TWISTLOCKS IN MODULAR OFFSHORE PLATFORM DESIGNS FOR THE ARCTIC

Melting sea ice opens new possibilities for shipping routes and gas production in the Arctic. The project POLAR (Production, Operations and Living in Arctic Regions) represents a cooperation between industry and university to develop a concept for LNG production including the development of an ice-going LNG carrier and a LNG offshore platform which will operate in the Russian Arctic.

The task of the University of Rostock is to assess the usability of twistlock systems to mount auxiliary modules on offshore platforms in arctic regions and to generate dimensioning equations to calculate the strength of these mountings. If a twistlock system is used for non-standard applications, the existing rules are not applicable. Thus, a different design approach has to be taken.

A series of finite element analyses has been presented to identify the most important influence factors for the use of twistlocks under different non-standard loading conditions. Dimensioning equations have been derived by parameter studies for typical cases of intended non-standard use such as mountings of portable deck cranes on offshore platforms for the arctic. These equations depend on the roll angle of the platform and the friction coefficient between the contact areas in the twistlock system.

The ultimate strength analyses - leading up to the collapse of the twistlock - are conducted to assess the safety margin between elastic design and final rupture. In addition, experimental assessments are carried out. In these experiments, combinations of twistlocks and container corner castings are subjected to cyclic loads, long-term tensile load at design level and ultimate loads. The experimental results will be used for validation of the design equations, finite element collapse analyses and the general functionality of twistlocks in non-standard use. The experiments are conducted with a heavy duty hydraulic test rig. The results of the study are an important step to ensure the structural and functional integrity of twistlocks in non-standard use under arctic conditions.