Closed cell urethane is one of the best insulations for this purpose with a k=.14 or R=7/in. It will resist water infiltration thru condensation or jacket compromise. If the pipe is buried, most engineers would specifiy that it be pre-insulated in a water proof insulation jacket and the world...
What are you trying to accomplish with the insulation? Freeze protection? Personell safety? Reduced BTU loss? Frost free exterior skin?
The insulation industry uses the 3Eplus program to calculate insulation needed for various applications. I'll bet you'll need betwee 2" and 2-1/2" of a...
