If the pipe is buried do not use fiber glass insulation as it will soak up the moisture in the soil and be worthless.
For the length of pipe you have then buy the insulation in preformed shapes and have it put on by a insulation contractor at the site.
I might add that for plant work I use either foamglas for cold or buried lines and calcium silicate for hot above grade lines. For long, buried pipelines, I use something else which has to be shop applied.
The only time I use fiber glass insulation in plant work is for noise attenuation reasons.
Finally, corrosion specialists hate PE coating as they regard it as inferior. The most common coating is FBE and can be put on (or arranged) by your pipe supplier. FBE also has a much higher operating temp than PE.