how i can use autoCad for piping and instrument diagrames???
Are you currently using normal AutoCAD or AutoCAD Plant3D?
AutoCAD Plant 3D already have your components created for you and is much easier to use if you doing piping. BUt in your case you basically need to create your own library. So you would create your components, convert them into blocks (Normal create block command), then in your toolpalette you will create a custom toolpalette and drag and drop these blocks into the toolpalette. So you can reuse these blocks in any drawing. And just make sure you create the appropriate layers for Piping & equipment.
The best way to get accurate help is to provide detailed information about your question. For example, you can post two images and ask: "I have a floor plan as shown in Figure 1. How can I create a diagram as in Figure 2 based on the floor plan?"
Its not that difficult to create diagramming drawings. Lets say you take 2 Days to create all your components and you have placed them in your desing centre and toolpalette. Then they will ALWAYS be there. You can save a backup of this toolpalette, so IF your computer crashes or you upgrade your software you still have your toolpalette.
Yes the P&ID side is better to use (like I said in my previous post) BUT it doesnt necessary mean you cannot to diagrams in AutoCAD at all. If you set your Grid & Snap settings and you have your components. You have a work around with the program that is given to you, unless you want another program.