Hydrostatic testing

[daccel]

I'm considering doing some hydrostatic testing on copper pipe with epoxy plugs, using an airless paint sprayer (variable pressure to ~3000 psi).

Do I need to worry about containment in case something fails?

[jackssmirkingrevenge]

Very interesting I would locate the pipe being tested in some sort of box to contain any epoxy plugs that decide to convert themselves into projectiles.

[far_cry]

are you nuts
copper can handle this pressure maby !!!
epoxy no way

[ALIHISGREAT]

are you nuts
copper can handle this pressure maby !!!
epoxy no way

any evidence to back that up? thought not.

[SpudFarm]

copper pipe may hold that pressure, it all depends on the conditions. the best thing you can do is to test from small to big pipes writing down the defects they get and the info aswell as pictures.

[Hotwired]

are you nuts
copper can handle this pressure maby !!!
epoxy no way

any evidence to back that up? thought not.

Top left, 3928psi working pressure

But thats the working pressure, actually having it balloon out and tear will need a lot more so quite a bit of that list should still be intact at 3kpsi.

Doesn't necessarily mean it's safe to be in a cannon as it might then get upset about physical damage in addition to the pressure inside.

[jackssmirkingrevenge]

Properly done plugs should hold. Epoxy is a great material but the key is actually preparing it well as I stress in the how-tos, meaning making sure your surfaces are clean and abraded, mixing the parts in the correct ratio, well and at the right temperature and allowing full drying time.

Still, I'm secretly hoping it fails and you film the result

[ALIHISGREAT]

are you planning on reinforcing the epoxy in any way?

i was thinking bolts through the copper, but that would put a lot of stress on the copper, its just a question of whether the copper could handle it?

[psycix]

Its hydrostatic testing. Though it may be very informational on the strength of epoxy plugs, it wont be very dangerous or spectacular when it fails.
Heck, the plugs may be pushed out slowly.

[jimmy101]

I would think you would need screws or something to help hold the plugs in place. The weakest link is the epoxy to copper interface and that interface will change as the pipe is pressurized.

[daccel]

I don't plan on using it at 3kpsi, just making sure it's safe for co2.

I think I'll test it in a metal pail filled with water, that's easy enough.

The pipe in question is 3/4" type L. I'll probably make three versions - one with no prep besides cleaning (worst case scenario out of curiosity), one with the pipe abraded, and one with holes drilled in the pipe. Screws won't work because it needs to be flush.

Anyone know how to calculate the shear strength at, say, 1/8" diameter? Looking up JB weld it says it has a tensile lap shear of 1040 psi, but I don't know what to do with that number.

[Gippeto]

If you were to consider a lap joint where an end cap and a pipe were jb'd together, the area of the actual joint (Circumference multiplied by length), multiplied by 1040lb/in2, would be the approximate failure point of the joint measured in pounds of force.

Take the failure FORCE, and divide by the area of the actual joint (pi *r*r). You now have an approximate failure pressure.

(Assuming everything was as perfect as when it was tested in the lab.)

De-rate for safety.

Jimmy raises a good point as well. The copper pipe likely will expand with pressure, bringing adhesion strength into play. It's still in psi, just remember that means pounds per square inch, and you'll be able to calculate what you need. Follow the units.

Make certain you get ALL the air out before you begin your testing. The results will be fairly non-dramatic if you do. Possibly frightening if you don't.

The copper tube handbook is an excellent resource to have when working with copper. It is a rather large pdf file if you have dial up.

http://www.copper.org/publications/pub_ ... ndbook.pdf

[daccel]

Thanks for the handy link.

Perhaps I was referring to the wrong property. Maybe tensile strength?

What I mean is if you drilled small holes in the pipe and filled them with epoxy flush with the outside of the pipe and as part of the plug, in place of screws or bolts strengthening the plug. Then the epoxy would have to break at this point rather than just breaking the bond with the copper. So I'm trying to figure out the additional strength this would add.

[Gippeto]

You are talking about shear strength. I thought you were asking about lap shear. Oh well.

You're wanting a shear strength for an 1/8" plug.

pi*r*r for 1/8" diameter is .01227in2

The tensile strength of jb weld is 3960psi. When calculating shear strength, use 60% (This figure varies, depending on who you talk to. Usually between 50 and 70%.) of the tensile strength, so that is 2376psi.

So, we have a shear strength of 2376psi, and an area of .01227in2.

Following the units, we multiply 2376 lb/in2 by .01227in2 to get 29.15 pounds of force. This is the approximate force required to shear the plug in an ideal world.

De-rate this by your comfort level, or at least 50%. (My opinion.)

I hope that helps.

[daccel]

Sorry, I wasn't clear on the properties.

Thanks, the shear strength calculation is exactly what I was looking for. And rather simple now that I think about it.

I'm assuming lap shear is the same whether it's an epoxy plug or cap fixed with epoxy like you mentioned (one vs two surfaces)?