Offshore Repair Work
Difficulties may be encountered from time to time in carrying out adequate maintenance at offshore for FPSO hulls that have been producing oil/gas at offshore for more than 20 years. If corrosion is left unchecked, the hull strength will fall below the required level, but any work to repair/reinforce the hull that involves the use of open flames will disrupt production, and bringing in the needed equipment/materials is no easy task. Given onboard crew limits, securing accommodation for the crew members responsible for repairs also presents challenges.
With such circumstances requiring the development of a new repair method whereby equipment/materials can be easily conveyed to the FPSO and cold repair work completed by a small number of personnel in a short time, MODEC has begun developing a repair method to restore hull strength to the necessary level by applying an engineering method known as vacuum assisted resin transfer molding (VaRTM): carbon fiber reinforced plastic (CFRP) is affixed to the steel material of the hull in those areas whose strength has been compromised by advancing corrosion.
The primary purpose of this repair method is to minimize the impact of repair work on production but, because limitation of work site and penalties for suspending production can also be avoided, major benefits can be expected for the project as a whole. MODEC has been conducting research and development on this repair method, including the use of VaRTM, in conjunction with Toray Industries, Inc.
VaRTM (Vacuum assisted Resin Transfer Molding) method
The VaRTM method is one of the method of producing a large FRP (fiber-reinforced plastic) structure which has been put to practical use with windmills and airframes. Based on this method, MODEC has been working to develop a method for repairing the steel plates of the hull with CFRP sheet.
Following is the process to repair the steel material of the FPSO hull:
- 1Attach the carbon fiber sheets on the steel structure with a strong adhesive, and put them in a bagging film.
- 2Inject liquid resin by infusion vacuum method to impregnate carbon fiber sheets with a resin.
- 3After the resin becomes hardened, remove the film
This method enables to raise the percentage of fiber contained in the CFRP and to provide high quality of repair service compared with Hand Lay-up method. Further, the method enable
By this method, CFRP, compared with the one by the Hand Lay-up method, has higher percentage of fiber content, and this will lead to high-quality repair service. Further, this method is suitable for the repair of FPSO/FSO hull because it completes the repair work in a short period..