Safety Alert please read!

[Tristan Lall]

Originally Posted by G Fawkes

"It is our position that PVC pipe shall not be used as a means of transporting compressed air. "
http://www.osha.gov/dts/hib/hib_data/hib19880520.html

The danger is that it shatters upon failure. There are types of plastic pipe rated for compressed gas use but I do not think the standard PVC pipe should be used for compressed air.

I suspect that with the inclusion of plasticizers, a PVC pipe could be produced that did not exhibit this failure behaviour.

It's an overreach to take the position that "PVC pipe shall not be used as a means of transporting compressed air" without qualifying the pipe's composition, manufacturing process, installation and operating conditions. Despite their strongly-worded statements, I hope that OSHA is recognizing competent engineering as the appropriate way to circumvent their prohibition.

[Ivan_Yuri]

The Cy-Ranch Cy-Borgs have had several issues with the PVC-esque tubes for pressure, one had a hairline crack in it that ran down a good length of the piece of tubing, thankfully we found it and marked it out of the crowd, we have quite a few pieces of that stuff labeled to go on our robot, but I'm going to send our lead mentor this thread just to be safe! So sorry for your setback, best of luck on recovery!

[Tristan Lall]

Originally Posted by Ivan_Yuri

The Cy-Ranch Cy-Borgs have had several issues with the PVC-esque tubes for pressure, one had a hairline crack in it that ran down a good length of the piece of tubing, thankfully we found it and marked it out of the crowd, we have quite a few pieces of that stuff labeled to go on our robot, but I'm going to send our lead mentor this thread just to be safe! So sorry for your setback, best of luck on recovery!

What's the part number of the component? (Are you talking about the plastic air reservoirs or the plastic pneumatic tubing?)

[FrankJ]

Originally Posted by Tristan Lall

I suspect that with the inclusion of plasticizers, a PVC pipe could be produced that did not exhibit this failure behaviour.

It's an overreach to take the position that "PVC pipe shall not be used as a means of transporting compressed air" without qualifying the pipe's composition, manufacturing process, installation and operating conditions. Despite their strongly-worded statements, I hope that OSHA is recognizing competent engineering as the appropriate way to circumvent their prohibition.

PVC pipe manufacturers also say do not use PVC pipe for compressed air systems. The big problem is that it shatters on failure. That warning along with the OSHA statement is enough for me not to use on compressed air systems. For OSHA competent engineering means following their warnings.

One possibility is the fitting was overtightened, starting the failure.

[Kevin Sevcik]

Originally Posted by FrankJ

PVC pipe manufacturers also say do not use PVC pipe for compressed air systems. The big problem is that it shatters on failure. That warning along with the OSHA statement is enough for me not to use on compressed air systems. For OSHA competent engineering means following their warnings.

One possibility is the fitting was overtightened, starting the failure.

That's PVC pipe. I believe Tristan's point was that PVC the plastic could be made in a non-shattering formulation with added plasticizers. After all, I can get high grip gloves that are coated in PVC. I'm pretty sure that formulation of PVC isn't going to shatter at anything above dry-ice temperatures.

In other words, banning "PVC" from compressed air usage is about the same as banning "steel" from being used for something. Both words encompass many materials with a broad range of physical properties.

[FrankJ]

I expect your gloves will not hold 90 PSI either The warning is specifically about PVC & compressed air systems. I suppose a mfr could find a formulation, test it, test, certify it. But then it would not be the commonly available PVC that the warning applies to. The warning also allows covering the PVC with a shatter proof material covering it. That would be an engineered solution I suppose.

BTW I have several applications that I don't use "steel" for as well.

[Tristan Lall]

Originally Posted by FrankJ

But then it would not be the commonly available PVC that the warning applies to.

That's just the thing: apparently some state OSHA offices prohibited PVC pipe outright (e.g. Arizona, from which the quotation at issue was sourced) without specifying whether they were only talking about the conventional PVC water pipe. Unless they are confident that no safer PVC pipe can be made, they should only restrict the specific products that pose the hazard.

Originally Posted by FrankJ

The warning also allows covering the PVC with a shatter proof material covering it. That would be an engineered solution I suppose.

Exactly: that better-engineered solution conflicts with the prohibitions described by the Arizona, Washington and possibly Nevada OSHA offices. The main OSHA memorandum is better, because it recognizes appropriate ways to use the pipe.

[Al Skierkiewicz]

Fox,
The same thing happens if Loctite gets on the Lexan.

[G Fawkes]

There is plastic pipe suitable for compressed gas use and they are typically labeled as such. They are designed to split open upon failure and not throw fragments.

I mentioned this issue for 2 reasons;

1) A lot of folks do not realize that it is not a good idea to use the rigid PVC water pipe from the hardware store for compressed gases (unless buried or encased) because it shatters upon failure.
2) The air tank in question is listed as being made of polypropylene but the way it shattered upon failure is cause for concern.

[pfreivald]

Originally Posted by Tristan Lall

That's just the thing: apparently some state OSHA offices prohibited PVC pipe outright (e.g. Arizona, from which the quotation at issue was sourced) without specifying whether they were only talking about the conventional PVC water pipe. Unless they are confident that no safer PVC pipe can be made, they should only restrict the specific products that pose the hazard.

Indeed they should, but all too often people who don't understand the science behind a decision are the ones who make it, especially when the government is involved...

I'll never forget teaching in California when a law was passed (unanimously by both houses and signed into law by Governor Davis) that outlawed "chemicals made from dangerous elements" in science classrooms... Further investigation indicated that "dangerous" included anything "toxic" or "flammable".

Not withstanding the absurd misunderstanding that toxicology is a matter of dosage (and that even water ingested in sufficient amounts is toxic), the ignorance of even middle school level chemistry was quite astounding.

Among the things unintentionally outlawed in California science classrooms: matches, table salt, water, air, humans.

[Al Skierkiewicz]

Scott,
I hope you kept the pieces. I suspect Andy and Mark would like to take a look at these and contact the manufacturer. I certainly would like to see them.
The OSHA statement comes from an industrial accident in Texas at a chemical plant or refinery, I can't remember which. The plant was plumbed for pressure lines between buildings and process positions. As an employee was walking past one of the pipes, it burst sending shards into his arm. With a little research you can find the original report and findings of the resulting investigation.
From the pieces shown, it is possible that the first failure occurred at the fitting but the resulting failure of the rest of the tank is unusual. Was the tank chucked up in a vise at some point to assist with fitting insertion? Is it possible that the two tanks were close enough that the failure of one caused a failure in the other? What compressor were you using? The large Thomas compressor can get up to 150-160 psi if the pressure relief valve is not calibrated but that should be well below the failure point for these tanks.

[fox46]

This reminds me of an experience I once had with some lexan sheet. Lexan is normally a very resilient material very resistant to a brittle fracture. On one of my projects I had used lexan panels as body parts on a vehicle. A friend of mine who was helping out decided to clean them using aerosol brake cleaner. After wiping them down with the brake cleaner and a rag, approximately one hour later the entire panel shattered into tiny pieces. We deduced that the chemical agents in the brake cleaner had been absorbed into the plastic causing it to become incredibly brittle. It is possible that a similar process may have affected these two tanks.

[ftc3799]

Update on the exploded tanks, I had time today to do some analysis of the fragments, first of all this is of my own opinion and I have reviewed this with some of my colleagues to confirm my findings. This had nothing to do with the handling of tanks all marks on the tanks came from the parts being scattered across a machine shop floor. It also had nothing to do with temperature the tanks had been at room temperature for a few days. Like most before looking we were thinking damage by over tightening but this was not the case. What I found was a elongated air bubble in the material. The bubble looked like a worm hole around part if the threaded openings base expanding in size and thinning out the threaded wall. My assumption is the fitting stressed the wall enough to open a crack to the bubble that ripped apart when under pressure. When the tank exploded the fragments caused the tank next to it to blow apart.
The one thing I would like to know would be does the manufacturer do any type of vision inspection either by ultrasound or x-ray of the tanks. Because if they don't how many more of these tanks could have hidden rupture points.

[Dave Campbell]

I will make sure the folks at Clippard see this thread first thing Monday morning. They are one of our team sponsors.

[Andy Baker]

Originally Posted by Dave Campbell

I will make sure the folks at Clippard see this thread first thing Monday morning. They are one of our team sponsors.

We at AndyMark have contacted the manufacturer about this issue, as has FIRST. More news will come from this today or tomorrow. Hopefully, we will have explanations and a direction of what to do.

Andy Baker