The new international code ISO 19906 "Petroleum and natural gas industries - Arctic offshore structures" [1] was published in December 2010 after more than nine years of development. ISO 19906 uses the limit states design approach. Compliance is based on ensuring that the action effects arising from each factored action combination do not exceed factored resistances. The partial action factors have been calibrated to reliability targets. This paper describes the philosophy behind the quantification and use of the reliability targets, the definition of the limit states and action combinations, the philosophy of principal and companion environmental actions, and how the calibrated values of the action factors were incorporated in the action combinations.
The new ISO 19906 has been developed in Working Group 8 (WG8) of ISO Technical committee TC67/SC7 "Offshore structures". Experts from all arctic nations and from most other nations involved in the design of offshore structures in arctic and cold regions participated in WG8. Consequently, all the arctic nations and all European nations have undertaken to adopt ISO 19906 into their sets of national standards, and ISO 19906 is expected to be adopted worldwide for design of arctic offshore structures. This paper explains the design approach and underlying structural reliability levels in order to assist with application of the code in different ice covered environments and regulatory jurisdictions.
Reliability targets for arctic offshore structures have been used to calibrate the values of partial action factors for use in limit states action combinations, with particular focus on environmental actions arising from sea-borne ice, see Maes and Thomas [2] and OGP report 422 [3]. If these partial action factors are applied to Ultimate Limit State (ULS) and Abnormal (Accidental) Limit State (ALS) action combinations and the resulting action effects do not exceed factored resistances, the reliability targets are deemed to be achieved
"Reliability Target" as used in ISO 19906 is expressed as an annual probability of failure which is associated with global structural failure or with component failure leading to global structural failure. In common with the other ISO codes for offshore structures, namely ISO 19900 [4] and its associated standards, commonly known as the ISO 19900-series, ISO 19906 considers both life-safety and environmental protection through specifying three exposure levels, L1, L2 and L3, as defined in ISO 19902. [5].
