P&IDs play very important roles in plant maintenance and modification in that they demonstrate the physical sequence of equipment and system as well as how they all connect. During the Design stage they provide the basis for the development of system control schemes, allowing for further safety and operational investigations like HAZOP (Hazards and Operability Study).
Piping on a piping and instrumentation diagram(P&ID) is indicated by:
- Usage: For example, process, drain, nitrogen, blow down, etc.
- Line Number: The identification number of the line on the plant.
- Size: Usually in inches.
- Piping Class: The piping specification, both material and pressure rating
- The insulation class
The specification is usually given using American standards e.g. American Society of Mechanical Engineers (ASME) or American Petroleum Institute (API). Each installation uses slightly different methods to do this but the end result is the same. A typical example is given below:
3” - Signifies the line size in inches, i.e the line size here is 3 inches
P - Signifies fluid service
12007 – 12 here Signifies unit or facility number while 007 denotes the serial number
A11A - denotes the piping service class
H - denotes the insulation type
30 - denotes the insulation thickness
If we further break the piping service class A11A down, we see that:
A - denotes the flange rating
11 - denotes the piping material
A - a suffix qualifying the piping material
The designation here may be a little different from the ones you may come across but the basic components below will always be part of the piping designation in a piping and instrumentation diagram:
- Line number
- Piping class and
- Insulation class