Mechanized Underwater Welding and Cutting Techniques for VLFS

A0110 Yoji Ogawa Organization National Institute of Advanced Industrial Science and Technology (AIST)

Mechanized underwater welding and cutting techniques are very

important for actual usage of very large floating structrures (VLFS).

In the case of construction, offshore welding plays a major part of

construction process. The total weld line is very long and a half

part is submerged under water. Water curtain type wet underwater

welding technique had shown its excellent ability for the construction

of a Mega-float which was carried out by the Technology Research

Association of Mega-float. A mechanized underwater welding machine in

over head position was also developed for maintenace of the Mega-float.

A kind of public facilities like offshore airport requires frequent

maintenance and alterlation to catch up the latest needs. Therefore

underwater mechanized cutting technique for alterlation and

dismantling has developed. At the final stage of the Mega-Float

project, we had dismantled the whole structure into eleven small units

to reconstruct another usage. In case of alteration, quality and

operating cost of cutting are very important. Therefore, we used

mechanized underwater flame cutting. Total length of underwater flame

cutting was more than 1000 meters. High quality cut was obtained

under sever condition such as heavy attachment of bio-fouling on the

bottom. This paper describes general aspect of mechanized underwater

welding and cutting techniques for an actual VLFS.