Page 64: of Offshore Engineer Magazine (Sep/Oct 2015)

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LAM 28 platform, operated by DOTL, located in the Caspian Sea, approx. 25-35km west ofshore Cheleken peninsula, Turkmenistan.

environmental conditions exceeding the drag contribution, it is accepted that target life extension of 10 years. The one the platform is actually capable of the maximum yearly load is reached in reassessment showed that the platform withstanding. relation to the maximum annual wave was compliant with the required safety

We get to those probabilities by the height. It is assumed that the calculated level for the desired extension life required safety target, which can be values of the environmental forces are target, provided that the platform shall related to the actual system capacity of characterized by a yearly probability of be evacuated, and subsequently subject the platform, measured by the residual exceeding equal to those of the associated to a special survey, in case that a sea strength reserve of the whole jacket. That wave height. state characterized by maximum wave is evaluated in the simplifed system reli- In order to solve the reliability evalu- height greater than or equal to about ability assessment introduced by RINA ation, it is useful to evaluate the statisti- 10m happens. for the certifcation of the life extension cal distribution of the environmental We used the same system to determine of many offshore platforms in different load extremes according to a lognormal the expected life of the Nenè platform offshore areas. distribution, since it allows solving of the that had been used in the Gulf of Mexico

RINA uses elasto-plastic analysis reliability evaluation in a simple closed for 10 years and was then to be modifed linked to statistical evaluation. The struc- form. An evaluation of the approximation and installed on a new site off Congo. tural model is subject to environmental introduced in relation to this assumption The analysis with the structural modif- loads, which increase up to the whole has been made in a joint industry project cations and new site conditions showed system collapse. The statistics then take carried out by Italian offshore operators that an in-service life with acceptable into account strength and the environ- relevant to the life extension of existing safety levels of 10 years was obtainable mental load, in order to fnally evalu- offshore structures in the Adriatic Sea without strengthening. ate the yearly probability of collapse in and it has been shown as negligible for storm conditions. the fnal result. Stefano Copello is

A notional yearly probability of col- The reserve strength ratio and its rela- product development lapse of the platform may be evaluated by tionship to the target values of notional manager at RINA a simplifed procedure, starting from the yearly probability of failure can then be Services. He gradu- evaluation of the environmental forces calculated. Note that there are guidelines ated with frst class acting on the structure, corresponding to on what this ratio should be in the ISO honors in civil wave, current and wind conditions with standards for new platforms, but these engineering at return period of one-year and 100 years, can be reduced for life extension so there Università degli Studi which may be represented by one-year is no set acceptable answer. di Genova. At RINA since 1991, he has and 100 years base shear global values RINA used this approach for the LAM worked on technical activities inherent to determined by the quasi-static analysis 28 platform offshore Turkmenistan in the design, construction and installation normally carried out for the in-place 27m water depth, consisting of different of offshore structures, with particular conditions of the platform. simple jacket modules joined at their reference to safety, reliability and

Then, for steel truss offshore struc- topside by a latticed module support maintenance problems of fxed offshore tures, where the hydrodynamic load in frame. This platform was subject to a platforms and the development of storm conditions is dominated by the reassessment analysis in 2013 with a reliability tools.

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