Buried Pipeline vs Aboveground Pipeline

The circumstances are:

A/ you don't want to see it

B/ you want to see it

From my experience pipelines are always buried (for protection) until it becomes cost prohibitive to dig the trench (typically rocky areas). In all cases that I installed pipe above ground, it was simply cost driven.

You need cathodic protection for UG pipes and leaks cannot be seen but safe from mechanical damage.

Cathodic protection is not universally required for underground piping. It depends on the materials used and the intended design life. I have not heard of or designed any concrete, PVC, ductile iron, or HDPE piping systems with cathodic protection. In fact the only material I have seen with CP is steel.

Ductile iron uses zinc for cathodic protection, during manufacture they are spray coated (metalised) with zinc. Used along with a sacrificial anode any damage to the protective coating results in a zinc blister forming protecting the ductile.

This might be a difference in the norm between countries or perhaps a difference in pipe design criteria. I've never heard of such a thing here in the US.

ug piping requires wrapping and cathodic protection for steel pipes.

site physical feasible conditions,HSE stabdards also having affective role in differentiation between AG and UG

It is rate for drainage and sewage piping to be <...Above ground pipelines...>.