Looks like you didn't receive a valid answer till now, so I'll tell you my opinion.
If I were you, I wouldn't bother to fix up the leaks by welding. Welding, as you've already pointed out, has several shortcomings. Compressed air piping works at room temperature (or very little above) and low pressure (usually 100 psig) and you said the leaks are of "pinhole" size.
So, what I'd do, was to repair the leaks nor by welding but by filling the pinholes with a suitable glue, such as epoxy type or Loctite brand.
If you decide to follow my advice, first of all clean carefully the surface adjacent to the pinhole, using solvent, wire brush, emery cloth or whatever is better according to the case. An area of, say, one square inch in which the pinhole is the center
is more than sufficient. Once the area is perfectly clean and dry, fill the pinhole with one or two drops of epoxy glue or Loctite, according to the instructions written on the box. Which box? The box they're packaged into.
Sounds like an "indian medicine man" prescription? And why shouldn't indian medicine men prescriptions work? Here in Brazil, I've drunk a lot of times the teas and infusions of Amazon jungle leaves prescribed by "indian medicine men" with far better results than the pharmaceutical remedies prescribed by MD doctors.
Merry Xtmas
Giovanni S. Crisi
Sao Paulo - Brazil
Just a few thoughts.......
I would look at where the leaks are. Are the leaks at the joints? Are the joints welded or threaded? If threaded then unscrewing the joints, applying sealant, and re-making the joints should be sufficient (if you have accessibility). Likely, most joints are welded. If so then obviously poor welding was done considering the number of leaks. Degreasing leaks is difficult and residual oil will cause problems but you might be able to get the leaks plugged. (Maybe the original welds were made on oily pipe which would cause porosity and other problems?)
Fire is always a worry. Also the posssibility of explosion. Heat from welding will volitize the oil inside the pipe which could ignite. Maybe an inert gas purge is possible? Cold methods like epoxy sealers mentioned earlier will be much safer. They may eventually loosen and leak again but then epoxy can be used again.
What I am really wondering is are the leaks in places other than joints?
If so, then maybe the leaks are just the beginning of the problems. If caused by internal corrosion then replacing the affected piping system may be the best answer, especially if the system is only 3 years old. Is vibration causing joints to open up?
Are you being asked to guarantee the work? I wouldn't want to from what you described so far.
CHGuilford
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