Offshore staff

CHESTERFIELD, UK – Cathelco has teamed with UMC International to install a hull corrosion protection system on Ocean Rig’s semisubmersible drilling rig Leiv Eiriksson.

The work was performed as part of the 10 year-old rig’s class renewal program. It recently underwent a re-fit in Turkey ahead of its current campaign offshore Greenland for Cairn Energy.

The rig’s two pontoons were fitted with a Cathelco impressed current cathodic protection (ICCP) system. This comprised a 900 A, 24 V thyristor control panel wired to six anodes and two reference electrodes.

For a conventional drydock installation, holes would have been cut in the pontoons to accept cofferdams which would be welded in position. The anodes and reference electrodes would be mounted in the cofferdams and a di-electric shield applied to the surrounding hull surface. However, in this case, the work had to be performed to a tight schedule while the vessel was afloat, said Steve Ellis, Cathelco’s project development manager.

“Therefore we worked in partnership with UMC International to devise special components and diving techniques to facilitate the installation.”

The cofferdams to house the anodes and reference electrodes were attached to sections of steel of the same grade and thickness as the original hull material. Prior to installation, UMC divers created a temporary cofferdam on the outside of the hull and removed a section of plate. This new section, along with the cofferdam to house the anodes and electrodes, was then welded into position.

Divers worked on the outside of the rig to fit the anodes and reference electrodes. Finally, a di-electric shield made from PVC was placed around the anode and sealed into position.

“The project involved a considerable amount of planning to ensure that there was access for the pre-mounted cofferdams as well as designing the most efficient cable runs and co-ordinating the work to meet the deadline for completion,” Ellis added.

06/07/2011