November 2009

Insight into real-world process control

By Nagappan Muthiah

If you plan on working for a processing company or an Engineering, Procurement, and Construction company, the key to succeed in the world of process control is to understand the following rules and constraints.

1. "Your primary goal is to develop profitable solutions for the company."

The main motive is to develop viable, profitable solutions. Hence, the need for any advancement, enhancement, or replacement of an existing system has to make economic sense. One must justify the time and money involved in their execution and long-term maintenance. Economic justification is an important factor in gaining acceptance of your ideas. 

2. "If it's not broken, then don't fix it."

In the process control industry, there is much resistance to update functioning systems. Even though there may be several technical advancements in implementing process control by utilizing newer software and hardware, most of the industries do not embrace them immediately. They run their plant with technologies older than 10 years or even 20 years. Any changes to the core control systems require a large amount of money and retraining for the maintenance and operations staff. An upgrade may also involve extensive plant shutdowns and add new risks. In most cases, it is difficult to justify this cost; and hence, the industries stick to their old existing technology for as long as they can. You may have to train yourself to work with this constraint. As an exercise, justify (in dollars) why you want to upgrade from Windows XP to Vista on your personal laptop.

3. "Perfect linear systems don't exist."

The above-mentioned concept applies for replacements of field instruments as well. For instance, we may have a 10-year-old control valve in the field that does not respond linearly to the PID output signal. It is very likely the cost to design, go through manufacturing delay, manufacture, and install the new valve is going to be much higher as compared to using the same old valve and maintaining it meticulously so it gives satisfactory performance. In the academic world, design logic assumes all the instruments will respond in a linear fashion. In the real world, one should design continuously to maintain the process control system to compensate for the non-linear action of the instruments and other devices out in the field.

4. "K.I.S.S. - Keep it simple and safe"

We can use our advanced control knowledge and develop the most efficient control algorithm. However, if this logic is not easy to understand and maintain, it is highly likely after sometime, someone will put this algorithm in "Bypass" mode.

A process plant is always running, and the plant is making product 24 hours a day, seven days a week. Hence, the Advanced Process Control logic should not only be efficient, but it should also be highly robust so it can handle the various disturbances and non-linearity in the process instruments and process itself. 

5. "Team Player: The most important skill set"

In order to succeed in your career, you will have to be a great team player. Understand who your associates are, what they value, what they want, what constraints are on them. You need their advice, direction, insight, and partnership. Value them. Further, communication, written and oral, is essential to being a viable asset to the company and successful team player.

ABOUT THE AUTHOR

Nagappan Muthiah (muthu@contechnet.com) is a member of ISA and has five years of experience performing control systems expansion and upgrade projects for oil and gas companies. He has a master's degree in Control Systems Engineering from Oklahoma State University.