Poly tubing is common as dirt on gas systems (vacuum). Depending on what type you buy it's good for one to four years. Go to home depot and you'll have to replace annually since it gets very brittle after 2-3 years. Buy the thicker version with more plasticizers from a commercial pool supplier and you'll be replacing every four years. Most of ours are such short runs that I use the better form and replace annually anyway. I'm already in there rebuilding regulators, injectors, and roto-meters so the added labour and expense is a drop in a bucket.

I'm asking this because another facility believes they have this problem with a CL2 gas line (the better quality stuff) filling an underground PVC pipe with gas. I'm thinking it's actually a different problem altogether but I don't deal with tubing that is essentially sealed into a small space.