P&ID in thermal oil circuits



The PID name comes from the English, Piping and Instrumentation Diagram. It is also sometimes designated as P&ID. In practice it is the process diagram which presents schematically the flow of fluids in pipes and equipment, as well as the associated control instrumentation.

It is an essential tool, from which will depend largely the correct operation of the installation. On many occasions, this tool also serves to define the scope of supply. So, the battery limits that determine the responsibility and the scope of each company involved (if it is the case).


A correct PID is absolutely transcendental in thermal oil circuits to ensure safety, efficiency and reliability of the entire heating process. It is the starting point from which all equipment will be dimensioned, at both thermodynamic and hydraulic level.

The connection of equipment in series or in parallel, the presence of collectors, the proper degassing of circuit, the atmospheric or pressurized arrangement of the expansion tank, the required accuracy in the temperature control of the heat consumer equipment, and many other decisions, should be involved in designing of the PID.

In Pirobloc we are specialist in advice and design of PID’s for thermal oil circuits. We have the experience and computer means to calculate fully hydraulic and thermodynamic variables to ensure that the thermal fluid heat efficiently and safely all consumers.

This involves the pressure drop calculation of all the equipment involved in the circuit, their certain flow, delta T or temperature difference of generator equipment or consumers, etc. etc. In this way and from these calculations, the primary and / or secondary suitable pumps, pipe diameters, valves, recirculation groups and other elements will be selected.


The following images are examples of possible thermal oil PID. These diagrams correspond to real projects where the PID has been agreed with our customers. Logically, there are multiple possibilities for each case, and it is very important the communication and agreement between the various companies involved in the PID of the thermal oil circuit.

PID 2 heaters and 3 pumps

Download this example in PDF here.

P&ID base

Download this example in PDF here.