Solid ballast in double bottom tanks Lorelay
Project scope
The dynamically positioned pipe lay vessel Lorelay will be modified to accommodate for new projects. Amongst other modifications, heavy ballast will be installed for improving the vessel’s stability, replacing current steel ballast (pipes, plates, bars) and concrete piles, placed in the hold.
Conditions
The heavy ballast will be installed in double bottom tanks 1C and 3C, located underneath the cargo hold amidship. Minimum mass to be installed in Tank 1C is 2,079 tonnes, spread over ~210 interconnected compartments. For 3C minimum installed mass is set at 2,401 tonnes, spread over ~165 interconnected compartments. Initial minimum target density of the ballast slurry is 3,675 kg/m3 at a fill rate of 98% (v/v).
Lorelay situated in a dry dock, with limitations for equipment setup, as we have to deal with available space close to the dock and on-site mixing of aggregates. Access of Lorelay is located roughly 8m above pump level and tanks are located 15m below access level. On average 1 filling point per 9 interconnected compartments.
Milestones
- Preparation and testing of 99 ballast compositions, including the selection of the most suitable raw materials
- 1:10 scale model test, including scaling down the raw materials, as well as a pump simulation
- Full scale test to determine the exact ballast composition and pump settings
- Final installed mass: 2,400 tonnes in Tank 3C and 2,076 tonnes in tank 1C
- Slurry pumped through a total pipe length of 177m for tank 3C and 144m for tank 1C
- Capricious project planning crawling further and further to end of the docking window
- Average measured slurry density is 3,770 kg/m3 (235.35 lb/ft3) at an average slump flow of 538 mm
- Fill rate (v/v) 95.5%
- Average pace 11,5 m3/hr gross – maximum pace 21,8 m3/hr net
- Gross installation time for tank 1C is 40h11m56s and for tank 3C is 63h22m55s
- Slurry in 177m of steel pipe (12.2 liter slurry per meter pipe) is still pumpable after 3 hours downtime
