K Controls has supplied a major UK refinery with 160 stainless steel position monitors for retrofitting to a variety of different rotary and linear valve actuators. This particular plant removes acid from petrol in order to make it suitable for vehicle use. The triplicated safety systems that have been used offshore for many years are now gradually being introduced into refineries as safety systems are upgraded to meet the latest regulations. The K Controls position monitors will be used in conjunction with special Triconex PLC’s from Invensys that implement a two out of three voting system prior to implementing any control changes. Each position monitor contains both end of travel limit switches and a 4-20mA transmitter complete with the HART® protocol that allows it to be remotely calibrated. This enables the PLC to monitor valve and actuator performance throughout valve travel. The valves are being partially stroked to an agreed schedule and in accordance with planned maintenance procedures. The PLC monitors the movement and issues an alarm if the time taken exceeds a pre-defined limit. Valve movement is also graphically displayed and any irregular patterns are investigated. This process ensures the valves are in good working order and ready to react if a programmed shut down of the system is required in the event of an emergency. K Controls was able to provide the contractor with SIL (safety integrity level) or life data for all the components used in the position monitor, and the product was engineered to enable the PLC to perform short circuit and line break monitoring. As the units are operating in a coastal environment, stainless steel IP67 enclosures were required together with hermetically sealed switches. K Controls also provided highly visible polycarbonate position indicators on the rotary units and engineered and supplied all the valve actuator mounting kits needed for the retrofit. The units are fully ATEX certified for use in intrinsically safe systems but where the necessary safety interfaces were not available, versions are certified flameproof Exd.
