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How to Read P&ID Drawings
Mar 28, 2019

Reading P&ID is a difficult task for those who start their career in Oil &Gas and similar Chemical Process Industries. Piping and instrumentation diagram is also known as Process engineering flow scheme which is PEFS.P&ID is more complex than of PFD and includes lots of details.

 1. What is P&ID?

P&ID is a graphical representation of the actual process plant using various symbols that represent actual equipment. As said earlier it is complex than PFD. A single PFD can have multiple P&ID. This means if some system is shown on single PFD, to show the same system on P&ID, it may require multiple P&ID sheets. It is one of the main deliverables of FEED. That is front-end engineering and design. It is used during the entire life-cycle of the plant. That means during pre-EPC, EPC and operation.


2. Use of P&ID/PEFS During Pre- EPC & EPC Phase

P&ID is used to derive Project capital cost estimate. It is also used to develop EPC contract specification. Plot plant is developed considering various inputs from P&ID and physical site location. During the EPC phase, P&ID is used to develop the individual unit layout. It used to identify hazardous areas classification, preparing data sheets of equipment, valves, and instrument. P&ID are used to develop the piping layout and preparing bulk material take-off for piping, electrical, instrumentation and civil. It is key documents for various review such as HAZOP, SIL and operability review. During Operation, you have to maintain P&ID in such a condition that it will show actual plant conditions at any time. It should be updated when any physical change is made so that the unit will remain compliant with codes, standards, and specification, and can be operated safely under the defined process conditions. P&IDs are used to train operators and engineers before they start work in the plant.


3.  What information does P&ID provide?

  • All the equipment, including installed spares, and associated piping including drain and vent line.

  • Insulation or jacketing requirements.

  • Instrumentation

  • Heat tracing and insulation detail

  • Information about utilities

  • Piping components including their size, class and tag Number

  • Information required for design, construction, and operation such as

  • A slope of the line

  • Minimum and maximum distance from the equipment or instruments

  • Minimum straight lengths after instruments

4.  What information does p&id provide?

  • Process conditions and physical data

  • Operating conditions

  • Stream flow details

  • Equipment locations

  • Pipe routing, length, and fittings

  • Support and structural details are also not included in p&id

5. How to read P&ID symbols