Piping & Instrumentation Diagram Series


FlowLines on P&ID

All Flow lines and Interconnections should be shown on P&ID’s. Every line should show direction of flow, and be labeled to show area of project, conveyed fluid, line size, piping material or specification code number (company code), and number of the line.

Line Number example: 74-BZ-6-412-23 may denote the 23rd line in area 74, a 6-inch pipe to company specification 412. ‘BZ’ identifies the conveyed fluid. This type of full designation for a flow line need not be used, provided identification is adequate.

Piping drawings use the line numbering of the P&ID, and the following points apply to piping drawings as well as P&ID’s

  • For a system of lines conveying the same fluid, allocate sequential numbers to lines, begining with ‘1’ for each system
  • For continuous line, retain the same number of line (such as 23 in example) as the line goes thru valves, strainers, small filters, traps, venturis, orifice flanges and small equipment generally-unless the line changes size
  • Terminate the number of the line at a major item of equipment such as a tank, pressure vessel, mixer, or any equipment carrying an individual equipment number
  • Allocate new numbers to branches

As with the process flow diagram, directions of flow within the drawing are shown by solid arrows placed at every junction, and all corners except where changes of direction occur closely together. Corners should be square. The number of crossing should be kept minimal by good arrangement.

Process and service streams entering or leaving the process are noted by hollow arrows (Offpage Connectors)  with the name of the conveyed fluid written over the arrohead and the continuation sheet number within it. No process flow data will normally be shown on a P&ID.

Next time

Notes for lines, showing equipment and Special Items


Total Cad System Inc.

2 Responses to “Piping & Instrumentation Diagram Series”

  1. Pea Says:

    hi, please can you recommend a book for absolute beginners to AutoCad. i am a beginner & i am interested in learning autocad.


  2. Todd Rogers Says:

    Yes Pea, the best solution in my opinion is to watch youtube videos on AutoCAD.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: