pressure testing used kegs

[Movinfr8]

just picked up 5 used kegs $15 each. I am pressure testing them now, I put 50 psi (compressed air) in each yesterday at about 2p.m. and at 9:15 they have between 45 and 47 psi. is there a standard leak down rate where they should be rebuilt?
What else should I do to a new used keg?
thanks,
Norm

 

[Bobby_M]

Two things; that amount of pressure differential could easily be attributed to minor temperature changes. Testing at that pressure is unrealistic as beer will be at about 12 PSI. Bring the pressure down below 20 and spray some soapy water on the top of the keg and look for bubbles.