Chemical Processing - January 2008 - (Page 34) M any plants rely on outdated process control systems — ranging from panel-based pneumatic controllers to Distributed Control Systems (DCS) installed in the 1980s — and now need to consider updating them. However, new technology for its own sake can’t justify capital spending — instead, it’s important for you to find compelling economic reasons for modernization. Using obsolescence for justification isn’t easy. While maintenance costs probably are rising and spare parts may be getting scarce and expensive, true maintenance savings normally aren’t large enough to justify the capital investment. Obsolescence is a viable approach only if you can show an increasing risk of control equipment failure shutting down a critical process. Establishing the risk factor becomes the challenge. It’s difficult to convince management that a system is about to fail when it has no history of failures. Predicting failure is a tough task. Mean Time Between Failure (MTBF) data for older, especially obsolete, equipment are hard to obtain. Plus, MTBF data normally are component-based, not system-based — making it hard to use these data to estimate control system life because a control system consists of multiple components. Fortunately, modernization can provide considerable financial benefits and thus significant incentives for a project. Whether these benefits will suffice to justify an upgrade, of course, depends on the company’s capital-spending payback policy. Some firms demand a one-year-or-less payback, others allow two-to-three-year paybacks, while a few factor in reduced risk of system failure in determining an acceptable period. Past financial failures Unfortunately, many control-system modernization projects haven’t provided the economic benefits that were initially expected. While engineering is happy to have the newest technology to implement and operations personnel view the process as easier to run, management may see the new system as a financial failure. Several factors can contribute to an automation upgrade project not bringing the expected economic value: • The process control system was chosen based on www.chemicalprocessing.com 34 • January 2008 http://www.chemicalprocessing.com
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