Control valves and measurement instruments are critical pieces of equipment in industrial processes. Problems in them makes the rest of the process to suffer. Right targeted maintenance actions are crucial in maintaining adequate process performance. Known condition of control valves and instruments can be utilized in maintenance planning to focus actions to the devices most needing attention.
Traditional ways to diagnose control valves and instrumentation have been either by analyzing digital valve controller’s and instrument’s device information or by testing and analyzing with portable testing tools. Metso Flow Control Services introduces ValveTriage Service, a new way to evaluate the device condition and performance utilizing process information. This is especially tempting for plants not having modern digitalized device technology with associated systems or possibilities and resources for the portable testing.
Control systems are gathering real-time data from all corners of the plant. The data can be stored and used to analyze condition and performance of field devices. With ValveTriage Service the process data can be turned into meaningful diagnostic information. The service system runs 24×7, gathering data from the control system via OPC interface. It calculates several diagnostic measures bringing up the devices needing attention. Typical diagnostic measures for control valves are excessive valve travel, oscillation due to valve stiction or hysteresis and valve sizing issues. Respectively, data losses, instrument at limits, noise levels, spiking and flat-lining are followed in case of measurement instruments.
ValveTriage Service does not need any extra instrumentation on the field. It communicates with any DSC system via OPC server.
A great advantage of real-time metrics and diagnostics calculated from process data is that they can quantify the extent of the problem and its effect on the process. Rather than saying there is “some stiction” on a valve, an exact number, such as 4.2% stiction causing 2.1% variation in the process value, is supplied. This gives far more value than a “true/false” diagnostic and severe problems will receive much higher priority. The prioritization gets even more valuable when the real-time metrics are combined with devices’ criticality class information, i.e. devices impact on process, safety and environment. ValveTriage Service findings and maintenance proposal are reviewed with customer’s maintenance representatives in order to define and prioritize maintenance actions.
A typical behavior of sticky valve detected by ValveTriage service. Flowrate stays at the same level even if the control actions for valve opening is going down. When the valve finally moves, it moves too much and control system wants to open the valve. This behavior goes on 24/7 increasing process variations and causing excessive tear and wear for the valve.
The focused actions greatly reduce time spent in the field, working on wrong problems, freeing up skilled personnel to resolve the right issues and to spend time on higher-level tasks. As the number of maintenance activities go down does not only the cost of maintenance fall, but it also makes the plant safer having less events for potential faults and accidents. The ValveTriage Service delivers bottom-line results, by focusing attention to the worst behaving devices. Lifetime of equipment is extended by early detecting of excessive wear-and-tear and process performance is enhanced by bringing down process variations.
Manager, Pulp & Paper Solutions, Metso Flow Control