Underwater Weld Repair of Offshore Structures

Offshore platfonvs serve as artificial bases, supporting drilling and production facilities above the elevation of waves. They have to sen/e in harsh environments and hence are likely to be damaged. Therefore the damaged structure has to be repaired to enable it to continue to sen/e its intended function during its designed life. There are over 7000 offshore platforms worldwide. It has been estimated that, globally more than 50 platforms per year require some form of upgrading, strengthening and/or repair. The strenghtening and repair of existing offshore installations is an important part of offshore engineering. Design codes provide little or no guidance in this area. The need to repair or strengthen offshore installations is likely to increase due to various causes.

Many offshore structures, damaged during their operation, have been repaired using welding technique. The currently available welding technique used in underwater jacket repairs can be broadly classified as Hyperbaric or Habitat welding. Cofferdam welding and Wet welding.

Different welding processes that are employed in dry Hyperbaric welding are : SMAW, GMAW, FCAW, etc. Special electrodes have been developed for carrying out wet welding processes. Automated wet unden/\/ater welding for construction of offshore structures, called Mega-float, has been developed. A mechanized wet welding by the water curtain nozzle was executed for the Mega-float during open field demonstration in July 1996 at Yokosuka harbour.

The paper has dealt with the current underwater welding processes which have been adopted for the repair of damaged offshore jacket platforms. Case histories of welded repair of existing platforms are also reviewed Problems associated with the under water welding processes and difficulties faced in their applications are also discussed.