All: I am involved with a forensic project on a large school utilizing large primary interior mains for a 2-pipe hydronic system servicing packaged heat pumps. After reviewing nearly 10 years of service and maintenance records I found an alarming trend of chronic pipe failures as a result of ESC (environmental stress cracking). The mains consist of CPVC (chlorinated polyvinyl chloride) plastic pipe and fittings. Run-outs to heat pumps in all parts of the multistory facility are mostly copper piping with no failures, just the CPVC piping. We are in the process of submitting failed components for professional analysis. In the mean time I found several documents through net searches on this subject, several of which are related to the use of CPVC used in fire suppression systems where conditions require some type of antifreeze constituent to protect the piping. Depending on the manufacturer, specific type of CPVC, temperature range, percentage p-glycol and other factors, the consensus seems to range between 1) absolutely never use propylene glycol/water brines in CPVC piping to 2) it might be ok depending on low p-glycol concentrations and moderates temperature ranges.I have attached some of the more interesting documents I found on the net and will likely find more, maybe from the Plastic Pipe Institute or other credible industry source. If anyone else has experience with CPVC would encourage all to share through the IGSHPA Connect community.