You'll probably have more problems keeping the insulation dry than you'll have with corrosion on the pipe itself. Earth provides rather good insulation, so in many places you can place it deep enough so that it won't freeze, or circulate a rather small amount of fluid within to maintain temperatures above freezing at all times.
If you use insulation, be sure to use one that is totally impermeable.
yes you're right.
but we know the galvanizing is the one of methods for prevention of corrosion, and we do a coating and wrapping on it.
i mean, we do coating twice. one galvanize, second wrapping. if this act is right or not?
Yes you can coat (wrap) galvanised pipe and it will buy you some extra life; however, you will still need to evaluate cathodic protection to support the coating over the long term. This consideration should then lead to the evaluation of whether you pay for the zinc as a coating and as the CP, or whether you can leave the zinc off the pipe and just have it as the CP!