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Battery-operated non-intrusive inspection for rapid acoustic emissions monitoring solution in hazardous areas

Project Summary

Acoustic emissions monitoring of crack growth is an established technique, supported by significant research and studies. The technique involves recording signals from active non active defects during the monitoring period – thus indicating whether the defect is dormant or requires intervention.

This specific NZTC-supported project examined the suitability of a hazardous-area-certified, battery operated acoustic emissions monitoring system (AEMS) for non-intrusive inspection. The AEMS was deployed to detect the presence of active chloride-induced stress corrosion cracking in an austenitic steel pressure vessel.

This project monitored a patch repair on the east dome of a LP Flare KO Drum. The stainless steel (316) pressure vessel underwent an inspection in 2013 and a through wall crack was identified on the east dome at the six o’clock position. This defect provided an ideal trial location to determine if acoustic emission monitoring was a suitable technology to monitor the defect as part of a non-intrusive inspection (NII) regime.

The main objective for this project was to address the feasibility of deploying a battery powered AEMS in a hazardous area.


Industry value:
The AEMS is designed for rapid deployment – with no requirement for extensive signal cable installations or external power, therefore minimising the resources required to initiate vessel monitoring in offshore environments.

Key results:
Following data processing, acoustic emissions activity was clearly located within the sensor array on the dome head. 73% of this activity was identified as having occurred at one specific period with correlation to the maximum temperature reached on the vessel.

During the initial monitoring period, seven days’ worth of data was acquired, while in the second monitoring period 4.5 days of data was acquired. During these periods, there was a constant level of activity below 60dBAE, with a few periods of activity reaching 90dBAE.

A review of the location results from the acquired data showed clear indication in the form of a concentration of activity on the dome of the vessel which was within the area of the damage identified in previous inspections.

The system was installed on site and commissioned with its operation successfully demonstrated.

Lessons learned:
Despite the bench testing conducted at Mistras prior to deployment, the performance of the acquisition system was reduced due to a time lag of the two months between the system being shipped and its installation.

The self-discharge of the batteries significantly reduced the available charge to operate the AEMS when it was installed. Li-ion batteries would be preferred to reduce such effects, however they were not originally chosen due to their associated hazards with them. Depending on monitoring period requirements for future deployments consideration will be given if one or two batteries are to be used, which will be shipped in advance of installation to allow maximum charging.


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