Analisis Kelelahan dan Keandalan Rantai Tambat dengan Mempertimbangkan Beban Tandem Offloading dan Pengaruh Pretension

Shidqi, Hafizh Muhammad Naufal (2023) Analisis Kelelahan dan Keandalan Rantai Tambat dengan Mempertimbangkan Beban Tandem Offloading dan Pengaruh Pretension. Masters thesis, Institut Teknologi Sepuluh Nopember.

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Abstract

Rantai tambat adalah salah satu komponen yang penting di dalam industri oil and gas maupun industri maritim lainnya. Rantai tambat digunakan untuk mengamankan struktur seperti kapal maupun anjungan minyak dan gas terapung seperti FSO agar tetap berada di posisi yang ditentukan. Selama operasi rutin dan operasi bongkar muat (offloading), beban yang diberikan pada rantai tambat dapat menyebabkan kelelahan struktural sehingga terjadi kegagalan pada struktur. Oleh karena itu, analisis umur kelelahan dan keandalan pada rantai tambat sangat penting untuk memastikan keamanan dan kinerja yang optimal. Penelitian ini bertujuan untuk melakukan analisis kelelahan dan keandalan pada rantai tambat dengan mempertimbangkan dua faktor penting, yaitu pengaruh desain pretension dan pengaruh beban offloading. Beban offloading mengacu pada beban tambahan yang diberikan pada rantai tambat selama operasi bongkar muat dengan sistem tandem. Konfigurasi sistem tambat menggunakan sistem spread mooring sebanyak 8 rantai (4x2), berdiameter 87 mm, dengan variasi pretension 10%, 15% dan 20% dari Minimum Breaking Load (MBL) rantai. Dalam analisis kelelahan, metode "Rainflow Counting" dan "Palmgren-Miner" digunakan untuk menghitung jumlah siklus beban yang terjadi dan mengevaluasi akumulasi kerusakan akibat beban siklik sehingga nantinya umur kelelahan dapat dihitung dan diketahui. Sedangkan untuk analisis keandalan, digunakan meode Monte Carlo. Dari hasil penelitian didapatkan bahwa desain konfigurasi sistem tambat masih memenuhi persyaratan safety factor yang direkomendasikan oleh API RP 2 SK baik pada saat analisis SLS, ULS, maupun FLS. Pada kondisi SLS dan ULS, tension terbesar terjadi ketika FSO berada pada kondisi muatan ballast. Pada analisis kondisi FLS, didapatkan bahwa adanya beban offloading dapat menambah fatige damage sehingga mengurangi umur kelelahan pada rantai. Dengan frekuensi offloading sebanyak 24 kali per- tahun dan juga mempertimbangkan adanya pengaruh perubahan muatan selama offloading, didapatkan umur kelelahan paling sedikit terjadi pada chain 1.2 pada segmen splash zone, yaitu 71 tahun dengan safety factor 4.7. Keandalan chain 1.2 terhadap umur kelelahan pada target umur operasi 5, 10, dan 15 tahun adalah sebesar 99.89%, 97.67%, dan 90.32%.
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Mooring chains are an important component in the oil and gas industry and other maritime industries. Mooring chains are used to secure structures such as ships and floating oil and gas platforms such as FSOs to remain in their designated positions. During routine operations and offloading operations, the loads exerted on the mooring chain can cause structural fatigue resulting in failure of the structure. Therefore, fatigue life and reliability analysis on mooring chains is essential to ensure safety and optimal performance. This study aims to conduct fatigue and reliability analysis on mooring chains by considering two important factors, namely the influence of pretension design and the influence of offloading load. Offloading load refers to the additional load exerted on the mooring chain during tandem loading and unloading operations. The mooring system configuration uses a spread mooring system of 8 chains (4x2), 87 mm in diameter, with pretension variations of 10%, 15% and 20% from the Minimum Breaking Load (MBL) of the chain. In the fatigue analysis, the "Rainflow Counting" and "Palmgren-Miner" methods are used to calculate the number of load cycles that occur and evaluate the accumulated damage due to cyclic loads so that later the fatigue life can be calculated and known. As for the reliability analysis, the Monte Carlo method was used. From the research results, it is found that the mooring system configuration design still meets the safety factor requirements recommended by API RP 2 SK both during SLS, ULS, and FLS analysis. In SLS and ULS conditions, the largest tension value is when the FSO is in ballast load condition. In the FLS condition analysis, it is found that the offloading load can increase the fatige damage so as to reduce the fatigue life of the chain. With an offloading frequency of 24 times per year and also considering the effect of load changes during offloading, it is found that the least fatigue life occurs on chain 1.2 in the splash zone segment, which is 71 years with a safety factor of 4.7. The reliability of chain 1.2 against fatigue life at the target operating life of 5, 10, and 15 years is 99.89%, 97.67%, and 90.32%.

Item Type:	Thesis (Masters)
Uncontrolled Keywords:	keandalan, kelelahan, monte carlo, palmgren-miner, rainflow counting, rantai tambat, tandem offloading, reliability, fatigue, monte carlo, palmgren-miner, rainflow counting, mooring chain, tandem offloading.
Subjects:	T Technology > TC Hydraulic engineering. Ocean engineering > TC1680 Offshore structures
Divisions:	Faculty of Marine Technology (MARTECH) > Ocean Engineering > 38101-(S2) Master Thesis
Depositing User:	Hafizh Muhammad Naufal Shidqi
Date Deposited:	05 Aug 2023 14:59
Last Modified:	05 Aug 2023 14:59
URI:	http://repository.its.ac.id/id/eprint/102245

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