Summary
Allseas is one of the leading offshore pipeline installation contractors in the busi-ness. For the installation of pipes, it uses the so called S-lay method, a method where pipe sections are assembled into a continuous pipeline at the firing line, on-board the pipe lay vessel. Subsequent stations perform welding, non-destructive testing and coating tasks in this firing line.
Since the founding of the company in 1985, much of the equipment to perform these tasks was designed, developed and built in-house. A lot of effort was put into improving installation time. Allseas and its clients were mainly focused on the welding and NDT testing stations while the coating process drew relatively less attention.
In recent years the attention is shifted to the coating stations. There were also sig-nals that on some projects the process time of individual coating stations negatively affected the overall installation time.
Although some effort was made in the past to improve the coating process the re-sults were disappointing. The need for reducing overall process times while main-taining coating quality still remains. Therefore Allseas initiated this research, exploring possible changes to the coating process.
A preliminary research showed that fusion-bonded epoxy is the most used coating type. Based on that the choice was made to focus the research on the application process of fusion bonded epoxy.
The goal of the research was formulated as a research question: What are the possibilities to change the current process of field joint coating application, in order to achieve faster cycle times while maintaining the current coating quality, while taking into account requirements for changes to the process?
To answer the research question the current process of pipeline production was analysed. From this analysis it was concluded that there were three possibilities for changes to the process:
• The order of steps within the process • Combination of steps within the process • Alternative methods within the process step
A research into the current cycle times showed that for some projects the field joint coating stations could be critical. From the limited amount of data available it could be seen that the most time was used at the station where the joint is heated and coated. Analysis of cycle times did not show the surface preparation station to be critical. Interviews with Allseas employees however confirmed that for some projects the surface preparation station was critical.
The analysis of the current equipment used for the application process of fusion-bonded epoxy was done. This research showed that the current method of surface preparation, grit blasting, could be improved. The current method gives good results, but due to a limitation in space for the grit handling units it is difficult to optimise this method.
The method of heating the joint with induction heating is the most efficient and clean way. The shape of the coil however could be changed in order to combine the heating coil with other equipment.
A research into possible alternatives was done, based on the conclusions of the analysis of the current process and equipment. A number of possible alternatives were found.
The order of steps within the process:
• Pre-blasting with mechanical blasting followed by cleaning with laser or dry ice
• Pre-blasting with grit blasting followed by cleaning with laser or dry ice Combination of steps within the process:
• Shockwave Induced Spray Painting
• Combined Heat & Coat machine with alternative heating coil Alternative methods within the process step:
• Dry ice with grit blasting instead of grit blasting • Pick brush instead of grit blasting
• Low application temperature FBE instead of FBE
• Surface treatment with laser blasting instead of grit blasting
Based on found requirements for new equipment and the change of the process, a number of these alternatives were chosen to further research:
• Pre-blasting with mechanical blasting followed by cleaning with laser or dry ice
• Low application temperature FBE instead of FBE
• Surface treatment with laser blasting instead of grit blasting
Practical tests were performed to see whether these possible alternatives could lead to the reduction of cycle times while maintaining the coating quality. A test setup was designed and built in-house. The test setup replicated the process in the firing line. Steel plates were used, which were treated with the different surface treatment methods. After that they were heated in an industrial oven. After heating they were coated with FBE. Once the FBE was fully cured, destructive tests were performed to evaluate the level of the quality of the coating.
During the tests different measurements were taken. The time each of the surface treatment methods took was recorded. The noise levels of the surface treatment were recorded as part of the safety aspect. During the destructive test the degra-dation of the coating was measured.
Based on the test result it was concluded that there are three alternatives that can be identified as prominent alternatives for FBE application:
• Pre-blasting with mechanical blasting followed by cleaning with laser • Dry ice with grit blasting
• The application of LAT FBE
Based on the conclusions some further recommendations can be made for each of the three possible alternatives.
Pre-blasting with mechanical blasting followed by cleaning with laser:
• Research the possibilities for the incorporation of a mechanical blaster in the bevelling station
• Further test the use of laser equipment in the current process and with the current equipment
• Investigate possible safety issues related to the use of laser equipment Dry ice with grit blasting:
• Research the logistics of dry ice pellets
• Research the possibility of producing of dry ice on board the vessels • Execute more tests with different types of blast media added to the dry ice • Research the possibilities for the reduction of noise levels
• Investigate the possible safety issues with CO2 The application of LAT FBE:
• Research the possible time reduction when applying LAT FBE with current equipment
• Research the cost aspect of applying LAT FBE powder with respect to the reduction of time (cost versus gain)
