"DaveC" wrote in message
news.net...
I've got an old 20 gal (?) compressor tank in which I want to install a
drain. I'm guessing it to be 1/4-inch (6.3 mm?) thick steel. Tank is rated
to
125 psi.

Can I drill and tap this for 1/4 or 3/8-inch pipe? Or should i get a
"plug"
welded to it that I can drill & tap?


I'd be totally surprised if your tank has the wall thickness you speak of.
They typically are thinner, especially if it's rated for 125 PSI. If it
has, it would be adequate for a 1/4" pipe thread, but marginally. Best
policy is to weld in a bushing, assuming you have the capability.

Are there rules to follow for such stuff?

Pressure vessels are generally built to the pressure vessel code, so, yes,
there are rules. Ernie is our chief cook and bottle washer where welding
is concerned. With luck, he'll chime in.

Is there a better n.g. to ask this
question in?

The one he frequents most, which I don't recall. I think it's scientific
welding and joining, or some such. Others will probably provide the proper
group for you.

Harold