[raghav1826]

Normally we are using pipe line underground how much length should I give ex for levels I.E, El,

[speedball1]

Normally we are using pipe line underground how much length should i give ex for levels I.E, El,

This has just got to be a classroom question. The invert of a sewer pipe is the surface of the bottom arc, (the bottom of the pipe) within which the liquid flows. The invert elevation is the elevation of the lowest part of that arc.
I would not apply the term to a pressure pipe such as a water main.
Since for a pipe to flow by gravity the invert must be sloped (neglecting the constant injection of water at head) the term invert elevation applies to one point in thelength of the pipe. Invert level implies an equal elevation surface or line, something that shouldn't exist in normal drainage. If that doesn't answer your question then be more explicit in the application. Cheers, Tom