depth for Schedule 40 and 80

[Schwob]

This info is highly likely somewhere here or linked to here... I am just not finding it...:

If not used in tension (internal pressure), as they are rated for, but in compression (submersion) how deep can run off the mill schedule 40 PVC pipe and fitting made "containers" (and schedule 80?) be taken before they spring a leak or worse?
... does that change as the diameter gets bigger (likely for burst, not sure about leak). Mostly interested in diameters 2, 3 and maybe 4 inches.

To simplify things, lets say I just make a buoancy chamber. No removable lids etc. just a length of pipe with two on the outside overlapping endcaps properly glued on. Up to what depth should it survive - repeatedly...? How do you figure?

 

[northernone]

Anecdotally, 200ft from the old sewer pipe scooters.

 

[Schwob]

Anecdotally, 200ft from the old sewer pipe scooters.

Thanks...
Do you remember, was that schedule 40 or 80?

 

[Akimbo]

I don't have the numbers handy but you need the diameter to calculate it. It was pretty common to see 6-8" diameter acrylic (Plexiglas) camera housings with a 1/4" wall in the 150-200' range. Flat ends were 1/2" plexi -- circa 1960s. The book on the left is a how-to manual on making them.

See Post 6: DIY O-rings for Divers for techniques to make O-ring sealed ends.

 

[northernone]

For a guess at the relationship between burst pressure and crush pressure here's a chart for cpvc. Safety margin and real world factors reduce these.

There's more info online in the ROV forums, people doing 'dry' frames for their projects.

 

[Akimbo]

For a guess at the relationship between burst pressure and crush pressure here's a chart for cpvc. Safety margin and real world factors reduce these.

(general comment, not directed just at northernone)
Plastics are also very sensitive to temperature. I would expect significantly shallower sudden catastrophic failures at crush depths in colder water. Warmer failures will be preceded with deformation and others will just implode. I can't cite names and dates or accuracy but stories circulated in the 1950-60s underwater photo crowd that a Plexi housing imploded in a diver's hands and he lost some fingers and nearly lost consciousness, presumably from the shock wave. It could be a sea story to illustrate a very real hazard... or maybe not. Proceed carefully.

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SAFETY WARNING

Implosions are VERY dangerous for divers. Hydrostatic testing and large safety margins are justified.

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[JamesBon92007]

I don't have the numbers handy but you need the diameter to calculate it. It was pretty common to see 6-8" diameter acrylic (Plexiglas) camera housings with a 1/4" wall in the 150-200' range. Flat ends were 1/2" plexi -- circa 1960s. The book on the left is a how-to manual on making them.

View attachment 445246​

See Post 6: DIY O-rings for Divers for techniques to make O-ring sealed ends.

I am very surprised that those box designs would survive to 150', as in NFW! Or are you talking about a 6" cylinder? I didn't have a book when I was building such housings and never took them deeper than about 40'. Personally I would expect a cylinder (PVC) to withstand considerable depth but I'm not an engineer. According to that chart is looks like 3" sch 80 would only hold up down to 500' which is less than I would have thought.

 

[JVos]

That's 500 psi, not feet. So 34 Atmospheres.

 

[JamesBon92007]

That's 500 psi, not feet. So 34 Atmospheres.

OK, thanks That would be over 1100', right?

I missed the part about the box style being 1/2" acrylic. I thought we were talking about 1/4" walls, perhaps five or six inches wide, going down past 150'. I expect that it could be done if supported somehow. I apparently was mislead by the picture of the girl holding the housing and what Akimbo is talking about is a 6"-8" diameter 1/4" wall cylinder with with 1/2" ends. That I can believe

 

[Akimbo]

Or are you talking about a 6" cylinder?

Yes, 6-8" diameter refers to tubing. The flat ends were 1/2" Plexi.