It depends on where you are placing the pipe. The material of the pipe itself doesn't usually dictate the compaction.
You should first see if the local jurisdiction has requirements that need to be followed, i.e county road & bridge department, state highway department, etc. If the pipeline is going through an open field with no improvements or planned improvements 80% is usually OK. If it is in the shoulder of a road but outside of the roadway prism 90%, if it is under a road, driveway or other area where there will be some type of improvement on top or possibly influenced by the pipeline 95% is usually recommended. The percentages are modified proctor.
