Project preparation and execution
“The power of preparation.”
A team of eight engineers worked throughout the summer to prepare all the required documentation for the project. As with many of Conbit’s project teams, it included a mix of structural and project engineers and draftsmen. Combining these skills is necessary to cover all the aspects of such an operation.
Planning and designing
During the early engineering stages, Conbit explored the feasibility and performed a structural analysis of the existing platform. Both results were positive and formed the basis for the initial design.
Conbit presented the initial plan and was approved by the client and the supplier of the two modules. Three months later, the team finished the detailed engineering. Next would be selecting the transport vessel.
Selecting the transport vessel
During the summer, representatives from Conbit and Mabruk met and reached a commercial understanding regarding the transport and installation phase. They decided that Conbit would be responsible from the moment the modules were on board a seagoing vessel (selected and contracted by Conbit) until the modules were installed on the BD-1 platform. Mabruk decided that the project should start at the Port of Rotterdam Authority, where the manufacturers of the modules would deliver.
During the first week of October, the M/V Industrial Kelly picked up the emergency shelter and the helideck. The vessel has its own cranes, which would be valuable when unloading in Tripoli. The modules were lifted two levels of the 130-meter long vessel.
The vessel arrived in Tripoli harbor in the middle of a public holiday week. The client managed to organize an efficient unloading slot despite the holiday.
The first crew to arrive in Libya embarked on a site survey. The four-man team spent seven days on the platform, during which they performed a dimensional verification and marked the locations where pad eyes were required.
The second crew traveled to the BD-1 just a couple of days before the emergency shelter, and the helideck arrived in Tripoli.
At the same time, half of the construction equipment was transported in offshore containers via Italy directly to the offshore location on the ASSO 31 supply vessel. Mabruk rented this supply vessel for the duration of the project. The customs authority and Conbit representative were present when the shipment arrived. The second shipment would arrive a week later on the platform.
Offshore lifting and installation
Immediately after the second crew arrived at the platform, the preparation works started. Scaffolding technicians started to place overboard scaffolding and perform the first welding activities.
At the end of the first week, the crew installed all the winch, sheave, and jacking frames and completed most of the preparatory welding. The team needed another week to prepare before lifting the emergency shelter. A small forklift brought onsite by Conbit proved very useful. This was equipped with a small lift boom and fitted into a 20-ft offshore container.
At the same time, the shore team on the quayside prepared the supply vessel. The works included the welding of D-Rings on the deck of the Almisan supply vessel. Besides the physical work, the onshore team completed the paperwork prior to the day of load out on the quayside. The final step on shore was to mobilize a 250-tonne crane, which was required to load the emergency shelter onto the supply vessel.
The lifting of the emergency shelter was scheduled for 30 October, when all the required manpower would be on board. Besides the Conbit team, the GL Marine Warranty Surveyor, Mabruk, and Total representatives would also be present on the BD-1 platform. The weather conditions should also meet the criteria for the lift. If all the signs were on green, the Almisan supply vessel would leave Tripoli to be under the platform four hours later.
The weather was looking hopeful on 30 October. The supply vessel bearing the emergency shelter could leave the port of Tripoli. It arrived at the DB-1 platform early morning. All load tests were successfully completed, and the green light was given to perform the lift of the new module.
With such a lift, the first few meters are critical. The waves move the vessel up and down, a movement that is independent of the lifting configuration on the platform. Once the lift begins, the load’s center of gravity moves below the lift point. This is observed by a vertical lift line, but even the slightest deviation can swing the load. The winch operator's skills and the vessel's captain were crucial to placing the emergency shelter exactly below the lift point. Once the lift line is vertical, the winch operator decides when to start lifting. Because the waves move the load up and down, the lift needs to start at the top of a wave. If the winch operator cannot start the lift at this precise moment, the vessel might rise and hit the load from the bottom. The winch operator must also lift at the top of the wave to prevent the load from slamming the sidewalls of the vessel if it starts to swing.
The required speed is precisely the reason why Conbit uses very fast lift winches. These can lift at a rate of 36 meters a minute with a capacity of 15 metric tonnes. For this project, the team deployed two of these winches. The winches are operated by a diesel-hydraulic powerpack, making the lifting configuration independent from the offshore platform utilities.
Hydraulic strand jacks performed the last part of the lift. These were positioned on top of custom-made jack frames and gradually took over the load from the lift winches. The secondary lift lines attached to the strand jacks performed the last part of the lift until the emergency shelter was in its final position. At the end of the day, the emergency shelter was secured in its final place.
The next day, the team removed the winches from the weather deck and assembled scaffolding for the side of the emergency shelter. This scaffolding provided the welders with the access to weld the interface connections. The weather deck was cleared for the next major activity during this work.
The helideck installation started with the assembly of the support frame. This frame would serve as the foundation of the helideck. On 1 November, the support frame was installed, and the helideck pancakes were loaded. The pancake was supplied in two halves; two halves are easier to transport, and one half was already nearing the maximum capacity of the deck crane of the BD-1 platform. The following day, the ASSO 31 transported the north pancake half offshore. During the journey, Conbit performed a load test on the deck crane. When the ASSO 31 arrived, the pancake half was lifted directly from the supply vessel onto the support frame. They repeated the same process for the other helideck half two days later.
The complete helideck and support frame had to be skidded into its final position, as the deck crane was unable to lift the pancake halves at this location. The team completed the work after skidding.
Conbit looks back at a successful project. The client supported Conbit’s alternative approach. The combination of solid engineering and a competent implementation team formed the basis for this success. During the actual implementation, we definitely proved the effectiveness of the concept. We thank all partners who contributed to this project. We would also like to express our appreciation to the client’s team for their support and cooperation in what was a challenging project in many ways.