Fatigue Life Analisis Pressure Hull Submersible Vehicle Dengan Mempertimbangkan Pengaruh Faktor Korosi Dan Kampuh Las Yang Berbeda

Pambudi, Arif (2026) Fatigue Life Analisis Pressure Hull Submersible Vehicle Dengan Mempertimbangkan Pengaruh Faktor Korosi Dan Kampuh Las Yang Berbeda. Doctoral thesis, Institut Teknologi Sepuluh Nopember.

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Abstract

Integritas operasional submersible vehicle di bawah tekanan hidrostatik ekstrem sangat bergantung pada pressure hull sebagai struktur penahan beban utama. Namun, lingkungan laut yang agresif dan siklus pembebanan berulang memicu degradasi struktural akibat interaksi simultan dari korosi melingkar pada penetrasi snorkel flap, pitting corrosion pada kulit hull, serta cacat akar las pada sambungan seksi blok. Kombinasi cacat lokal ini melemahkan kekakuan struktur dan memicu Low Cyclic Fatigue (LCF) di bawah fluktuasi tekanan hidrostatik laut dalam. Penelitian ini bertujuan untuk menganalisis efek penipisan pelat akibat korosi penetrasi, pitting corrosion, dan variasi kampuh las terhadap kekuatan struktur dan sisa usia pakai (remaining fatigue life) pressure hull. Analisis dilakukan dengan metode Elemen Hingga (Finite Element Method/FEM) pada kedalaman operasional 50 m, 100 m, 150 m, 200 m, dan 250 m untuk mengevaluasi parameter total deformation, equivalent stress, fatigue life, dan safety factor. Hasil simulasi FEM menunjukkan bahwa integrasi ketiga faktor cacat tersebut memicu penurunan kekakuan dan kenaikan stress concentration factor sebesar 28% pada persimpangan frame dan penetrasi snorkel flap. Kondisi ini meningkatkan total deformation maksimum sebesar 31,82%–38,82% (6,904 mm di 50 m hingga 31,479 mm di 250 m) serta menyebabkan Equivalent Von-Mises stress melampaui batas luluh baja HY-80 (σ yield ~ 550 MPa) mulai kedalaman 50 m (273,27 MPa) hingga 250 m (1.423,30 MPa). Berdasarkan kriteria Soderberg, terjadi degradasi fatigue life ekstrem hingga 100%, di mana ketahanan lelah struktur turun dari 2.000.000 siklus pada kedalaman 50 m menjadi 47.668 siklus pada kedalaman 100 m dan selanjutnya menjadi 0 siklus mulai kedalaman 150 m. Evaluasi terhadap standar DNV-GL (2018) mengonfirmasi bahwa pressure hull terdampak gagal memenuhi syarat keselamatan (safety factor 2,013–0,386, di bawah standar minimum DNV-GL 2,92–1,88) serta gagal memenuhi ambang batas minimum ketahanan lelah 10.000 siklus pada kedalaman ≥150 m akibat masuknya struktur ke dalam rezim Low Cycle Fatigue (LCF) kritis.
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The operational integrity of a submersible vehicle under extreme hydrostatic pressure depends heavily on the pressure hull as the primary load-bearing structure. However, the aggressive marine environment and cyclic loading trigger structural degradation driven by the simultaneous interaction of circumferential corrosion at the snorkel flap penetration, pitting corrosion on the hull shell, and weld root defects at section-block joints. The combination of these local defects compromises structural stiffness and accelerates Low Cycle Fatigue (LCF) failure under deep-sea hydrostatic pressure fluctuations. This study aims to analyze the effects of plate thinning caused by penetration corrosion, pitting corrosion, and weld joint misalignments on the structural strength and remaining fatigue life of the pressure hull. Finite Element Method (FEM) analysis was performed at operational depths of 50 m, 100 m, 150 m, 200 m, and 250 m to evaluate total deformation, equivalent stress, fatigue life, and safety factors. The FEM simulation results demonstrate that the integration of these three defect factors induces a reduction in structural stiffness and an increase in the stress concentration factor of up to 28% at the frame and snorkel flap penetration intersection. This condition leads to an increase in maximum total deformation ranging from 31.82% to 38.82% (from 6.904 mm at 50 m to 31.479 mm at 250 m) and causes the Equivalent Von-Mises stress to exceed the yield limit of HY-80 steel (σ yield ~ 550 MPa) across depths from 50 m (273.27 MPa) to 250 m (1,423.30 MPa). Based on the Soderberg fatigue criterion, an extreme fatigue life degradation of up to 100% occurs, where structural fatigue endurance drops sharply from 2,000,000 cycles at a depth of 50 m to 47,668 cycles at 100 m, reaching 0 cycles from 150 m onward. Evaluation against DNV-GL (2018) standards confirms that the damaged pressure hull fails to meet safety criteria (safety factor between 2.013 and 0.386, falling below the required minimum standard of 2.92 to 1.88) and fails to satisfy the minimum fatigue endurance threshold of 10,000 cycles at depths ≥150 m due to the structure entering a critical Low-Cycle Fatigue (LCF) regime.

Item Type:	Thesis (Doctoral)
Uncontrolled Keywords:	pressure hull, fatigue life, korosi, kampuh las yang berbeda, pressure hull, fatigue life, corrosion, weld joint misalignments
Subjects:	T Technology > TA Engineering (General). Civil engineering (General) > TA418.38 Materials--Fatigue.
Divisions:	Faculty of Marine Technology (MARTECH) > Marine Engineering > 36001-(S3) PhD Theses
Depositing User:	Mr. Marsudiyana -
Date Deposited:	10 Aug 2026 04:16
Last Modified:	10 Aug 2026 04:16
URI:	http://repository.its.ac.id/id/eprint/144283

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