Analisis Cycle Fatigue Life pada Pipa Bawah Laut yang Mengalami Free Span dan Vortex-Induced Vibration

Uluumuddin, Ihsaan (2026) Analisis Cycle Fatigue Life pada Pipa Bawah Laut yang Mengalami Free Span dan Vortex-Induced Vibration. Other thesis, Institut Teknologi Sepuluh Nopember.

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Abstract

Pipa bawah laut memegang peranan strategis dalam distribusi minyak dan gas, namun sangat rentan terhadap permasalahan struktural seperti free span yang diakibatkan oleh ketidakrataan kontur dasar laut. Kondisi free span yang terpapar arus laut secara terus-menerus dapat memicu fenomena getaran akibat pusaran air atau Vortex-Induced Vibration (VIV), yang berpotensi memicu kegagalan lelah (fatigue failure) pada struktur. Penelitian ini bertujuan untuk menganalisis umur lelah (cycle fatigue life) pada pipa bawah laut yang mengalami free span dan VIV, dengan mengevaluasi pengaruh variasi panjang bentangan (5 m hingga 100 m) dan kecepatan arus laut (0,1 m/s hingga 1,2 m/s). Analisis dilakukan berdasarkan metode analitis standar DNV-RP-F105 dan divalidasi menggunakan simulasi numerik Computational Fluid Dynamics (CFD) serta Finite Element Analysis (FEA) berbasis perangkat lunak. Berdasarkan hasil penelitian, frekuensi natural pipa mengalami perubahan yang sejalan dengan panjang span dan kecepatan arus. Analisis cycle fatigue menunjukkan hubungan yang non-linear terhadap parameter-parameter tersebut. Nilai cycle fatigue terkecil yang mengindikasikan kerusakan paling cepat tercatat sebesar 2,14\times{10}^2 siklus pada kondisi span 60 m dengan kecepatan arus 1,2 m/s (tumpuan pinned-pinned). Sebaliknya, nilai cycle fatigue maksimum yang mampu ditahan struktur mencapai 7,39\times{10}^{14} siklus pada kondisi span 80 m dengan kecepatan arus 0,6 m/s (tumpuan fixed-fixed). Penelitian ini menyimpulkan bahwa panjang free span dan variasi kecepatan arus laut memberikan dampak yang sangat signifikan terhadap laju akumulasi kerusakan lelah pada infrastruktur pipa bawah laut.
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Subsea pipelines play a strategic role in oil and gas distribution but are highly susceptible to structural issues such as free spans caused by seabed irregularities. Prolonged exposure of a free-spanning pipeline to ocean currents can trigger Vortex-Induced Vibration (VIV), potentially leading to fatigue failure. This study aims to analyze the cycle fatigue life of a subsea pipeline subjected to free span and VIV by evaluating the effects of varying span lengths (5 m
to 100 m) and current velocities (0.1 m/s to 1.2 m/s). The analysis was conducted based on the DNV-RP-F105 standard analytical method and validated using numerical simulations, specifically Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) via software. The results show that the natural frequency of the pipeline is significantly dependent on the span length and current velocity. The cycle fatigue analysis reveals a non-linear
relationship with these parameters. The lowest cycle fatigue life was recorded at 2.14 × 102 cycles under a 60 m span and 1.2 m/s current velocity (pinned-pinned boundary condition), indicating a highly critical fatigue damage state. Conversely, the highest cycle fatigue life reached 7.39 × 1014 cycles under an 80 m span and 0.6 m/s current velocity (fixed-fixed boundary condition). This study concludes that the length of the free span and variations in
ocean current velocity have a highly significant impact on the accumulation of fatigue damage in subsea pipeline infrastructure.

Item Type:	Thesis (Other)
Uncontrolled Keywords:	free span, vortex induced vibration, subsea pipeline
Subjects:	T Technology > TC Hydraulic engineering. Ocean engineering > TC1665 Offshore structures--Materials.
Divisions:	Faculty of Marine Technology (MARTECH) > Ocean Engineering > 38201-(S1) Undergraduate Thesis
Depositing User:	Ihsaan Uluumuddin
Date Deposited:	21 Jul 2026 01:37
Last Modified:	21 Jul 2026 01:37
URI:	http://repository.its.ac.id/id/eprint/135964

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