Are you sure it was not a copper pipe with a male pipe adaptor sweat on?

Also refrigerant and A/C pipe ca and does have up to 300# psi and some
new refrigerant runs at over 400#. That is why you use sil-fos 15%
silver on the copper to copper. Copper to brass silver solder 40% silver
And as always nitrogen at 2psi must repeat M U S T be flowing thru the
system. If you have an a/c system being repaired for a leak or new
system being installed make dam sure nitrogen is purged thru the system
And if you see some one repairing your system with out nitrogen hooked
up then ask them to stop and do it right and keep the inside of the
system clean .