P I diagrams

The process and instrumentation (P I) diagram provides a graphical representation of the control configuration for the process. The P I diagrams illustrate the measurement devices that provide inputs to the control strategy, the actuators that will implement the results of the control calculations, and the function blocks that provide the control logic. 

The symbology for drawing P I diagrams generally follows standards developed by one of the following organizations ... 

Figure 8-47 presents a P I diagram for a simple temperature control loop that adheres to the ISA symbology. The measurement... 

Information normally excluded from P I diagrams includes electrical wiring (normally separate electrical diagrams must be consulted), nonprocess equipment (e.g., hoist, support structures, foundations, etc.) and scale drawings of individual components. 

Does this concept of a P-i diagram as a measure of response or damage work for complex structures, as well as simple ones ... 

Figure 16. P -I Diagram for Blast Loaded Rigid-Plastic System.

Figure 18. Illustration of Overlays to a P-I Diagram. Incident (Side-On) Overpressure and Impulse from Pentolite Spheres. (Reprinted with permission from ref. 15. Copyright 1983 Elsevier Science.)...

Other possible preliminary safety analysis methods are concept safety review (CSR), critical examination of system safety (CE), concept hazard analysis (CHA), preliminary consequence analysis (PCA) and preliminary hazard analysis (PHA) (Wells et al., 1993). These methods are meant to be carried out from the time of the concept safety review until such time as reasonably firm process flow diagrams or early P I diagrams are available. 

Figure 23-1 shows the hazards identification and risk assessment procedure. The procedure begins with a complete description of the process. This includes detailed PFD and P I diagrams, complete specifications on all equipment, maintenance records, operating procedures, and so forth. A hazard identification procedure is then selected (see Haz-ard Analysis subsection) to identify the hazards and their nature. This is followed by identification of all potential event sequences and potential incidents (scenarios) that can result in loss of control of energy or material. Next is an evaluation of both the consequences and the probability. The consequences are estimated by using source models (to describe the... 

P I diagrams contain four important pieces of information, namely, all vessels, valves and piping, along with a brief description and identifying specifications of each all sensors, instruments and control devices, along with a brief description of each the control logic used in the process and, finally, additional references where more detailed information can be obtained. 

Piping normally is denoted by solid lines. Piping lines on the P I diagram should be accompanied by the following identifying information ... 

These are P I diagrams for individual utilities such as steam, steam condensate, cooling water, heat transfer media in general,... 

Rather less freedom is allowed in the construction of mechanical flowsheets. The relative elevations and sizes of equipment are preserved as much as possible, but all pumps usually arc shown at the same level near the bottom of the drawing. Tabulations of instrumentation symbols or of control valve sizes or of relief valve sizes also often appear on P I diagrams. Engineering offices have elaborate checklists of information that should be included on the flowsheet, but such information is beyond the scope here. 

Fig. 2.30. Simplified P. I diagram of liquid nitrogen. 1, Chamber and shelves 2, condenser 3, silicone oil circuit 4, heater 5, heat exchanger.

Figure 2 Detailed P I diagram of feed-pipe to acetone distillation column...

Figure 1 P I Diagram of the Experimental System for both Types of Operating Modes...

The process flow diagram, or PP D, is a pictorial description of the process. It git es the basic processing scheme, the basic control concept, and the process information froiti which equipment can be specified and designed. It provides the basis for the det elopment of the P I diagram and also serves as a guide for the phmt operator. The process flow diagram usually includes... 

Process diagrams are a necessary part of a plant. Flow and P I diagrams aid the process engineer in understanding, controlling, and troubleshooting the process. They also provide valuable information about the process in the event of an emergency. 

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