Revised Rules On Mobile Offshore Rigs Issued By Det norske Veritas

Det norske Veritas has issued revised Rules for Classification of Mobile Offshore Units. The new edition supersedes the 1975-edition (with supplement of 1977).

The major changes from the previous edition are: More severe requirements to strength of steel structures. Residual strength is required to al- low for any damage in main structures which might avoid attention in time. The residual strength is also to be sufficient to withstand any external damage on main strength members caused by, e.g., a possible collision with a ship. The ability of the structures to withstand fatigue and development of cracks is given special attention.

The requirements to stability and floatability have been made more severe for the unit in intact as well as damaged conditions. Inclining tests are to be carried out also for sister units. Operational requirements have been added for bilge and ballast systems and emergency mooring of the unit in damaged condition. For accommodation units, additional floatability requirements have been stipulated with regard to damages of greater extent than assumed for drilling units.

The extent of the required periodical surveys for retention of class has been increased, especially for the two-yearly surveys.

In-service inspection programs are introduced to aid the surveyors in their efforts to do their jobs in the best possible way. The two-yearly surveys are normally to be carried out in sheltered waters. The four-yearly surveys are in all cases to be carried out in sheltered waters.

offshore requirements stability damages service development drilling members ballast