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Seaward Goes Above Ground for Dive Operations

Posted March 27, 2014
Written by Cecil C. Achord
Seaward Marine Services was tasked to perform a general inspection, a Visual Inspection, a Video Inspection and an Ultrasonic Thickness Measurement Survey, using DataScanSM, of an Aboveground Storage Tank (AST) at one of the country’s largest nuclear power facilities.  The weeklong project with mobilization from Seaward Marine’s Norfolk Virginia office included entry into the 300,000 gallon AST by divers dressed in total enclosure suits to ensure no contamination of the tanks cargo.  Because of tank depth, in excess of the no decompression limits, under Seaward Safe Diver Standards divers had to change out at regular intervals ensuring diver safety.

The first order of business was to vacuum sediments from the bottom of the liquid filled tank to ensure a thorough visual and video inspection of the tanks interior surfaces. Visual inspection revealed a faulty tank level indicator system which was promptly repaired and calibration procedures performed.

Next, divers installed a reference grid system within the tank in which to perform a very accurate ultrasonic thickness survey using DataScanSM. The ultrasonic thickness survey,  performed on a one foot by one foot grid pattern producing a nearly 100% probability of detection, collected over 530,000 individual thickness readings, several of which were below the thinning criteria established prior to the inspection.  The thickness data will be used to formulate repair or replacement estimates and on subsequent surveys to determine tank life cycle estimates.

The inspection and survey performed by American Society of Non-Destructive Testing (ASNT) certified personnel and procedures came in under schedule and under budget allowing the tank and facility to continue with uninterrupted operational scheduling. A second tank, at the same facility is scheduled for survey during the plants next outage.

Seaward Marine’s DataScanSM Ultrasonic Measurement System provides a thorough analysis of the condition of metal in the region of the measurement, as opposed to single-point readings of metal thickness. Seaward’s development of an automated system that compensates for roughness so that all areas of the reading location can be quickly and accurately measured.


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