Process and Instrumentation Diagram
The Process and Instrumentation diagram gives details of all piping, including valves (automated and manual), by-pass lines,
pipe sizes, sample points, etc.
In addition, all instrumentation is covered in the P&ID of a process plant. Operating parameters,
flow rate, pressure drop, etc along with capacities of the process equipment are shown in the P&IDs.
P&IDs take the conceptual aspects of the PFD and expand them by adding the following ingredients:
Detailed symbols.
Detailed equipment information.
Equipment order and process sequence.
Process and utility piping.
Process flow direction.
Major and minor by-pass line.
Line numbers, pipe specifications and pipe size.
Isolation and shutoff valves.
Vents and drains.
Safety relief valves.
Instrumentation.
Control loops.
Types of process component connection.
Vendor and Contractor interfaces.
Skid and package interfaces.
Design requirement for hazardous operations.
Types of P&ID's:
1. Process Unit P&ID's: P&ID's of a particular unit such as a compressor, process plant, etc unit are called Process Unit P&ID's
2. Utility P&ID's: P&ID's of utilities such as instrument air, cooling water tower, chilled water system and boiler,etc are called Utility P&ID's.
3. Distribution P&ID's: P&ID's of main header distribution network shown geographically are called Distribution P&ID's. It can be for utility distribution as well as for process distribution.
4. Packaged Unit P&ID's: P&ID's provided by the original equipment manufacturer for a packaged unit e.g. Sulphur palletization unit etc. are called Packaged Unit P&ID's.
5. Legend P&ID's: P&ID's containing general notes, symbols, nomenclature, drains and piping details are called legend P&ID's.
General:
The size, service, line number, Piping Material Specification, type of tracing and whether insulated shall be indicated for each line on the P&ID's. Where lines leave/enter a P&ID the destination/origin equipment tag shall be marked.
If any special attention in piping layout and design is required, special notes shall be drafted on the P&ID's.
Other notes to clarify the P&ID's shall be added as required. For example, Flare line isolation valve should be installed with stem in horizontal plane to avoid free fall of gate and blockage of flare system.
