Caisson Internal

Detailed Internal/External Inspection of Caissons on North Sea fixed platform.

Various inspection surveys were performed on the platforms caissons over a 4 year, operations including GVI, UT Thickness, CP, Cavi Cleaning & 3D laser profiling.

An initial external inspection identified anomolies at a circumferential weld during a periodic subsea structural inspection

Internal surface profiling of circumferential weld in Firewater Caisson.

The objective of this 2014 survey was to profile the internal surface of a circumferential weld that had been subject to corrosion.  This was done to assess whether any wall loss or through wall penetration had occurred at the circumferential weld as a result of the corrosion.

HPR utilised OceanTools C-Scan, which is made up of the C-Gauge laser system mounted onto an encoded subsea electric motor and can be used to scan the full 360˚ of a circumferential weld.

Based on welding coating records and the results of a previous HPR internal inspection of FC2 in 2012, it was known that excess internal corrosion would be found at the circumferential weld and would have to be removed using the CaviBlaster cleaning system in order to accommodate effective laser measurements.

The C-Scan was deployed to depth on a specifically designed laser rig with the aid of the ROV rather than mounted to the ROV.  However recent progress had been made with the deployment of the C-Scan mounted on the Outland 2000 ROV.

 

 

The image above shows the full 360 degrees profile of the circumferential weld once the cylindrical shape of the caisson is unwrapped.  Four anomalies are also highlighted with reference to platform North.