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Hi, I am not aware of any brittle fracture issues with polyethylene pipe, including PEX. I doubt you'd have a problem as long as you consider the drop in safe working pressure relative to temperature. All the various plastic pipe materials exhibit a pressure-temperature relationship where the safe working pressure decreases as the temperature increases. The "common" pressure rating that you generally see is one at "normal" temperatures - e.g. 70 or 73 deg F. Contact the manufacturer for the full rating table. Or check to see if there are any P-T rating tables on the web for PEX. That is especially important when single stage compressors with small storage tanks are worked hard. The tank itself and the adjacent piping can get pretty hot and the safe working pressure of plastic pipe used in that vicinity could be exceeded. Just something to check out for your own satisfaction. Possible UV degradation should aslo be considered if it will be exposed to sunlight through windows. Again, information from the manufacturer should be sought out in that regard. In any event, I agree with Fred that a metallic piping system is a better choice, if for no other reason than the factor he mentions concerning better heat transfer and moisture condensation. I prefer copper myself but black iron (steel) piping has been the standard material for such service for many, many years. For those who have used PVC for compressed air at any pressure and not had a problem, I recommend you reconsider your use of it before you do have an incident that could result in serious injury. You will not find any manufacturer of PVC pipe today that recommends using it with compressed air - too much legal liability for them. That should be a sign. It's your risk and your choice, but at least you should be aware of the safety hazard involved, plus the potential legal ramifications if you employ anyone in such an environment. The web is an excellent place to get such information if you want to make the effort. A good place to start is here.  Rod
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