I think these are one of those threads where most of us have a hunch, but none of us are true experts. We all look at it through the lens of our own experience. I too have seen the videos of catastrophic failures. However, these are not the norm. When I worked out at the old NOVA Service Centre in the 1980s the guys there told me they discarded tanks at any sign of failure. They said they tend to develop pinhole leaks first and that complete failure along the weld seams that split the tank were rare.
I knew a guy once who flushed his tank every few years with CLR to clean the inside walls. I'm not sure if he is (was?) a Darwin Award candidate. I would think in the same way that rust provides some degree of protection to unpainted light standards, the same may be true of tank walls. Also, I always wondered if horizontal tanks rust faster because of the increased surface area contacting water, but I'm not sure. Additionally, I recall reading a thread somewhere where a guy swore up and down that a constantly pressurized tank lasted longer than one left empty and charged up and down throughout its lifecycle. Can't recall if he was some sort of expert, or just another guy talking out his bum. I guess the logic would be similar to the forensic engineering findings about the original Comet airplane where they discovered that the pressurization cycles were causing cracks in the plane itself. I dunno.
My experience more recently is with a Campbell Hausfeld 60 Gal Single Stage. It's the largest I've owned in my life. I got it in 2012 I believe (judging by my first oil change noted on the maintenance tag in 2013). I change the oil every year, and replace the pressure relief valve every 3 yrs. or so. I tried at least three different automated drains, including a fancy one I controlled with an Arduino circuit I built. None worked reliably past a few months. Eventually I replaced the cheap stock petcock with a right angle brass elbow, about a foot of pipe, and a good ball valve. This makes it easy to drain regularly (so you'd think I'd do this right?). I can even rotate it with my foot instead of getting down on all fours. This is especially nice as my knees have bone chips in them from the days when a Big Mac was a hamburger instead of a sandwich, BMO was called Bank of Montreal, and the nearby KFC franchise was called Barney's Kentucky Fried Chicken. So...yeah, a long time ago.
@kevin.decelles ' post reminded me to do some maintenance, so I just drained mine. (Thanks Kevin.) For a 10+ year old tank the water still looks not bad, although a few years ago I recall some really nasty stuff coming out. I drain mine several times a year, usually spring and late fall, and clean the air filter. I plan to use this compressor until it shows signs of failure. But for now it seems to be just fine. I can't see myself going through the trouble to have it tested. If it makes it to 20 years, I may just replace it with a new one instead.
