The decommissioning industry of offshore plants operating for oil or gas buried undersea is an emerging blue ocean. More than 10,000 offshore plants are operating worldwide up to a water depth of 2,280m, of which about 95% are in the form of a jacket platform, with the support structure jacket being the main target of the decommissioning industry.
The typical life cycle designed for these structures is around 25 years and begins with the acquisition of the right to exploration and development. An offshore plant that is required to terminate its economic activity beyond its design life cycle or be removed for other reasons must be decommissioned or reused and recycled as required by applicable laws, regulations or relevant stakeholder. Increasing aging of existing offshore plants is a major problem for oil producing countries around the world, and the importance and necessity of the decommissioning industry is rapidly increasing. In particular, the decommissioning performance of offshore plant in Southeast Asian countries is only about 5.5%, and the decommissioning of old offshore plants is emerging as an important issue.
The offshore plant decommissioning market is currently being actively formed in the North Sea and GOM(Gulf of Mexico) regions with a long history of offshore oil field development. These markets are dominated by some advanced companies in Europe and U. S. A in the form of monopoly and oligopoly. However, Korea has little experience in carrying out projects related to the decommissioning of offshore plants or subsea structures, which is high value-added industry. Underwater cutting in the dismantling operation is a preliminary process for the lifting operation of the cutting object such as a jacket, and the underwater cutting methodology and equipment like cutter occupy a very important position. In result of investigating and analyzing a number of overseas decommissioning performance projects. Underwater steel structure cutting devices are mostly classified in 3 types – Underwater Diamond Wire Cutter(UDWC), Abrasive Waterjet Cutter(AWC) and Hydraulic Sheer Cutter(HSC). Among them, UDWC is the most important underwater cutter, and is used most frequently because of the convenience and economical efficiency of operation.
This study is to develop and test a UDWC that can cut steel pipes in underwater for the first time in Korea, to make a prototype, to test and commission, and to solve various technical problems. In addition, information on the type and characteristics of the jacket, which is the object of underwater cutting work, and research on the methods and techniques related to underwater cutting were also conducted.
The drive system of the existing UDWC cutting devices generally uses a hydraulic drive, and the cost of supporting devices and equipment for supplying hydraulic pressure to the deep sea is very high.
The UDWC developed during this study uses the electric drive. And the body design and supply system using corrosion resistant material against seawater, the system to maintain constant tension on the diamond wire, the waterproofing system of the driving part and the clamping system are all designed. And the structural analysis using ANSYS, a general-purpose analysis tool, proved the safety. In addition, several tests and commissioning of various UDWC models were carried out in the water tank to develop the most optimal model. The developed UDWC was carried out to successfully cut the 300mm diameter steel pipe under water, which objectively verified the completeness of the research and development product, and confirmed that it can be commercialized with practical value and function. For the economic analysis of the UDWC developed in this study, I have compared the developed UDWC with the hydraulic systems of the advanced European companies with similar specifications. As a result, under the conditions of attaching various jigs through the follow-up advancement research in the prototype stage, the developed UDWC improved the system performance significantly and its cost was only about 50~60% in compare with the other hydraulic method.