Valve proof take a look at credit score for a process trip

A process trip occurs when the protection instrumented system (SIS) locations the method in its protected state by commanding an automatic valve (Figure 1) or other tools to its trip state in response to an irregular course of condition. In some instances, a spurious trip happens because of a valve malfunction. In that case, the valve meeting is examined beneath real working situations, which offers a possibility to capture useful valve diagnostic knowledge.
However, such diagnostics knowledge can only be captured when automated valves are fitted with digital valve controllers (DVCs). In this text, we’ll discuss how DVCs can help determine the proof test credit for an automated valve after a course of journey.
Process journey
A course of trip happens when the SIS detects an irregular course of condition by way of sensors corresponding to temperature and stress, executes the logic and locations the process in its safe state by tripping the ultimate parts corresponding to closing an automatic valve, stopping a pump, and so forth. The SIS could communicate with the Basic Process Control System (BPCS) to close a valve downstream of the automated valve as a secondary action.
When a course of journey occurs, the main objective is often to restart the unit or equipment that has been shut down as quickly as possible. Plant engineers are busy troubleshooting and correcting problems. Maintenance technicians are busy repairing broken gadgets. Taking เกจ์วัดแรงดันแก๊ส to proof test an automated valve will not be a high priority or even an exercise under consideration because of the tight schedule after an unplanned shutdown.
Fortunately, if the automated valve is supplied with a DVC, the proof check of the valve may be thought of performed with diagnostic knowledge captured by the DVC. Also, a comparability of the diagnostic knowledge with the valve’s baseline might help discover valve deficiencies and degradations that will not show up in a proof test.
Figure 2. Proof Test vs Process Trip. Activities performed (such as repairing the device) and knowledge captured by a Fisher DVC6200 SIS digital valve controller during a course of journey meet many of the 12 requirements of a proof check.
Process journeys versus proof checks
How can proof take a look at credit be claimed for an automatic valve that has failed and caused a process trip? A proof check is a periodic take a look at performed on SIS sensors, logic solvers and final elements — similar to automated valves — to find hidden failures. These failures, if not corrected or removed, could impair the power of the SIS to take the method to its safe state when an abnormal course of situation is detected.
A proof check must be performed as per the proof take a look at interval specified within the Safety Requirement Specifications. This interval is normally decided through a mean likelihood of failure on demand calculation (PFDavg). Some customers might choose to proof take a look at based on predetermined intervals, such as proof testing sensors each 24 months and final components every forty eight months as an alternative of counting on the PFDavg calculations.
Automated valve proof tests can be accomplished offline or online. Offline proof tests are usually scheduled throughout a turnaround, when the process is totally shut down.
Proof testing an automated valve online normally requires a unit or equipment to be shut down, or the valve to be bypassed to prevent a spurious journey, making it inconvenient and expensive.
But a proof take a look at can be accomplished during a process trip.
According to IEC61511-2 Section A.16.3.1.three, “…shutdowns as a outcome of actual demand on the SIS throughout operation may be given credit as proof tests (fully or partial) under given conditions…the next planned proof check could also be skipped.”
These situations are
The shutdown paperwork equivalent data as registered during corresponding proof check.
The shutdown covers all elements of the SIS, and if not, the device or SIS subsystem not activated must be examined individually.
The shutdown occurs within a predetermined most time window before the following planned proof test which may then be canceled
When a process journey occurs, about 60% of a Safety Instrumented Function (SIF) proof test could be thought-about performed. A pattern record of activities carried out during a proof check, along with those which would possibly be performed during a process trip, is proven in Figure 2. Even with out an automated valve leak test, information captured by the DVC alone can potentially account for an excellent amount of proof take a look at coverage for an automatic valve.
The exact coverage is dependent upon the design of the automated valve, its DVC and its utility. The protection is estimated primarily based on the valve degradations, the chance of their incidence and the percentage of those degradations that can be detected by a DVC. Fortunately, information acquired by a DVC throughout a process trip can usually be sufficient to fulfill a serious part of the proof test necessities.
If the process journey takes place inside a predetermined maximum time window, the top person might choose to leverage the method trip as a proof take a look at by completing steps one through 5 in Figure 2, that are usually not accomplished in a process journey. The next scheduled proof take a look at can then be canceled. According to the Norwegian Oil Industry Association, the maximum time window should be the final half of the current proof test interval.
Figure 3. Data during a course of trip is captured by the Fisher DVC6200 SIS digital valve controller and made out there for analysis.
Common causes of valve failure
According to ISA Technical Report ninety six.05.01, the most likely root causes of automated valve degradations — which might lead to a process journey — embody:
Partial or intermittent sticking of hydraulic or pneumatic system components such as solenoids, pilots, velocity controller, and so forth., due to moisture, debris or alignment points. This causes a lack of useful margin and makes the valve slow to open or close.
Binding, galling or other degradation of valve seats or associated flow management trim that restricts or resists valve movement.
Actuator seal degradation brought on by compression, put on or looseness that reduces the stress available to actuate the valve.
Minor damage to the valve obturator plug, disk or ball attributable to system conditions, leakage or debris, together with build-up of hydrocarbon merchandise. This causes leakage.
Complete failure of hydraulic management system components similar to solenoids, pilots, pace controller, and so forth., because of moisture, particles or alignment. The valve will fail to open or close.
All of those conditions could be detected by a Fisher DVC6200SIS digital valve controller (Figure 3).
For example, a valve that’s stuck open will exhibit itself as a rise in breakout force. Loss of seat load in comparability with when the valve assembly was new signifies potential valve leak. The Fisher DVC6200SIS additionally continuously monitors for inside faults as well as its inputs such as provide stress. When the DVC6200SIS sees the provision pressure is just too low, an alert is generated (Figure 4) in order that the tip user can take corrective actions.
Figure four. The DVC6200SIS digital valve controller detected almost zero provide stress, so it alerted the management system.
Other process trip advantages
Diagnostic data captured during a process trip might reveal valve degradations that will not be detected throughout a proof take a look at. For instance, diagnostic information captured throughout a course of journey would possibly indicate an issue with the valve closing completely against the full pressure of the method, which may be an early indication of valve leakage.
The valve stroke time computed by a DVC during a course of journey is more correct underneath real operating circumstances. This results in a more correct SIF response time (the time from detection of an abnormal condition to final element reaching its trip state), which is in comparison with the Process Safety Time to make sure the SIF remains to be assembly its design necessities.
Although automated valves are very reliable, failures recognized in a course of journey can provide useful information to forestall future failures. pressure gauge ราคา can assist with turnaround planning by making sure the wanted components are available earlier than turnaround even begins to doubtlessly shorten the turnaround schedule.
A course of journey can present the protection required to delay a valve’s next scheduled proof take a look at, thus saving time and money. Data captured by a DVC could be analyzed to leverage the method journey as a proof test. Even if the top user chooses not to take proof check credit for a course of trip, the valve diagnostic data provided by the DVC may help plant personnel make proactive valve maintenance choices..

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