Piping and Instrumentation Diagrams P&IDs are essential in the field of engineering, particularly in industries like chemical, oil and gas, pharmaceuticals, and manufacturing. These diagrams serve as a blueprint for the design, construction, and operation of systems that involve piping, instruments, and control systems. They illustrate the interconnection of various components in a process system, such as pipes, valves, instruments, and other equipment, in a clear, standardized manner. To read and create P&IDs effectively, engineers must understand the key symbols used within these diagrams. Here are 44 of the most crucial P&ID symbols that are commonly used in engineering projects. Piping is represented with a simple line, but various styles indicate different types of pipes, such as fluid, gas, or steam pipelines. Thicker lines may represent primary process lines, while thinner lines may represent secondary or auxiliary lines. Valves are crucial for regulating the flow of fluids or gases. There are different valve symbols for gate valves, ball valves, check valves, and pressure relief valves.
These symbols often include arrows to indicate the flow direction and might feature a unique handle or actuator for specific valve types. Instrumentation symbols are used to show the types of instruments involved in measuring, controlling, and regulating the system. Pressure transmitters, temperature gauges, and flow meters each have a distinct symbol. For instance, a pressure gauge might be represented by a circle with a P inside, while a flow meter could be shown with a box containing an F and arrows for direction. Control valves are critical for managing the flow rate of fluids in the system. These valves are typically represented with a diamond shape and are often connected to controllers and sensors, such as a positioner, to regulate the system’s operation automatically. Pumps are represented by a circle with a P inside. These symbols may be further classified into centrifugal pumps, reciprocating pumps, or diaphragm pumps based on the type of motion used to move the fluid.
Compressors, often used in gas or air systems, are shown with p&id symbols that usually include a cylinder or a spiral. These symbols may also include specific indicators for compressor types, such as centrifugal or reciprocating. Heat exchangers are vital for transferring heat between fluids without mixing them. The symbol for a heat exchanger typically shows a pair of parallel lines or a series of lines to indicate the heat transfer process. Tanks and vessels are depicted as horizontal or vertical rectangles or cylinders. These can include storage tanks, reactors, and separators, each with specific notations to show the function or internal conditions, such as temperature or pressure. Level measurement devices such as float gauges or level transmitters are represented by a line with a box or specific shapes indicating the device’s function. Arrows might indicate whether the device is sensing the level from the top or bottom. Symbols for filters and strainers represent equipment used for separating particles from a fluid.