Exploding a possible myth?

I ran across one of the best reports I have read about the reasons for not using propane or a refrigerant tank for a receiver in a compressed air system. Here is the link in Horn & Whistle Magazine.

I have been in the HVAC business all my life and at first thought all those throw away refrigerant tanks must be good for something. In fact there was at least one manufacturer who was offering a kit to convert these tanks to portable air use. The kit consisted of a valve, gage and a short hose. I used one for several years. This item is no longer marketed.

I have seen air tanks and high pressure (HP) steam vessels that have corroded. All the tanks I have worked with that developed leaks in normal use did just that, developed leaks. They did NOT just suddenly and catastrophically explode. The writer never uses the word “explode” however the term “life threatening” conjures up the impression. I believe the explosion impression makes a good scare story and borders on urban legend.

The “Myth Busters” have shot diver air tanks with bullets and they do not explode. They take off like a rocket.

The expansion and contraction theory presented in the link is a new one for me. It is written as obvious speculation but it does sound plausible. Whether it has caused sudden and complete failure is not substantiated in the article. The fact is the pressure in these tanks in their designed use varies considerably and follows and endures temperature changes from frost on the outside (-40 deg) to 120+ degrees. This too is probably a myth until someone can prove that it has happened.

I am always a skeptic whenever I read this sort of thing. The air pressures (~100 PSIG) are not above the design rating of the tank when new. It is the aging and corrosion (and now expansion) that are held up as the danger. I believe they are concerns but not for explosion. (Explosion is a nice scary thought though!) 

Do not take me wrong here. I in no way suggest using these tanks for any compressed air use. What scares me is the thin metal from which they are made and the abuse they will suffer in years of handling and use. Anything under pressure needs to be respected. For me because I have had the experience, the likelihood is that a leak will develop and be noticed before the potential of an explosive type failure. But potential is still a risk I will not take. 

The point is it can be hazardous to repurpose thin metal tanks DESIGNED for a one time specific use and then to be disposed. Use a heavy tank designed for compressed air and especially the moisture it contains. 

Dan’l