Offshore jacket platforms are designed to fulfil their intended purpose in oil and gas exploitation at designated service life periods. During the operational development, a number of field operators extend their platform service life if the reserves are still available. This technical paper proposes the method to assess the structural integrity of several aging platforms in a field with a simplified approach. Taking the case of “B” Field platforms installed in the mid-1990s, the detailed procedure and example are discussed thoroughly. Five indicators furnished with quantification procedures are also presented to propose the ranking methodology. This paper also proposes the method of jacket platforms grouping based on several similarity criteria. The results of this approach can be used as a baseline for more detailed structural integrity assessment for each group representation.

Recent years have shown the increasing number of SPAR offshore floating platforms built and delivered worldwide. This eventually is strongly related to the generic potential of such platforms, in term of economy and performance aspects, especially for the operation in deep water. For operation in harsh sea environment previous SPAR investigations suggested the addition of heave plate on its keel to enhance the heave motion quality. This paper reports an experimental study conducted on SPAR model, scaled 1: 125 from the full size, installed with a heave plate sized 1.3 of hull diameter. Results of the study demonstrate the additional of heave plate may reduce the heave reaction force due to wave excitation approximately 35% in comparison with that without heave plate. This in turn leads to the decreasing of heave response by as much as 54%. Evaluations suggest the reductions in heave reaction force and response are induced by the escalation of heave damping in the order of 49% generated by the heave plate. The experimental results are well verified by the outcomes of computations based on analytical method and strip theory.

Offshore structure, particularly fixed offshore structures, should be kept in the performance for the fit-for-purpose condition during their operating lifetime. For fixed offshore structures that exceed their designated life years, the proper Structural Integrity Management System (SIMS) should be developed and applied. Despite the fixed offshore platforms have their service life, there are still platforms that continue to operate exceeding their service lifetime. These ageing platforms should be taken care thoroughly to avoid the consequences that could take casualties. This paper will propose the proper initiation of SIMS development for ageing fixed offshore platforms in Indonesia, by taking an example at Bekapai Field Platforms in East Kalimantan. Using HAZID technique and several ranking criteria, the platforms are assessed and ranked. Platforms that categorized in critical condition are grouped based on similarities in geometry and function. The highest rank is analyzed in computer Finite Element Analysis (FEA) Software with modification based on latest inspection result. This method is proven to be a proper method to be used as a maintenance program for ageing fixed offshore platforms in Indonesia.

This paper uses an analytical method to examine the motion of a Tension Leg Fish Cage (TLFC) in regular and random waves. TLFC is a conceptual design of a fish cage based on the Tension Leg Platform (TLP) working principle that is usually used in deep water offshore oil and gas exploration. The idea of providing a safe environment to combine ecotourism and fish farming in a single platform led us to perform an analytical calculation to assess the possibility of using the TLP concept in fish farming. A preliminary conceptual design of TLFC using an HDPE floater with steel cable tendon is presented. The analytical calculation of the response amplitude operator for surge and heave motion is presented using linear airy wave theory with head seas encountering angle. This paper also presents the calculation of TLFC surge and heave motion under random wave loads. The random wave spectra used in this paper are JONSWAP and ISSC spectra. The result shows that the surge and heave motion response of TLFC is relatively small and, therefore, can be analyzed further with more detailed consideration. It is admitted that HDPE is a brittle material that cannot sustain any long period of constant tension. Hence the optimum tendon-floater connection for the structure is subject to further research.

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