I had to install a new kitchen faucet. After I removed the old faucet,
the galvanized steel nipples were too damaged from corrosion so I
removed them. Then I put in new nipples, using teflon paste. How tight
am I supposed to tighten them? Am I supposed to keep turning until it's
very hard to turn or what? So far I only tighted them enough to not
leak, because I didn't want to damage the old galvanized steel pipes,
which are very old. The amount of force I had to use was not very much
(using a vice grip).

Somewhere between a gentle nudge and full force. You should not put
all your weight into them. If you have them to where they don't leak,
give it a pinch more, and that should do it.

GreatArtist wrote:
I had to install a new kitchen faucet. After I removed the old faucet,
the galvanized steel nipples were too damaged from corrosion so I
removed them. Then I put in new nipples, using teflon paste. How tight
am I supposed to tighten them? Am I supposed to keep turning until it's
very hard to turn or what? So far I only tighted them enough to not
leak, because I didn't want to damage the old galvanized steel pipes,
which are very old. The amount of force I had to use was not very much
(using a vice grip).

I was once told to tighten 1" black pipe to 50 ft-lb. I believe that
puts an "upper limit" on how tight you should make the nipple.

Hope this helps,
William