Shutdown Valve Partial-Stroke Testing for Stuck Valve Detection
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Solution Overview
Problem
Current methods for conducting partial-stroke tests on emergency shutdown valves are inefficient and inaccurate, often requiring prolonged test times and producing misleading results due to high friction, large actuators, and design differences from control valves.
Innovation Solution
A valve controller generates a setpoint signal that ramps from an initial value to a target and back, with acceptance criteria for actuator pressure and travel to determine if the valve moves from a hard stop and detects stuck conditions, allowing for quick and accurate partial-stroke testing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional control valve positioning technology is applied to shutdown valves during partial-stroke testing, then the valve can be tested for positioning accuracy, but the test takes considerable time and introduces significant travel deviation due to high friction and large actuator volume
Solution Approach 1:
The patent changes the control parameters specifically for shutdown valves during partial-stroke testing. Instead of using conventional positioning technology parameters, it implements a specialized control algorithm that accounts for the high friction and large actuator volume characteristics of shutdown valves. The system adjusts the setpoint signal generation and acceptance criteria to match the specific dynamic characteristics of shutdown valves, enabling accurate and rapid testing without the time delays and travel deviations associated with conventional approaches.
2Reliability
If larger actuators are used on shutdown valves to achieve full closure, then the valve can reliably shut off flow, but the actuator produces larger error signals that require slower testing
Solution Approach 1:
The patent implements dynamic acceptance criteria that adapt to the actuator size and error signal characteristics. The system uses dynamic thresholds for position error that are scaled according to the actuator volume and expected error magnitude. This allows large actuators to be tested at higher speeds without compromising reliability, as the acceptance criteria automatically accommodate the larger error signals while still detecting actual malfunction conditions.
3Manufacturing precision
If hard cut-offs are applied at the end of a partial-stroke test to ensure complete valve closure, then the valve reaches full position, but the pressure readings indicate stuck valve conditions even when the valve operates properly
Solution Approach 1:
The patent introduces an intermediary evaluation layer between the hard cutoff action and the stuck valve determination. Instead of directly interpreting pressure readings from hard cutoff as stuck valve indicators, the system uses a specialized evaluation algorithm that distinguishes between normal hard cutoff pressure transients and actual stuck conditions. The acceptance criteria incorporate knowledge of expected pressure behavior during legitimate hard cutoff, filtering out false positives while maintaining detection of genuine stuck valve conditions.
4Productivity
If conventional acceptance criteria are used for partial-stroke testing, then the test can be completed, but the results are of little value for supervision and maintenance of shutdown valves due to design differences
Solution Approach 1:
The patent implements feedback-based acceptance criteria specifically tailored to shutdown valve characteristics. The system continuously monitors valve position, actuator pressure, and travel characteristics during the test, comparing these measurements against shutdown valve-specific thresholds and patterns. The acceptance criteria provide feedback that distinguishes between normal shutdown valve behavior (high friction, shallow bench set effects) and actual malfunction conditions, ensuring that test results contain actionable diagnostic information for maintenance personnel.
Data Source
AI summary
To generate a setpoint signal to stroke a valve during a partial-stroke test, a first target is determined for the setpoint signal based at least on a travel displacement threshold, the travel displacement threshold corresponding to a desired extent of travel of the valve during the partial-stroke test; the setpoint signal is ramped from an initial value to the first target, during a first time interval; subsequently to the first time interval, the setpoint signal is maintained at the first target during a second time interval; a second target is determined for the setpoint signal based at least on the initial value; and during a third time interval subsequent to the second interval, the setpoint signal is ramped from the first target to the second target in a direction opposite to the ramping of the setpoint signal during the first time interval.