Enhancing piping, instrumentation diagrams to fit your needs

Process overview documents don’t always include everything you may need for a project, so don’t be afraid to add your own grubby little sketches.


When I start work on a project, the first thing I do is get an understanding of the process that will be controlled. Piping and instrumentation diagrams (P&IDs) are a useful resource, but they are multi-purpose documents. They may include piping codes, vessel specifications, and construction notes. A process usually covers multiple P&IDs.

If the existing process is already controlled by a distributed control system (DCS) or programmable logic controller (PLC), the existing operator interface displays are also useful references. A process usually requires multiple displays to show all of its components. If there are few displays, or if there are good process overview displays, I can use them for my purposes as they are.

More often, the kind of process overview I want does not exist. In that case, I create my own grubby little sketch. What I need is a drawing that shows the major pieces of process equipment and process flows. I can then add the main process control functions. This kind of drawing is particularly helpful for understanding complex control strategies. Given time, I prefer to create an electronic drawing that is more orderly and legible than my initial grubby little sketch.

For a project, it’s useful to have one drawing that documents the existing controls and another drawing that shows the proposed control strategies. These clarify the changes that must be made in order to implement the new strategies. They are also useful for explaining the plans to the stakeholders. It’s often easier to show a drawing of what exists along with a drawing of what will be, rather than to try to describe the changes in words.

Recently, I worked on a project that provided the controls scope in the form of detailed functional descriptions. The project was changing process flow paths along with changing control strategies. The functional spec document included a drawing of the new flow paths, but the drawing did not show any instruments. I printed out a copy and added the control equipment as I went through the functional specification, later cross checking the results with the P&IDs.

When I met with the stakeholders, I had my grubby little sketch with me for reference. After I used it to ask questions and point out a few issues, one of the stakeholders said, “I want a copy of that!” He made copies for the rest of the team, and we continued to use them during the discussions. The P&IDs for that project were torturously arranged, so having an overview was very handy.

My colleagues on that project team would probably have preferred a tidy, electronically created overview, without my editorial comments. Having the information, however, trumped the messiness of the sketch.

What experiences have you had with using overview drawings to plan strategy changes or to communicate those plans to a larger team? Have you found better ways to communicate control strategy information?

This post was written by MayAnn Stroup. MayAnn is a senior engineer at MAVERICK Technologies, a leading automation solutions provider offering industrial automation, strategic manufacturing, and enterprise integration services for the process industries. MAVERICK delivers expertise and consulting in a wide variety of areas including industrial automation controls, distributed control systems, manufacturing execution systems, operational strategy, business process optimization and more.

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