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The Eddy Current technique is known to be very sensitive in the detection of surface breaking cracks in ferromagnetic material.

An expert in Eddy Current techniques for non-destructive testing, Innospection completed a surface breaking crack detection job on a platform sub-structure in the Norwegian waters amidst rough working environment and a tight inspection schedule.

As part of a planned lifetime extension of the platform sub-structure, Innospection performed an inspection on the specific cast nodes and welded connections, particularly at the critical areas with the highest stress level on the jacket structural legs. The target of the inspection was to verify potential fatigue-induced surface cracking and to demonstrate the integrity of the sub-structure.

The Eddy Current crack detection technique can be applied on bare metals, welds and heat affected zones. Performed using mainly single sensors, the crack detection can also be carried out using multiple sensor arrays or manipulator guided sensors depending on the geometry of areas to be inspected and the detectability criteria.

Utilised for the inspection was a marinised Eddy Current multiple sensor array customised for large area coverage with deployment by divers. The equipment was deployed to the inspection areas using a light dive craft deployed from a vessel.

As the Eddy Current induced field is most sensitive in detecting cracks where the field line orientation is perpendicular to the orientation of the cracks, the multiple sensor array was driven in at least two orientations at 90 degree apart. The depth of the detected cracks was to be verified using Pulsed Echo Ultrasonic testing.

Despite the rough sea and working environment within the light dive craft, the inspection was performed to the highest productivity on 24 hours shifts with the seamless changing out of inspection operators and divers, leading ultimately to a shorter vessel time.

The inspection results showed excellent signal to noise ratio which confirmed the high detection capabilities of the Eddy Current multiple sensor array. Although some findings were indicated, there was no fatigue-induced crack at the inspected areas. The inspection campaign was completed successfully within the required time frame to the client’s full satisfaction.