What is mean by edge preparation in piping?

Answer 1

Most pipe doest come ready to weld, one has to "sand or brush' the area to be welded. Hence cleaned

Answer 2

The preparation needed depends on what type of pipe your dealing with and what your trying to do with the pipe. Most typically your talking about two welded joints of metal pipe that require the edge to be smoothed and beveled to be ready to accept the weld.