Thursday, February 5, 2015
What is a P&ID?
What is P&ID?
A P&ID or a piping and instrumentation diagram is nothing but a diagram which depicts all the pipe lines and instruments connecting various process equipment and vessels. Here in these diagrams we can see the pipe line size, service, material of construction and the line number from piping point of view. Also the number of valves and their type using for a particular project are finalized based on the P&ID. For different types of process equipment and fittings we use various symbols to differentiate their purpose. Certain operating conditions like temperature and pressure are also represented near critical areas like pressure safety valves. The above discussion revolves around the process engineering.
Coming to the instrumentation part, just think about how you will measure the flow, temperature, pressure etc., in a pipe line which is flowing at higher temperature and pressure. You can’t take a chance to measure all the parameters by your hand 24*7 and report to DCS (Distributed control system) that’s funny right. That is where you need the help of instruments like transmitters, indicators, recorders, alarms etc., if you want to know the process parameters in various places of the plant you need to mount these instruments at the respective areas. Some of them may be locally displaying instruments and some may send the parameter details to DCS. You need to show all the instruments in the P&ID with various symbols and notations for local, DCS instruments.
P&ID diagrams also embody the control mechanisms involved in the process. For example if a low level in a vessel should close the discharge line from that vessel, the level transmitter in that vessel should send a signal to the control valve in the vessel discharge line. This can be easily represented by the following drawing.
Another aspect of P&ID is the interlock representation. Interlocks are very critical and vital for the safe operation of the process plant. The open loops and closed loops look after the normal operation of the plant whereas the sequence and logic look after the emergency shutdown functions. These interlocks are also represented in the P&ID. For tutorials on P&ID development keep watching the site www.chemineering.blogspot.com.
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