Understanding Subsea Acoustic Leak Detection and Condition Monitoring – Part 2

In any given subsea field there is a multitude of equipment, that need to be constantly monitored. Subsea Multi-Domain Condition Monitoring can be achieved by introducing additional hydrophones, specially designed for detecting sound from rotating machinery, subsea processing equipment, structural integrity, fluid flow rate variations among others. The latest high-end sensor systems ally acoustic condition monitoring with acoustic leak detection. This works in much the same way as surface-based acoustic emission monitoring and can be used to monitor rotating machinery to check speed tracking and resonant frequencies. It can also monitor rotational equipment in subsea plant such as bearing damage, unbalanced pumps, mechanical breakdown and reduced efficiency. It can identify structural vibration and detect irregularities and defects in valves and chokes. Multi-domain condition monitoring can be further extended by employing sensors that measure underwater electric potential or stray alternating electric field, emanating from sub-sea electronics equipment, machinery and cables. When used in combination with acoustic condition monitoring, these can be used to determine the electrical condition of subsea machinery and plant in detecting electrical faults, establishing electrical signatures for subsea machinery, monitoring electrical power and obtaining very precise measurements of conditions such as pump slip ratios.

Data processing of acoustic signals and other sensor data can be performed subsea by encasing the electronics in titanium underwater housings. Alternatively, data processing can be transmitted topside to be carried out on a dedicated workstation. Data processing speeds can be increased and data display enhanced by employing powerful hardware and efficient software. Subsea equipment found in subsea fields produce wide a range of different noise levels and structural obstructions within the equipment can cause reflections and attenuations of the noise. When setting up a subsea leak detection system combined with a condition monitoring system, extra care needs to be taken when first installing the sensors in order to guarantee a precise configuration of sensor parameters. These will vary according to the characteristics of specific subsea installations in an oil field, yet advanced monitoring software feature pre-set operating parameters and noise signals of a variety of equipment used subsea, including noise signatures expected when certain equipment problems occurs, such as the noise made by misaligned rotating pump axel. Pre-set trend values of the noise enable identification of the location of the problem within the pump. All expected ambient and equipment generated noise variation values are normally pre-set in the monitoring software, providing powerful, yet very user-friendly graphical user interfaces.