- By Jesse Hill
- June 02, 2023
- Beckhoff Automation
System-integrated vibration analysis reliably monitors the load-bearing capacity of steel structures in offshore energy production.
Around the globe, ensuring a reliable energy supply is essential for every industrialized nation. Case in point: China's largest producer of oil and gas, the China National Offshore Oil Corporation (CNOOC), places great value on monitoring the condition of its offshore platforms to ensure their structural integrity. In a corresponding initiative, Tianjin Aoling Industrial Automation Technologies Co., Ltd. (Aoling) leveraged vibration analysis to monitor and reliably predict the offshore structures’ load-bearing capacities. To connect these technologies, the Aoling engineers rely on PC-based control and highly precise, system-integrated measurement technology from Beckhoff.
The steel structures of an offshore platform are exposed to extreme environmental conditions throughout their entire service lives. Difficult sea conditions ranging up to freak waves and aggressive seawater prey upon them without interruption. Microorganisms in the water cause severe electrochemical corrosion, which also weakens the mechanical integrity of the structures. Furthermore, remote offshore platforms are notoriously difficult to access for regular maintenance, much less in emergency situations.
Structural Defects that would cause a standstill of the entire system or even an oil platform accident would be correspondingly costly. As such, CNOOC places high importance on recording the real operating conditions and environmental influences at work on the platform structures.
EtherCAT analog I/O terminals enable data acquisition
For the pilot project, a production platform off the Chinese mainland in Bohai Bay allowed for continuous monitoring of a typical offshore rig. Various measuring points were specified based on the platform’s construction plans and onsite investigations with IEPE sensors recording vibrations. Their signals are acquired by oversampling-capable EL3632 XFC EtherCAT Terminals for condition monitoring (IEPE) and transmitted to a CX2020 Embedded PC with up to 50 ksamples/s for evaluation.
The measurement system monitors the operating conditions of the platform and uses the vibration data to analyze the loads on the steel structure. The objective of the pilot project was to ensure the integrity of the structures during their entire operating period and to accurately predict the service life based on early indicators. This enables the implementation of preventive measures as required.
Responsible for the implementation of the demanding project is Aoling. The company has focused for years on the protection of offshore applications against wave energy, performing research in this area in collaboration with many Chinese universities, colleges and research institutes. Aoling develops innovative solutions, such as condition monitoring implemented with Beckhoff technology.
"Condition monitoring and diagnostics are akin to intensive medical monitoring for the platforms. In comparison to competitors' systems, Beckhoff offers ideal diagnostic tools for this purpose," explains Fan Lipeng of Aoling.
Real-time vibration analyses on offshore structures
The vibration monitoring system comprises a total of 48 acceleration sensors, which have been mounted in explosion-proof housings in accordance with the operating conditions. From the measurement points, the signal lines of the vibration sensors proceed to the control cabinet in the central control room, where they are connected through a routing level to the two-channel EL3632 IEPE terminals. The XFC functionality and synchronous scanning with up to 50 ksamples/s and 16-bit resolution ensure that vibrations are captured in real time.
After analysis, processing and storage of the sensor data by the CX2020 Embedded PC, the information is transferred to a main computer on the oil platform for secondary calculation and storage. Visualization, alarm functions and data archiving are implemented there. At the same time, the master computer transmits all data to a central control room on shore via a fiber optic line.
At the same time, TwinCAT and the analytics application developed by Aoling in a high-level programming language are running on the CX2020, which simplifies data management and storage, according to Fan Lipeng. In addition, the wide array of available I/O modules, their compact design and the flexibility of EtherCAT in terms of topology support later expansions and integration of additional functions. Aoling plans to increasingly use the advanced control technology from Beckhoff for condition monitoring. The intention is, for example, to gradually implement machine learning, artificial intelligence (deep learning), neural networks and other functions on the standard TwinCAT platform. In this way, the offshore rigs can maintain safe, reliable production.
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