engleski

Interpretation of Results of Evaluation and Selection of Structural Elements for Survey of IRINA Platform

IRINA offshore platform is installed in the Croatian sector of the Adriatic Sea, in 48.0m water depth. The platform is designed as monopod supported by the frame structure with unmanned deck on three levels. Periodical controlling of the actual state of existing structures is a characteristic feature in structural check and health monitoring after initial loading or setting into the operation. Supervising and health monitoring of any kind of structure is a new field that has been opened to be of increasing importance with regard to control durability, stability and safety as well as to estimate the life span of structure. Different techniques are used to record the actual situation in order to get reliable information about on the on-site structure and structural elements. According to the task defied for the offshore platform IRINA 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 documents the « TECHNICAL REPORT FOR MONOPOD IN SERVICE ANALYSIS» and « DECK STRUCTURAL IN-SERVICE ANALYSIS» have been used, as a design project documentation of platform IRINA. 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 « Final Report Geotechnical Investigation – Annamaria A, Ana, Vesna and Irina Platforms Adriatic Sea» the design value of maximum ground acceleration Strength Level Earthquake SLE is set to value for the period of 200 years and Rare Intense Earthquake RIE for the period of 2000 years. According to API sections 17.5.3 and C2.3.6.c platform IRINA 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 medium and low risk. Volume of elaboration is 40 pages, contents of five sections, 27 figures and 2 tables, and referring to 23 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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