Analisis Umur Kelelahan Mooring Chain Pada Sistem Tambat CALM Buoy Dengan Penurunan Diameter Karena Korosi

Sari, Giskha Yuanita Devita (2026) Analisis Umur Kelelahan Mooring Chain Pada Sistem Tambat CALM Buoy Dengan Penurunan Diameter Karena Korosi. Other thesis, Institut Teknologi Sepuluh Nopember.

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Abstract

Floating Storage and Offloading (FSO) merupakan fasilitas terapung yang membutuhkan sistem tambat untuk mempertahankan posisi saat beroperasi di laut terbuka. Salah satu sistem yang bisa digunakan adalah Catenary Anchor Leg Mooring (CALM) Buoy, yang bekerja melalui konfigurasi rantai tambat untuk menahan beban dinamis akibat angin, arus, dan gelombang. Dalam lingkungan laut, permasalahan rantai tambat tidak hanya menerima pembebanan dinamis secara berulang, tetapi juga mengalami penurunan ketebalan akibat korosi. Penurunan ketebalan akibat korosi menyebabkan pengurangan diameter efektif rantai tambat, sehingga berpengaruh terhadap mengecilnya nilai Minimum Breaking Load (MBL) dan meningkatnya respons tegangan pada rantai. Dengan demikian, kombinasi antara beban dinamis dan korosi akan menjadi faktor penting yang dapat menurunkan umur kelelahan rantai tambat. Penelitian ini bertujuan menganalisis pengaruh korosi terhadap umur fatigue rantai tambat dengan melakukan peninjauan tiga kondisi operasi, yaitu kondisi nominal tanpa korosi untuk selama 1 (satu) tahun, kondisi dengan tingkat korosi 0,4 mm/tahun untuk selama 1 (satu) tahun, dan kondisi dengan tingkat korosi 0,4 mm/tahun untuk selama 30 tahun. Peninjauan kelelahan rantai tambat dikaji untuk tiga variasi kondisi muatan FSO, yakni full load, half load, dan ballast load. Perhitungan fatigue dilakukan dengan menggunakan metode Combined Spectrum dan pendekatan kurva T-N memakai safety factor 3. Tahapan perhitungan diawali dengan mengolah hasil analisis dinamis untuk memperoleh parameter standar deviasi dan zero-up-crossing period (Tz) dari respon effective tension setiap mooring line sebagai dasar perhitungan fatigue damage. Nilai damage pada setiap kombinasi kondisi muatan, arah gelombang, dan sea state dikalikan dengan probabilitas kejadian dari wave scatter untuk memperoleh annual fatigue damage. Hasil analisis menunjukkan bahwa chain-4 merupakan mooring line paling kritis karena menerima beban lingkungan secara in-line dengan probabilitas kejadian dominan sebesar 18,84%. Hasil perhitungan umur fatigue minimum pada kondisi nominal adalah 102,16 tahun. Pada kondisi korosi 0,4 mm/tahun, umur fatigue menurun menjadi 99,08 tahun atau berkurang 3,01% dari kondisi nominal. Pada kondisi proyeksi korosi 30 tahun, umur fatigue menurun menjadi 41,05 tahun atau berkurang 59,82% bila dibandingkan dengan kondisi nominal. Hasil ini menunjukkan bahwa korosi jangka panjang berpengaruh signifikan terhadap penurunan umur fatigue. Namun nilai umur fatigue minimum masih lebih besar dari design life operasional yang ditetapkan, sehingga sistem tambat CALM Buoy masih memenuhi kriteria keamanan terhadap kegagalan fatigue.
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Floating Storage and Offloading (FSO) is a floating facility that requires a mooring system to maintain its position during operation in open sea conditions. One mooring system that can be used is the Catenary Anchor Leg Mooring (CALM) Buoy, which operates through a mooring chain configuration to withstand dynamic loads induced by wind, current, and waves. In the marine environment, mooring chains are not only subjected to repeated dynamic loading but also experience thickness reduction due to corrosion. Corrosion-induced thickness reduction decreases the effective diameter of the mooring chain, thereby affecting the reduction of the Minimum Breaking Load (MBL) and increasing the tension response in the chain. Therefore, the combination of dynamic loading and corrosion becomes an important factor that can reduce the fatigue life of mooring chains. This study aims to analyze the effect of corrosion on the fatigue life of mooring chains by considering three operating conditions, namely the nominal condition without corrosion for 1 (one) year, the condition with a corrosion rate of 0.4 mm/year for 1 (one) year, and the condition with a corrosion rate of 0.4 mm/year projected over 30 years. The fatigue assessment of the mooring chain was conducted for three variations of FSO loading conditions, namely full load, half load, and ballast load. Fatigue calculations were performed using the Combined Spectrum method and the T-N curve approach with a safety factor of 3. The calculation procedure began by processing the results of dynamic analysis to obtain the standard deviation and zero-up-crossing period (Tz) parameters from the effective tension response of each mooring line as the basis for fatigue damage calculation. The damage value for each combination of loading condition, wave direction, and sea state was then multiplied by the occurrence probability from the wave scatter diagram to obtain the annual fatigue damage. The analysis results show that chain-4 is the most critical mooring line because it receives environmental loading in an in-line direction with a dominant occurrence probability of 18.84%. The minimum calculated fatigue life under the nominal condition is 102.16 years. Under the corrosion condition of 0.4 mm/year, the fatigue life decreases to 99.08 years, representing a reduction of 3.01% compared to the nominal condition. Under the 30-year corrosion projection condition, the fatigue life decreases to 41.05 years, representing a reduction of 59.82% compared to the nominal condition. These results indicate that long-term corrosion has a significant effect on the reduction of fatigue life. However, the minimum fatigue life remains greater than the specified operational design life; therefore, the CALM Buoy mooring system still satisfies the safety criteria against fatigue failure.

Item Type:	Thesis (Other)
Uncontrolled Keywords:	CALM Buoy, Mooring Chain, Korosi, Penurunan Diameter, Umur Kelelahan,CALM Buoy, Mooring Chain, Corrosion, Diameter Reduction, Fatigue Life
Subjects:	V Naval Science > VM Naval architecture. Shipbuilding. Marine engineering > VM161 Ships--Hydrodynamics
Divisions:	Faculty of Marine Technology (MARTECH) > Offshore Engineering > 54040-(S1) Undergraduate Thesis
Depositing User:	Giskha Yuanita Devita Sari
Date Deposited:	21 Jul 2026 06:31
Last Modified:	21 Jul 2026 06:31
URI:	http://repository.its.ac.id/id/eprint/136078

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