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“Into the Deep” with ACFM for Subsea Swivel Joint Inspection

In response to a recent subsea swivel joint inspection campaign

August 12, 2016 – TSC rose to the challenge to design and build a bespoke scanner to enable ACFM inspections at 1100m.

Swivel joints are an integral part of subsea pipelines and water injection systems, installed as part of the extraction infrastructure in subsea oil fields. Swivel and pipeline welds are made of a corrosion resistant alloy to avoid excessive corrosion. However, within the scope of TSC’s project, some of these joints had been identified as “leaking”, causing a reduction in productivity of the well. Information and data on the exact nature of the failures were needed in order to schedule a repair and maintenance programme.
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TSC’s ACFM® inspection technology has been developed to detect and size fatigue cracks in metal structures, with great accuracy, producing instant repeatable and auditable measurement data. The ACFM® NDT method is tolerant of lift-off and misalignment; and as such is suitable for the deployment by ROV techniques in an underwater environment. For this reason ACFM® was chosen and used to inspect the identified swivel joints to determine if there were fatigue defects present, as the detected leakage could be a result of cracking. ACFM® was able to accurately size the known defects but was also deployed to determine if there was further cracking in the other swivels that could lead to failure in the short term. Automated UT testing provided by Sonomatic was also used to check the inside surface of the pipe for corrosion.

TSC’s ACFM® equipment is rated for deepwater work up to 2000m depth. A scanner solution was custom designed and built in-house by the TSC engineering team, to work around the specified swivel joint geometry at the required depths. The scanning system also operated to cover the full circumferential weld of the pipe/swivel joints. The scanner maintains contact on the pipe by magnets and moves around the pipe guided by wheels travelling on the the pipe surface. The ACFM® probe is sprung to maintain contact with the weld being inspected and to minimise lift-off for optimum sensitivity. As the ACFM® inspection technique works through coatings, the epoxy surface preparation did not hinder the inspection.

Overall this deep sea inspection campaign was completed successfully and it was confirmed that no further fatigue cracks present. However there were corroded areas identified on the inner surface of the pipeline. Clamps were fitted to seal the leaking sections and to improve productivity of the well. Further IRM activities are now being scheduled.

The accompanying picture shows the ACFM scanner working on the pipeline at 1100m depth.

Source: NDT.org

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