Plants Pit New Tools Against Corrosion

Real-time measurements lead to better uptime and other benefits.

By Seán Ottewell, Editor at Large

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Honeywell's latest offering, the OneWireless SmartCET range, transmits corrosion data wirelessly — a boon in areas of limited access where safety is an issue. The wireless mesh network makes adding more monitoring points easy. However, wired units still dominate, accounting for about 80% of corrosion monitor installations. "But I see a much greater growth for wireless in the future — perhaps 50/50 wireless-to-wired within five years," notes Srinivasan.

Another change he foresees is corrosion becoming more a part of plant operation and control rather than maintenance. "Online monitoring lets you integrate corrosion rate into integrity operating windows and support efficient, safe process boundary management. For example, a $2-billion refinery might spend $100 million on maintenance over its life. One way to cut down on this cost is to monitor corrosion in real time and make it part of online process control/management."

Going forward, all corrosion data will become part of the historian, he believes, enabling users to refine processes to give optimal performance. In fact, big customers such as Shell already are using such data in their online operating framework. They see deviations immediately and can adjust the process accordingly.

"We have closed the loop on correlating corrosion rates to factors that cause corrosion as the process happens. We are getting greater accuracy and a proactive response to a specific operational target. All this feeds into the need for improving safety, reliability and, most importantly, efficiency — as a foundation for maximizing profit," says Srinivasan.

NOT TREADING WATER
Two groups of major customers — large petrochemical plants and refineries that use inhibitors in their water supplies to prevent problems such as corrosion, biofouling and particulate buildup, and water-treatment-service vendors that must document whether corrosion is under control in cooling water circuits — have prompted developments at Pepperl+Fuchs, Twinsburg, Ohio.

The company has introduced CorrTran MV (Figure 2), which is aimed at the chemical and oil and gas markets, and CorrTran Aqua for cooling tower users. In addition, a wireless data logger called the CorrTran Electronic Coupon is due out in the first quarter of 2012. It is battery operated and requires no programming. Users simply remove it from the process after a specified period of time and access the data via an SD card.

Overall, these products aim to improve process-to-corrosion correlation. "This is important because it allows correlation of events that are not easy to understand. The traditional coupon is essentially a linear measure of mass-loss-through-lifetime of a system. CorrTran's strength is that it takes a reading every 20–30 minutes, or every four minutes for generalized corrosion applications. That means we can look at data with respect to the rest of the process, i.e., see which process upset (such as pump calling, flow rate change, etc.) caused the rate of corrosion to change. It also allows users to do some work in the inhibitor area," says Mike McElroy, business development manager.

At one chemical plant, CorrTran is used to monitor the boiler supplying steam to the entire site. Inhibitor in the water must be strictly controlled because if too much is deposited on the heat exchanger surfaces then their properties can change. "… This customer lost two to three heat exchangers over a three-year period because corrosion caused perforations in the heat exchanger tubes, which allowed process chemicals into the steam system. Since CorrTran was installed three years ago, this chemical manufacturer has not lost one heat exchanger. So there's been a real payback," says product manager Mike Mendicino.

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