the dims of the pipe (12.75" OD, .187" average wall thickness for 12" duct pipe.) CL100 in 12" has a typical wall thickness of .311".
Thanks
I am trying to get some rough calculations. We are trying to calculate the pressures on a PVC pipe that is 12" in diameter, 300 ft. underwater.
I know that at ground level we have 14.7 psi.
Every 10 meters down, you double that.
Essentially, at 300 feet below, you experience about 148 psi. of pressure pushing inwards in every direction.
Now this changes because a PVC pipe is a cylinder, basically an infinite arch. PVC pipes have pressure ratings but they are inward forcing outward, I am trying to calculate the other direction.
We are still trying to find out what kind of pipe we need when it comes to technical dimensions, (Material, temperatures, water tight, inner wall thickness, etc.)
Here are a couple calculations
Tensile Strength, psi @ 73°F 7,450 ASTM D638
Tensile Modulus of Elasticity, psi @ 73°F 420,000 ASTM D638
Flexural Strength, psi @ 73°F 14,450 ASTM D790
Compressive Strength, psi @ 73°F 9,600 ASTM D695
Izod Impact, notched ft-lb/in @ 73°F 0.75 ASTM D256
I should be able to calculate the failure point using the above and the dims of the pipe (12.75" OD, .187" average wall thickness for 12" duct pipe.) CL100 in 12" has a typical wall thickness of .311".
Thanks





RE: Water Pressures
CODE -->
You may need to use a stouter material, or use a much smaller tube.
The numbers above were produced by a spreadsheet that I do not wish to distribute,
based on these papers:
ref 1: "Tubing Limits for Burst and Collapse", Tech Note, CTES, L.C., Conroe TX www.ctes.com
ref 2: "Effect of Initial Eccentricity on Collapse Pressure of Circular Beam Tubes", S. Yadav
Fermi National Accelerator Laboratory, Batavia IL www.flab.gov
The reference to an inner tube came from an investigation into collapse
of a jacketed tube under hydrostatic test of the jacket, which was the whole
point of doing the analysis in the first place.
Mike Halloran
Pembroke Pines, FL, USA
RE: Water Pressures
RE: Water Pressures
Using the same 12.75" OD, you will need a wall thickness of at least .790" in PVC.
That will of course be heavy, but there is another consideration; have you figured out how much your pressure hull must weigh in air in order to be neutrally buoyant? Hint: it's the weight of an equivalent volume of water, or seawater, depending on where you are submerged.
Steel submarines are commonly ballasted with many tons of lead in order to allow them to submerge. That's probably another subject you'll need to read up on.
Mike Halloran
Pembroke Pines, FL, USA
RE: Water Pressures
HunterMoore; Is this for an ROV?
Keith Cress
kcress - http://www.flaminsystems.com
RE: Water Pressures
At sea trial, the turboshaft engine didn't like the backpressure from the collapsed tube, between two elbows of a J-shaped pipe where it couldn't be seen, so we got to make another one for free. The inner tube was 13" OD x .075" wall, stainless steel. The outer tube was 14" OD, same material, mirror polished.
Mike Halloran
Pembroke Pines, FL, USA
RE: Water Pressures
Mike's cited references:
http://ctes.nov.com/Documentation/technotes/Tech%2...
https://web.fnal.gov/organization/TDNotes/_layouts...
TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm
RE: Water Pressures
HunterMoore; Take a look at oil filled underwater systems. You could make the pipe out of shellacked cardboard and not have it collapsing.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Water Pressures
I am not sure what you mean by oil filled systems, any more info? I would like to look into it.
Hunter Moore
Project Neptune
RE: Water Pressures
TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm
RE: Water Pressures
They were vacuum filled with high purity mineral oil and had elastomer pressure equalization bladders.
They didn't mind 14,000' of head on them.
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P.E. Metallurgy, Plymouth Tube
RE: Water Pressures
Surprisingly you can put most electronics in pressurized oil and they wont care and all sorts of problems go away.
There's a thread in ET somewhere that went into this pretty deeply.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Water Pressures
EdStainless- Anymore info on the electric motors? Our next project was finding a relatively small motor to put onboard.
Hunter Moore
Project Neptune
RE: Water Pressures
Disregard our ignorance in the first few posts.
As for oil type. I'm not sure really. It probably doesn't matter much as the hydraulics of it doesn't care at all.
Secondary conditions may be more important, like if you want to retrieve the board and clean it to alter it. In that case something not poisonous and washable in your sink probably makes more sense. Cooking oil perhaps.
Doing this is not a slam dunk, you do have to think it through and make sure you're not doing anything stupid. Stupid, would for instance, be using aluminum capacitors. They enclose space that can include air making them likely to fail if compressed by external pressure. There may be some other items that will have the issue too. You need to consider all your components.
Do note that if your pipe is small enough you can take your 'cylinder' to a fire extinguisher shop where they do hydro testing of fire extinguishers. They have a safe pressure testing vessel that they can set accurately to any test pressure under about 12,000psi. The pressure testers have to be able to accommodate a 70cuft CO2 tank which is like a very large welding tank.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Water Pressures
> Safe disposal/toxicity/environmental impact
> Leakage impact to environment
> Corrosion properties
> Cleaning off the electronics afterwards
> Heat transfer
TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm
RE: Water Pressures
Anything else I should know?
Hunter Moore
Project Neptune
RE: Water Pressures
Keith Cress
kcress - http://www.flaminsystems.com
RE: Water Pressures
It was safe and easy to handle, with no health issues (you could drink it), and it didn't attack plastics or rubbers.
Such as this
https://cglapps.chevron.com/msdspds/PDSDetailPage....
= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube