Compressed Air Piping

^^^^ Exactly, no better example than the air your engine compresses. When a engine cylinder fills with air it will compress, fill it with water? You know the answer. As a Driver engineer, I have witnessed the results of a water hammer. I too have been using heavy sch pipe for routing of air lines with no problem. Years ago they taught us about never attacking a LP tank fire from the ends of the tank. Why? Because in one instance the tank under heavy flame impingement ruptured at the end when it BLEVE ( Boiling Liquid Expanding Vapor Explosion). So it became gospel. Later we learned better. Anything can fail, you don't draw a absolute because of it.