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Interpretation of Results of Evaluation and Selection of Structural Elemenets for Survey: Jacket, Boat Landing, Deck, Accomodation Module and Helideck, Katarina Platform

The Katarina Platform is installed in the Katarina Field located in the Croatian offshore of the Central Adriatic Sea in a water depth of 70.94 m. The platform is designed as temporarily manned platform that provides for a 13 man accommodation module (also termed as a living quarter’ s module) complete with an integrated helideck providing for platform access. The ability to detect changes in a structure in order to improve its reliability s going to be provide through periodical structural health monitoring. Scheduled manual inspections based on non-invasive damage detection techniques are used to continuously monitor components and, if necessary, to confirm decision for component repair and replacement. A minimum strength capacity of is considered appropriate for contemporary offshore platforms in order to provide a safety from any expected or unanticipated loads. Such provision also ensures a minimum standard for connections of particular members that take on primary importance in reserve strength assessments of the whole structure. Recording the actual situation is directed towards reliable information about on the on-site structure and particular structural element. According to the task defied for the offshore platforms Katarina, there was a request for selection of structural elements jacket & deck where it is necessary to perform monitoring and survey according to ISO standards ISO/CD 19902 and recommendations of American Petroleum Institute described in "API Recommended Practice 2A-WSD (RP 2A-WSD)", 21st ed., Dec. 2000. As the basic project documents and calculations for the platform Katarina "Jacket - Structural in Service Analysis", "Deck - Structural in Service Analysis" and "Accommodation Module & Helideck - Structural in Service Analysis" have been used. According to API Section 17.5.3, part 1, the assessment for seismic loading is not required for seismic zones 0, 1 and 2 due to, as specified in part 4 of same API Section, there was no significant level ground motions during platform exploitation. According to the technical documentation of the platform "Deck and Accommodation Module Dynamic & Seismic Analysis" the design value of maximum ground acceleration is set to value for the period of 200 years and for the period of 2000 years. According to API sections 17.5.3 and C2.3.6.c platform Katarina is inside seismic zone 2 where seismic loading is not a requirement in design level analysis if there was no significant seismic changes during exploitation. Procedure of survey of structural elements and criteria for their selection are transferred from ISO standards and API recommendations. Conclusions are supported by newest cognitions of the assessment of the offshore gas and oil platforms from the MMS workshop held on September 2003 in New Orleans. Minerals Management Service (MMS) is a bureau of U.S. Department of Interior, which ensures the safety and integrity of the existing structures, among others oil and gas platforms. The procedure of platforms assessment is described in this elaboration, including the selection of structural elements according to the defined criteria. Elements of platforms that need to be surveyed are sorted in tables in the groups of higher and low risk. Properties of particular elements and their global coordinates are not available in project documentation for platform Katarina, while their position is clearly determined in schematic layout of elements. Volume of elaboration is 46 pages, contents of seven sections, 38 figures and 4 tables, and referring to 25 papers and documents. Postulates that need to be emphasized are underlined due to better orientation in text.

offshore gas platform; survey; risk assessment; structural elements

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