Shutdown Valve Partial-Stroke Control for Accurate Stuck Detection
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Solution Overview
Problem
Current methods for conducting partial-stroke tests on emergency shutdown valves are inefficient and inaccurate, as they often result in significant travel deviation and error signals, leading to misleading results and prolonged test times due to differences in design considerations compared to control valves.
Innovation Solution
A valve controller generates a setpoint signal that ramps from an initial value to a target value, then back, without requiring the valve to reach a hard cutoff, and applies acceptance criteria based on actuator pressure and travel to accurately determine stuck valve conditions, allowing for quick and reliable partial-stroke testing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If positioning technology developed for control valves is applied to shutdown valves during partial stroke testing, then the valve can be tested, but significant travel deviation and error signals occur leading to inaccurate results
Solution Approach 1:
The patent modifies the setpoint signal parameters specifically for shutdown valves during partial-stroke testing. Instead of using standard control valve positioning parameters, the system adjusts the setpoint signal to account for shutdown valve characteristics such as high friction seals, loose linkage, and large volume, thereby eliminating travel deviation and error signals while maintaining test accuracy
Solution Approach 2:
The patent inverts the conventional approach by not requiring the valve to catch up to the setpoint signal. Instead, the setpoint signal is designed to accommodate the valve's movement characteristics, allowing the valve to move without needing to precisely reach the setpoint, thus eliminating the source of error signals while maintaining effective testing
2Reliability
If the valve is required to reach a hard cutoff during partial stroke testing, then complete valve travel is tested, but the test time is prolonged and pressure readings indicate stuck valve conditions incorrectly
Solution Approach 1:
The patent applies partial action by not requiring the valve to reach the hard cutoff position during partial-stroke testing. The setpoint signal is designed to stop before the hard cutoff, allowing the test to complete successfully without the problematic pressure readings that occur at hard cutoff, thereby reducing test time and eliminating false stuck valve indications
Solution Approach 2:
The patent converts the potential harm of hard cutoff pressure readings (which indicate stuck valve conditions) into a benefit by designing the setpoint signal to avoid hard cutoff entirely. This approach uses the knowledge of hard cutoff problems to create a test methodology that bypasses the issue, transforming a harmful condition into a design constraint that improves test accuracy and speed
3Ease of operation
If venting the actuator from a hard stop is performed, then the valve can be repositioned, but considerable time is required and significant travel deviation occurs
Solution Approach 1:
The patent applies preliminary action by preparing the setpoint signal in advance to account for the valve's position at the hard stop. The system anticipates the valve being at hard stop and designs the setpoint signal accordingly, eliminating the need for time-consuming venting operations and significant travel deviation by pre-calculating the appropriate signal parameters
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.