Case Study: Offshore Oil Platforms Use PC-Based Condition Monitoring & Control

Summary

Around the globe, ensuring a reliable energy supply is essential for every industrialized nation. For example, 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 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.
 
The steel structures of an offshore platform are exposed to extreme environmental conditions throughout their 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. 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.

 
Analog I/O enables data acquisition

For the pilot project, a production platform off the Chinese mainland in Bohai Bay allowed continuous monitoring of a typical offshore rig. Various measuring points were specified based on the platform’s construction plans and onsite investigations with integrated electronics piezo-electric (IEPE) sensors recording vibrations. Their signals are acquired by oversampling capable terminals for condition monitoring (IEPE) and transmitted to an 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 (Figure 1). 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.

Real-time vibration analyses

The vibration monitoring system comprises 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 IEPE terminals. The control functionality and synchronous scanning with up to 50 ksamples/s and 16-bit resolution ensure vibrations are captured in real time.
 
After analysis, processing, and storage of the sensor data by the 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.