Leak Detection (ALD)
The Naxys ALD detects and localizes any leak (hydraulic, oil, MEG, water or gas) at distances up to 500 meters (depending on differential pressure, leakage rate and background noise). Providing excellent area coverage, only one ALD is required to monitor a large manifold or a cluster of wells. Since 1st version installed in 2006, more than 100 systems have been permanently deployed on the Norwegian Cont. Shelf, Gulf of Mexico and Africa. Although based on the same technology since 2006 the electronics and software has been continuously updated to minimize the risk for false positive and false negative alarms.
On behalf of The Norwegian Oil and Gas Association, SINTEF Petroleum Research performed an assessment of available technologies for subsea leak detection.
For the ALD the conclusion was as follows:
The system detects both gas and crude oil leakages very well, and is well suited for area coverage.
Gas leakages are in general easier to detect than crude oil leakages.
The most important parameter for detection is the pressure difference across the leakage opening, due to the creation of acoustic noise.
If the pressure difference is above around 5 bar, leakages are easily detectable within a range of at least 10 m.
The detection is also dependent upon the distance to the leakage and the size of the leakage opening.
Localization of the leakage is possible.
Other leaking fluids should also be easily detected, as long as there is a pressure difference across the leakage opening that generates sufficient acoustic noise.
The ALD is also used for Flow Induced Vibration monitoring, choke and valve monitoring and can be used proactively by providing early warnings (e.g. vibration) and allow the operators to take actions before an incident escalates into a leak, ref DnVGL RP-F302, appendix B Leak Detection Techniques and their characteristics.
Norwegian regulations require that integrity of the leak detector shall be maintained during the entire life of the installation, to ensure that it carries out its required functions (Act regulation §45). The maintenance shall include monitoring of performance and technical condition, to identify and correct potential failure modes that are under development or have occurred (Act regulation, §47).
Naxys has a dedicated service team providing:
Remote access to subsea sensors.
Technical check and verification of systems.
Review of data and events from latest period.
Evaluation of warning/alarm threshold.
Simulation of subsea leakages by ROV operated tool.
Leak Detection (LLD)
The Naxys Local Leak Detector (LLD) is an ultrasensitive instrument within the category DNVGL* is referring to as “point sensing sensors”. The LLD provide real time leak rate and will detect even single gas bubbles passing the sensor head. In line with DNVGL recommended practice the LLD is designed to be installed over critical points considered to have the highest leak probability and with a potentially higher leak rate – this will typically be subsea components with high pressure flow and more complex geometry like valves, flanges, joints etc.
Please note that a limitation to “point sensing sensors” is that direct contact with the leaking medium is required. Seawater currents or buoyancy effects may lead the leaking medium away from the sensor. We solved this by installing a collector for hydrocarbons above the area considered critical and the LLD is installed at the top of the collector, see illustration below. To be in line with the recommended practice by DNVGL, we recommend that a point sensing sensor is combined with a sensor able to perform detection over an area (not limited to point sensing), e.g. the Naxys ALD sensor.
*Recommended Practice, DNV-RP-F302, SELECTION AND USE OF SUBSEA LEAK DETECTION SYSTEMS, April 2010
Naxys Acoustic Electric Monitoring system (Naxys AECM) uses acoustic and electric monitoring techniques to non-intrusively monitor the subsea rotating equipment. The system provides the operator with Key Performance Indicators (KPI). This gives the operator the capability to head off issues earlier, diagnose and tune pump|compressor performance for greater efficiency.
Key Performance Indicators, e.g. imbalance detector, event detector, sub-sync. detector, harmonics (acoustic signature), slip ratio (load), measured speed (RPM), measured VSD freq., electric signature, band energy.
Audio: Real-time and playback of start-up, shut-in, trip, events, etc.
Pump|compressor monitoring can be combined with subsea leak detection.
Early detection of change in pump|compressor behavior and automatic warning to Operator.
Non-intrusive system. Do not interfere with pump |compressor.
Qualified and field-proven.
Forms part of the Operator’s condition-based operation and predictive maintenance strategy.
The Naxys Acoustic Vibration Monitoring system detects and trend vibrations on subsea structures. The sensor provides full area coverage meaning that a single sensor can cover a large structure, e.g., a manifold. If a vibration is detected on any part of the structure, the sensor will give information about direction and start trending vibration level. Machine learning is applied to identify normal vibration levels and an alarm will only be triggered if these are exceeded. Typical applications are monitoring VIV (Vortex Induced Vibrations) FLIP (Flow Induced Pulsation) and FIV (Flow Induced Vibrations). The system is used for continuous monitoring and trending of vibrations providing the Operator with an early warning if the subsea asset is operating outside the defined limits. The system can be combined with the Naxys leak detection system, ALD.
Wide area vibration monitoring
Flow velocity tuning to avoid vibrations
Detection of damaged pipe support
Detection of loose components
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Both the Naxys ALD and AECM sensors are designed to monitor the operation and condition of valves and are also used to maximize choke lifetime by avoiding cavitation. Monitoring includes detection of fault conditions like leaking valves and broken return spring on fail-safe-close valves.