Diagnose Valve Problems Remotely
ValveWatch® is a condition monitoring system for critical valves that delivers proven results. ValveWatch utilizes advanced technology to remotely monitor valves and actuators, detecting problems before they impact production.
How It Works
The ValveWatch system incorporates sensors attached on or near the valve and actuator assembly to routinely monitor and record their performance. Strain sensors and actuator pressure sensors monitor valve & actuator performance during operation, while dynamic pressure sensors and acoustic sensors monitor the valve for internal seat leaks. Together, these sensors provide operators an automated checkup on the condition of the valve and actuator package.
The strain sensor and actuator pressure sensor provide valuable diagnostic data each time the valve strokes. The strain sensor is permanently bonded to the valve yoke adapter and records the force applied to the valve by the actuator during a valve stroke. Problems with valve operation, including damage to certain components, are readily detected using data taken from this sensor.
An actuator pressure sensor mounted to the actuator supply line records the change in actuator pressure throughout the valve stroke. Damage to the actuator or a problem with the actuator air or hydraulic supply can be detected using this sensor. The actuator pressure sensor is also used to determine when the valve changes position, causing ValveWatch to initiate a valve stroke test.
For ball valve and slab gate valve designs with sealed cavities, dynamic pressure sensors are used to test the valves for leaking valve seats. Unlike other methods of leak detection that require valves to be closed for testing, ValveWatch allows operators to monitor and identify leakage while valves are open and production is flowing. This innovative technology gives operators the ability to trend valve seal performance and proactively plan for maintenance or repair.
Two dynamic pressure sensors are used: one installed in the valve cavity and one installed upstream or downstream of the valve. During a typical leak test 60,000 readings are taken from each of these sensors. They record the fluid oscillation in the sealed valve cavity, and compare the frequency and amplitude to the oscillations to those measured in the upstream or downstream flow. As the signals become similar in shape and amplitude operators are immediately warned of a potential seat leak.
For valves without a sealed cavity an ultrasonic sensor is installed downstream of the valve. The valve must be stroked closed, and a slight differential pressure is applied across the valve seat to detect a leak. If the valve seats are leaking, high-frequency noise generated by the gas or liquid media passing through the seat will be detected by this sensor.
Data is collected from the sensors by the Local Data Acquisition Unit (LDAU) Assembly which consists of an IP66 weather proof box containing several modules installed as close as possible to the valve. The standard system includes two Strain/AC modules and a Communications Module. The strain channel monitors signals from the strain and static pressure sensors, and the AC channels handle the dynamic pressure sensors. The signals are conditioned and converted to digital in the sensor modules and passed to the Communications Module for wireless or data-over-power transmission to a HUB Assembly. The LDAU Assembly and the sensors are intrinsically safe and are certified according to North American and European standards for installation in Zone 0 areas.
An additional communications and Ethernet module are housed in the HUB Assembly along with all the power supply, terminal strips, and intrinsically safe barriers. The HUB assembly is rack mounted in a safe area (Zone 2) or equipment room. Each Hub assembly can be configured to monitor up to eight valves. An Ethernet cable connects the HUB to a server where the data is stored, transmitted, and then analyzed for leakage. All the test results and data are stored in a secure Oracle database application.
ValveWatch collects data from the dynamic pressure sensors on a scheduled interval or when the valve strokes, while data from the other sensors is recorded only when the valve strokes. For leak tests using dynamic pressure sensors, the system software performs the leakage calculations using patented algorithms that run automatically. The test results are compared to pre-established limits, and alarms warn operators of degrading seal conditions. For valve stroke tests, data taken from each sensor is compiled into a signature and compared against a baseline signature taken under “normal” conditions. Irregularities in valve signatures are identified and analyzed to determine the source of the valve or actuator problem.
A simple web interface allows easy access to the system status from any location. Security is provided so that only authorized persons can access the system map, alarm window and system tree to view platform, valve and sensor status. The software provides reports and trending plots so that operators can evaluate ongoing performance.
ValveWatch Monitors Performance 24/7
Partially blocked exhaust ports can significantly increase valve closing time. With ValveWatch, measurements taken from the actuator pressure sensor during a valve stroke can identify this problem. This example shows a signature from a valve with a blocked exhaust port compared to several signatures from a normal valve. The blocked exhaust caused an increase in stroke time of 500% for this valve. Left undetected, this problem can compromise the performance of critical systems such as ESD systems.
Bent valve stems can significantly accelerate packing wear. With ValveWatch, data taken from the strain gauge during a valve stroke can identify when this problem is occurring. This example shows a signature taken from a gate valve with a bent stem. As the valve strokes open, the bend in the stem causes a rapid increase in the thrust required to partially open the valve, followed by a rapid decrease to normal thrust required to complete the stroke. This hump in the thrust signature is an indication of a bent valve stem, and left undetected may result in external valve leaks.
Excessive breakout torque can eventually result in valves seizing. This example shows strain gauge signatures taken over four strokes of an offshore shutdown valve. The first three signatures display the significant increase in torque required to open the valve. The excessive torque is also apparent in the running load throughout the full stroke. The final signature was taken after the operator serviced the valve to bring it within normal specification. Left undetected, this valve could have seized without warning and compromised the safety of the facility and its workers.
Air leaking from the actuator may prevent the actuator from overcoming its spring pressure. The result is a valve that does not open completely. This example shows signatures taken from two valves using the actuator pressure sensor. The top signature depicts a normally opening valve, while the lower signature depicts a valve that fails to stroke fully open when the actuator is charged. Without monitoring, actuators may leak air for extended periods before this problem is identified.
Excessive friction can be the result of several damaging issues inside the valve, including internal corrosion, deposit formation, or over-tightened packing. This example shows strain gauge signatures taken from two valves during a full open stroke. The bottom signature shows a normally operating valve with a smooth strain signal throughout the valve stroke. The top signature shows a jerking motion as the valve moves fully open. Often invisible from outside the valve, the rapid peaks and valleys in the strain signal are the first signs of excessive friction and a potentially damaging valve problem.
Without ValveWatch, leaking valve seats cannot be detected without closing the valve and conducting a manual leak test. In this example, a seat leak was identified in an offshore shutdown valve by ValveWatch while the valve was fully open and production was occurring. Readings from the dynamic pressure sensors exceeded limits and alerted personnel to the problem. Operators confirmed a small leak of 100ml within 30 minutes and repaired the valve before the leak developed further. Without ValveWatch, this seat leak would have gone undetected and may have developed further until identified during the next manual test period.
