Compressor Treatment - Anti-Rust or Inhibitor?

As long as you keep the water drained it is not necessary.

On the other hand, if that water was allowed to stand inside the pressure vessel for any length of time, it could have compromised it's structural integrity. When pressurizing, stand clear just in case.

Yes you need to treat it in order reduce the rate of corrosion on your steel vessel.First drain the vessel before opening the inspection/access door,to atmospheric pressure.Open inspection door,Remove scales and rust by chipping or sandblasting method.Clean the vessel, non destructive test to check for cracks,apply the primer paint coating,prefer by aid of spray gun.

Remember Safety precautions-: PPE (Personal Protective Equipment) and sufficient ventilation are essential during exercise.

You didn't say how large or how old the vessel. Post #2 is a good answer for vessels large enough to have a clean-out access, but many smaller compressor tanks have no such opening. Part of the brown color may be due to oil in the water in addition to rust. The safety precautions are always good. Every permanently mounted compressor should be operated in a location where people are not normally nearby, so that in the event of a rupture or other failure, the probability of injury is minimized.

I suspect that the majority of compressor tanks are not drained as frequently as they should be, yet compressor tank ruptures are rare (to my knowledge), so I think post #1 is probably valid.

Preventing accumulation of water in the cylinder is best solution,regular drain is essential a automatic water drain device plus manual drain plug will suit the purpose

If the water is brown it would indicate that the inside is rusty & unless you know the service history you've no way of knowing how bad, most pressure vessels I've owned when they're drained the liquid is milky white, so be careful or it could fail.

Bazzer

Milky like liquid its indication of lube oil ingress from air compressor lubricating oil or presence lube oil in the atmosphere sucked by air copressor carried to air vessels.Water formation depend on humidity condition,water + Oil = milky liquid.In extreme cases where steel corrosion has reached a higher stage a NDT (a non destructve test) and hydraulic test are essential depending on nature of job and maximum pressure required.

if possible i'd suggest an internal visual inspection, maybe visual with a video inspection, to assess if there is an internal corrosion.

S

corrosion & rust protection