This paper attempts to describe the development of "self-installed" decks on offshore platforms.
When North Sea operations first started platform installation was performed by means of conventional derrick barges i however, faced with harsh sea conditions, they did not prove very cost effective and installation was often delayed.
Thus, operators were driven to seek new concepts. Among them, TOTAL CFP, operator on the Frigg pipeline, chose to erect big cranes on bare platforms in order to complete installation. This concept soon proved to be a reliable one as it became far easier to take advantage of narrow windows of good weather than it would have been possible with derrick barges. Moreover, safety was increased.
After a few modifications, this installation scheme can be applied to a wide range of fixed platforms both in rough and calm seas.
In this paper, our intention is to explain why we chose this concept and to give the main results gained from our experience on the field.
Within the scope of the Frigg operations, TOTAL, as operator on the pipeline developed several completely new techniques which involved the installation of lifting devices with a load capacity of 300 t to 800 t on platforms.
Once developed by TOTAL and BUZZICHELLI, these techniques enabled offshore lifting operations to be carried out rapidly in weather conditions which were unsuitable for conventional lifting devices.
When operations first started in the North Sea, production platforms were equipped by means of conventional derrick barges.
The latter can work in up to half a foot heave but roll is critical, the limitation being between 0.5 and 1° depending on the size of the load. In the North Sea, these thresholds are often over-reached resulting in long waiting for calmer weather and sometimes in postponements of operations for up to 8 months, should they not have been completed before the winter season.
Moreover, safety is sometimes affected. Indeed, once a package has been lifted a cargo barge becomes very lively, which lead to a very tricky situation, as it is impossible to drop the package down either on the platform or back on the cargo barge. Should by any chance, the load then start swinging laterally, it is almost impossible to control.
Big modules and huge barges : some improvement but many disadvantages.
In an attempt to improve North Sea operations huge derrick barges appeared. They could handle large and heavy packages (up to 2 000 tons) in slightly worse sea conditions.
It was agreed that the bigger the modules, the fewer lifts required to install them. This was in fact quite true, but several disadvantages should be pointed out.
