phase 4 report - DNV

RN02: DESIGN OF FLOATING STRUCTURES IN ICE // PART 1 IntroductionBarents 20201. IntroductionThis report is the deliverable of Barents 2020Working Group RN02 “Design of stationary floatingunits against ice loads in the Barents Sea”. It consistsof four parts:1. Introduction with a brief history of the Barents2020 Project and earlier results of WorkingGroup RN022. A gap analysis performed by SDAG and Statoilthat has identified where amendments toISO 19906:2010 would be useful3. Background information that explains why theamendments are suggested and, in some cases,additional information that may be found useful4. A Guidance Document with recommendedadditions and amendments to ISO 19906:2010.1.1. Brief historyPhases 1 and 2Phase 1 of the project produced five Norwegian“position papers”, of which the one on Ice andMetocean conditions in the Barents Sea (Barents2020, 2008) is relevant for the work performed byWorking group RN02 in Phase 4. Phase 2 was apresentation of the “position papers” to the Russianpartners in December 2008, with which Phases 1 and2 ended.The report on ice and metocean recommendedthat the basis for possible changes/additions shouldbe ISO 19901-1 and ISO 19906. At that time,however, only an early draft of ISO 19906 wasavailable. The following topics were recommendedin the Norwegian “position paper” for a Russian-Norwegian working group in Phase 3 to achieveimprovements and/or additions to these standardsand codes:• Evaluation of the need for and suggest additionsregarding handling of uncertainties due tofew data, e.g. revised load/safety factors• Guidance/requirements on load combinations,in particular for ice in combination withmetocean (e.g. waves and bergy bits)• Narrow down ice load estimatesfrom different approaches• More ice load cases in one standard,e.g. critical load cases• Update Regional Description for Barents Seain the annexes to ISO 19901-1 and 19906• Evaluation of the need for and suggestadditions regarding data collection• Evaluation of which parts of NORSOK N-003can supplement ISO 19901-01, if any• Improving descriptions/guidance onicing, topside as well as hull, from seaspray and atmospheric conditions• Guidance on pipelines and sub-sea structureswhere ice scour may be expected• Additions regarding ice management inpack ice and from icebergs in pack ice• Consider the need for more specific guidanceon probabilistic methods when going into aregion where such methods have not been usedPhase 3In Phase 3 it was decided to narrow the topics inthe recommendations from Phase 1 and 2, anda working group, RN02, with the working title“Design of stationary offshore units against ice loadsin the Barents Sea” was established. This workinggroup consisted of Russian and Norwegian experts.The scope for Working Group RN02 was limited toloads coming from sea ice or glacial ice on stationaryunits and consisted of the following tasks:• Evaluate existing maritime and offshore oil andgas standards relevant for design of stationaryunits in the Barents Sea against ice loads;• Recommend standards for common use;• Propose recommended amendments and/or changes to the identified standards.• Stationary units/installations include:––Fixed structures, e.g. gravity basedand jacket installations––Floating units kept in position bymoorings or dynamic positioning,e.g. drilling and production vessels,spar and buoy shaped platforms.Sub-sea installations such as pipelines are excludedfrom this review.In Phase 3 the Working Group RN02 performeda joint Russian – Norwegian high level gap analysisof the most used Russian and Western standards andrules for ice loads against stationary structures.Report no 2012-0690 19