Partial stroke testing is moving the valve partially from the normal position towards the fail-safe position, according to predefined parameters. The pneumatics test is used to check that the internal pneumatic system of the ValvGuard is working as expected. This test does not affect the process in any way since it only moves the spool valve in a controlled way so that the actuator does not react.
Load factor and breakaway pressure trends
Two basic statistical diagnostic features are available in Neles ValvGuard: load factor and breakaway pressure trends. Both trends are based on the data available from partial stroke testing.
Load factor (LF) is used to express how much of the available force in the actuator is used to move the valve. Normally this is somewhere between 20-40 %, but it depends heavily on actuator size, valve type and size, and also the process conditions. LF is calculated after every PST and the trend is updated accordingly. The alarm limits for the LF can be set, and when the LF exceeds the predefined limit the alarm is triggered. Even before the alarm is triggered, it is easy to see from the trend if the condition of the emergency shutdown valve package is degrading. If e.g., the load factor is increasing, it can mean that the friction in the valve has increased for some reason. Necessary actions can be planned to check or replace the valve during the next shutdown, or it can be decided that the valve degradation is too fast, and the valve needs to be serviced before that.
Breakaway pressure (BP) measurement calculates the point where the spring force overcomes the pressure in the actuator and starts to move the valve. Also, BP is calculated after every PST and the breakaway pressure trend is updated accordingly.
All of these trends are kept in the device memory and can be uploaded at any time. This history trending is a unique feature, which most of our competition lacks. There are also so-called device alerts available, which can warn of decreasing supply pressure, valve position deviation from the normal state or increasing device temperature etc.
One of the important diagnostics related features in ValvGuard is the Safety View, which is available online in our DTM, Neles Valve ManagerTM. This main DTM view summarizes the condition of the safety valve assembly at one glance. Diagnostics of the valve assembly is categorized into four different parts and it is easy to find if there are any issues with the valve.
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