EVERY PICTURE TELLS A STORY…DON’T IT?

Every picture tells a story... don't it?

("Every Picture Tells a Story," Rod Stewart/Ron Wood, 1971)

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PIPING AND INSTRUMENTATION DIAGRAMS (P&IDs)

How is it possible that every temperature indicator in a process plant is exactly placed to be useful for some purpose?

No PTOA Reader or Student would build a house without a design plan. Likewise, long before a backhoe started preparing the foundation of a processing plant, many types of plant design paperwork had been discussed over and over.

One of the design documents that Process Operators use is a Piping and Instrumentation Drawing (P&ID).

Prior to construction beginning, the Plant Owner agreed to pay the construction contractor for each piece of hardware and software that went into building the plant. During the P&ID review sessions, the Plant Owner's representatives verified that each hardware and software investment had a purpose related to safe and efficient operations, enhanced production, and ease of maintenance intervals.

If a TI wasn't needed, it would have been removed from the P&ID. In fact, a conversation justifying its need and purpose took place.

This person is a "Control Board Operator." The career path to becoming a "Control Board Operator" is usually 5 years at a minimum.

Experienced Process Operators and Control Board Operators also attended the P&ID review meetings.

The Process Operators had years of experience turning real valves and operating the real pumps and compressors that were represented as symbols on the P&ID.

The Control Board Operators had years of experience being responsible for the continued safe and efficient operation of multimillion dollar processes.

The input from the Process Operators and Control Board Operators was carefully heeded during the P&ID reviews.

WHAT DOES A REAL TI LOOK LIKE
ON A P&ID SCHEMATIC?

The nearby schematic is part of a real P&ID.

The picture shows two twin vessels. The abbreviation for "vessel" is a capital "V."

The left side vessel has been labelled "V200A" and inside of it is "Carbon Bed A."

The right side vessel is labelled "V200B" and inside of it is "Carbon Bed B."

The X pattern on the vessel bodies represents the carbon beds that are packed inside.

There is a small carbon filter in the dome of this Brita® water filter that removes contaminants from drinking water

Do you have a Brita® carbon filter on your household water faucet or in a Brita® pitcher?

V200A and V200B work a lot like a Brita® carbon filter to remove contaminants from the process fluid. The X pattern on the vessel bodies represents the carbon beds that are packed inside.

Hey! PTOA Readers and Students that look closer will notice black,hand-drawn arrows that point to three TIs on each of the carbon beds.

From the top to the bottom, the three TIs on V200A have the respective tag names TI 3A, TI 3B, and TI 3C.

From the top to the bottom, the three TIs on V200B have the respective tag names TI 3D, TI 3E, and TI 3F.

In real life, TI 3C or TI 3F might look like this TI which is also at the bottom of a real process vessel:

This real TI is on the bottom of a real vessel. This TI could be either TI 3C or TI 3F in the P&ID at the top of this page

The three TIs appear to be drawn equally and intentionally spaced apart between the top and bottom of each carbon bed. PTOA Readers and Students can conclude from the observation of three equally-spaced TIs on each carbon bed that …

There must be something about carbon interacting with the process fluid that requires monitoring the temperature of the entire carbon bed, from top to bottom.

HOW TIs 3A THROUGH 3F WERE DRAWN

All six of the TIs were drawn by first making an empty circle.

Then the letters "TI" were drawn inside the circle to indicate that the circle represented a Temperature Indicator.

Then the number of each TI was added to the correct circle.

The duo parts of identifying what kind of instrument the circle represents (a TI in this example) and the number of the instrument (3A through 3F in this example) is called the "tag name."

Then a line attaching the circle to the vessel was drawn to give the reader of the P&ID an idea where the TI could be found on the real vessel.

ALL PROCESS OPERATORS MUST LEARN TO DECODE P&IDs

All PTOA Readers and Students will eventually be able to thoroughly understand the P&ID in the top photo.

Understanding how to interpret P&IDs and PFDs is an essential job skill required by all Process Operators, Control Board Operators, and most Maintenance and Auxiliary facility personnel. "Reading P&IDs" is like being a detective and decoding a message.

The best way to get familiar with any processing plant is to print out a set of P&IDs and walk the lines of the facility while referring to the diagram. Using a yellow highlighter to draw over the process lines that have been studied is very helpful; the lines that are not yet highlighted remain to be walked out.

The complex web of pipes and pumps and vessels and towers will not seem intimidating after walking out the P&ID. Promise!

WHERE DO THE P&ID SYMBOLS COME FROM?

As the use of automation technology began to increase in process industries, the need to standardize construction design diagrams became apparent.

The original part of the plant may have been built by a contractor that used certain flow scheme symbols and other parts of the plant built during expansion projects by different contractors might use a slightly different set of symbols.

The Instrument Society of America (ISA) began the process of standardization in the mid 1940s. The society grew in influence and world-wide membership and in 2008 adopted a name change to the International Society of Automation.

Non-standard ISA symbols can still be found in the original documentation of older facilities and internationally. For this reason, a symbol key will always be the first page of a P&ID and can be used to facilitate P&ID interpretation of unknown symbols.

The ISA continues to be the official authority for keeping the ISA symbol standard current with new technologies.

A link to the ISA website in general and specifically the ISA Standard 5.1 "Instrumentation Symbols and Identification" is below.

The link is provided for awareness purposes only. and to credit the ISA for the important work they accomplish.

Your Mentor DOES NOT recommend purchasing the standard. Relevant ISA symbols will be shown in PTOA segments. The link is below:

ISA 2009 Instrument Symbol Standard

I MEAN THIS AND NOT THAT

Be aware that some well-meaning people (and maybe even your supervisor) refer to a P&ID as a "Process and Instrumentation Diagram."

Don't correct him/her. Although the phrase is gaining in acceptance, PTOA Readers and Students should stick with "Piping and Instrumentation Diagram" to eliminate confusion with Process Flow Diagrams (PFDs).

PFDs and PIDs are distinctly useful schematics used by Process Operators and most everyone else working at a production plant.

Take Home Messages: Every Process Operator must be fluent in reading and interpreting Piping and Instrumentation Diagrams (P&IDs) and Process Flow Diagrams (PFDs).

The symbols used in a P&ID and the nomenclature for instrument tag names are determined and updated by the International Society of Automation (ISA).

The ISA symbol for a local Temperature Indicator is a blank circle with the tag name inside the circle.

Older facilities may still have P&IDs with non-standard nomenclature and symbols. The cover page of each P&ID will have a symbol key to help with P&ID interpretation.

Performing a P&ID "walk out" is a great way to learn a processing plant.

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