1)What does "Piping plan" mean related to process plant . Is it a drawing.... if yes what is included in it ...........

2) is following sequence of drawing correct for piping dept.
i) PFD (input for piping dept)
ii) P&ID (input of piping dept)
iii) plot plan
iv) Piping layout (output of piping dept)
v) Piping isometrics (output of piping dept)
vi) piping plan (output of piping dept)

..........?

It's a plan drawing of piping, done by a piping designer.

You ask some very basic questions ..... do you have nobody in your organisation who can answer ?

Engr mech, from your questions you seem to be a young enthusiastic engineer at the beginning of your career. It is very good to be inquisitive and keen, however it is also important to try and research as much as possible on your own before posting on sites which may not be relevant to your queries.

Most of your queries are general piping engineering, and design overview questions, not stress analysis or technical piping queries. These questions do not require to be answered on a forum which is focussed more towards technical queries and stress analysis modelling techniques.

I see that you are located in Australia (I used to work there), most companies there have good engineering departments with good depth of experience. Your questions are the same ones I had when I started as an engineer, however I was able to refer to my supervisor / colleagues for assistance where I was unable to teach myself.

I suggest you approach your supervisor with your queries. That way you will learn to learn on the job, and also you will give your supervisor an indication of your level of development.