Safer pneumatic tests?

[EJEric]

New to the forum.

We are a custom piping manufacture job shop that at times must perform pneumatic tests.

Has anyone ever used or consider a volume displacement "device" to reduce the stored energy?

Test pressures are typically below 200 psig but volume can exceed ~ 1000 ft3.

We can make closed cylinders for each project but handling and cost is always an issue.

Initial thoughts are design approved non-metallic spheres, sealed PVC pipes,...?

Thank you in advance.

 

[rconner]

I beleive volume displacement devices have been used for many years and various reasons in at least some works pressure testing; however, there may be practical problems/limitations associated with such, and in general hydrostatic testing with or without volume displacing mandrels is still going to be better and safer. [it may behoove one to be particularly careful with intended pneumatic application of pvc, and design of same (e.g. in light of OSHA's advisories on pvc air pipe etc.)

 

[unclesyd]

I have used plastic balls for volume reduction for another purpose.

you might want to look at the plastic vapor containment balls for you lower pressures and a solid ball for the higher pressure. You can get a good volume reduction with a mixture of sizes.
They are other suppliers that make plastic balls for large scale covers on waste ponds.

Here is one supplier for plastic balls.

http://www.orangeproducts.com/index.htm

Another approach might be is to use syntactic foam a product
that can take exceptional external pressure with collapsing.

http://www.cmtmaterials.com/syntactic.htm

http://www.cumingcorp.com/flotation.php

 

[unclesyd]

Correction to my last post:

Another approach might be to use syntactic foam a product
that can take exceptional external pressure without collapsing.

 

[EJEric]

rconner - thanks for th reply. Will check out the OSHA advisories.

unclesyd - Thanks. Haven't heard of syntactic foam and will investigate.
Ideally, since our diameters are often 100" or greater, we would like to use larger diameter plastic balls. Weight might be a concern if solid.
We considered fiberglass spheres or vessels but have discarded them due to brittle nature. PVC may not be much better.

 

[unclesyd]

You might get by with something less than a syntactic foam by using a high density closed cell foam product from General Plastics or Dow among others.
The foams from GP will take loads of 300 and 1000 PSI with a very small deflection. I'm not sure about the Dow material as the only information I have is a little test I ran yesterday where at a 130 psig there was no discernible volume change in a small block of a much lower density material than the Dow 100.

This could be one avenue of approach in the resolution of your project. There is such a wide choice of materials available giving you numerous possibilities.

Last-A-Foam 3300; Last-A-Foam 3900

http://www.generalplastics.com/products/product_detail.php?pid=16&

http://www.generalplastics.com/products/product_detail.php?pid=18&

http://building.dow.com/styrofoam/na/pro-us/products/styrofoam/highload_100.htm

 

[budt]

Could you fill it 98% full of water and then apply the air pressure??


Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING

 

[EJEric]

We are investigating several now. Most of the places we call have no information on how much external pressure is acceptable and at what deformation. We will procure samples and test.

budt: We can't use water since the internals contain items that would be harmed by the water (such as refractory or bagged insulation). Required assembly order prevents hydro of finished unit prior to the installation of these items.