HDPE for instrument air pipe

[firefastball]

Is it common to have a HDPE pipe to distribute instrument air?
Currently one of the instrument air pipe is highly corroded due to the environment it is in.
I'm thinking of replacing the pipe with a HDPE PE 80 material with a pressure grade PN 12.5 or 16.

 

[LittleInch]

Common, no, possible - can't see why not unless you have fire issues and your connection is safety critical, though loss of an air pipe should be a fail safe mode for most valves. Armoured hose might be a better solution but depends on how your tube is supported / protected. Remember PE "creeps" over time so you might need a lot of support clamps to stop it sagging. Your end connectors will probably need flanges as compression fittings don't work so well.

don't forget solar temp gain - PE doesn't like temperatures much above 40 to 50 C and de-rates quite quickly. Black PE tubing (you need black for UV protection) can get to 60 to 70 in a really strong sun, but depends where you are - Alaska probably not, but desert conditions....?

I suspect there are better alternatives than PE tube, but you need to ask some instrument engineers unless this is a large header.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[bimr]

Asahi has an HDPE product for instrument air. Air-Pro is the only HDPE piping system approved for use, and warranted by the manufacturer, for compressed air applications. Air-Pro is CAL-OSHA listed.

http://asahi-america.com/piping-systems-and-welding/single-wall/air-gas-handling/air-pro-hdpe

Asahi thermoplastic piping systems using high-density polyethylene (HDPE), overcome the brittleness problems associated with PVC. They efficiently and reliably deliver compressed air with lower material and installation costs and longer service life than with metal systems. They offer a margin of safety missing from PVC.

These new thermoplastics are safe because they expand at the point of failure, tearing open rather than fragmenting dangerously. They do not accumulate scale on their ID, nor does pitting or corrosion occur, and they are unaffected by synthetic and mineral oils used in compressors.

http://hydraulicspneumatics.com/200...s/Article/False/6547/TechZone-FluidPowerAcces

 

[moltenmetal]

We use polyethylene or polyurethane tubing for the drops from instrument air headers to the devices, and Legris push/lock fittings for the connections. We substitute PU when it's outdoors in a very hot location or near hot equipment. I'd be suspicious about using HDPE pipe for headers in an outdoor direct sun exposure. Indoors in a building? An approved product would be no problem- thanks for pointing us to one bimr!.

There are stainless options if that works for you, including press-lock (i.e. Victaulic Vic-Press and others) piping systems if you can't tolerate threads and are too small to use roll-grooved piping (Victaulic, Grinnel etc.). We don't like the press-lock stuff much- we find the fittings too large and too expensive.

If you are indoors and in a corrosive environment where nonmetallics are the only really feasible option (i.e. an electrowinning facility where there's a lot of chlorine as a fugitive emission), there is or at least was an ABS piping system approved for instrument air- can't remember the mfg but a Google search should find them pretty quickly. The benefit of the ABS is that it's a solvent-welded rather than thermally welded system so the installation should be faster and cheaper than HDPE without the creep risk. But again, no ABS in direct sun exposure in my opinion.

 

[rconner]

While the risks represented by small diameter thermoplastic compressed gas piping are perhaps arguably less than with large, you probably need to be aware of what appears to be a sort of collective industry stance at

http://plasticpipe.org/pdf/recommendation-b_transport_compressed_gas.pdf.

Be sure to read the fine print of any dedicated products as well. Nearly four decades ago I happened to see a sizeable polymeric air hose of some sort break in the middle of a crowd of workers in a desert jobsite in the Middle East. While thankfully no one was seriously hurt in that particular incident, it was nevertheless an unbelievably chaotic scene one doesn't readily forget. As I understand others in compressed gas incidents have not been so lucky (resulting no doubt in trade and regulatory advisories like this), more rigid and/or well supported and coated pipes may also be options to consider.