Analisa Kelelahan Pada Proses Above Water Tie-In

Ra'fatul Jannah, Shabrina (2025) Analisa Kelelahan Pada Proses Above Water Tie-In. Other thesis, Institut Teknologi Sepuluh Nopember.

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Abstract

Seiring dengan meningkatnya permintaan energi global, instalasi pipa lepas pantai menjadi krusial untuk transportasi minyak dan gas. Metode Above Water Tie-In (AWTI) merupakan solusi yang efisien secara biaya untuk operasi penyambungan pipa di perairan dangkal. Namun, metode ini menghadirkan tantangan teknis yang signifikan, termasuk risiko tegangan berlebih, tekuk lokal (local buckling), kerusakan lapisan beton (concrete crushing), dan terutama kerusakan akibat kelelahan (fatigue damage) yang disebabkan oleh pembebanan siklik dari lingkungan laut. Penelitian ini bertujuan untuk melakukan analisis komprehensif terhadap integritas struktural dan umur kelelahan pipa berdiameter 20 inci selama proses instalasi AWTI. Analisis ini mencakup evaluasi tegangan, regangan, potensi local buckling, concrete crushing, serta penentuan waktu tunggu operasional (holding time) yang aman, dengan mengacu secara ketat pada standar DNVGL-ST-F101. Sembilan skenario operasional dianalisis, yang merupakan kombinasi dari variasi tahapan instalasi (lifting dan lowering-shifting), kondisi internal pipa (empty dan flooded), serta kondisi pasang surut air laut. Kerusakan kelelahan dievaluasi menggunakan metode rainflow counting untuk identifikasi siklus tegangan dan aturan akumulasi kerusakan linier Palmgren-Miner. Hasil analisis menunjukkan bahwa skenario lowering-shifting dengan pipa dalam kondisi kosong merupakan kondisi pembebanan paling kritis, yang menghasilkan tegangan maksimum sebesar 311.915 kPa (99,59% dari SMYS) dan regangan maksimum 0,163%. Verifikasi terhadap tekuk lokal menghasilkan nilai Unity Check (UC) tertinggi sebesar 0,998, yang menunjukkan margin keselamatan yang tipis. Meskipun demikian, seluruh kriteria integritas struktural dasar telah terpenuhi. Analisis kelelahan menghasilkan umur kelelahan paling kritis selama 85,98 jam dan yang terpanjang selama 6.550,63 jam, di mana semua skenario yang dianalisis berhasil melampaui kriteria waktu tunggu operasional minimum industri selama 72 jam. Berdasarkan temuan ini, disimpulkan bahwa proses instalasi pipa menggunakan metode AWTI untuk studi kasus ini dinyatakan aman dan layak secara teknis.
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With the increasing global energy demand, offshore pipeline installation has become crucial for oil and gas transportation. The Above Water Tie-In (AWTI) method is a cost-efficient solution for shallow water pipeline connection operations. However, this method presents significant technical challenges, including the risks of overstress, local buckling, concrete crushing, and especially fatigue damage caused by cyclic loading from the marine environment. This study aims to conduct a comprehensive analysis of the structural integrity and fatigue life of a 20-inch diameter pipeline during the AWTI installation process. The analysis includes evaluation of stress, strain, potential local buckling, concrete crushing, and determination of safe holding time, strictly referring to the DNVGL-ST-F101 standard. Nine operational scenarios were applied, which are a combination of various installation stages (height and shear), internal conditions of the pipeline (empty and flooded), and tidal conditions. Fatigue damage was evaluated using the stress cycle freezing rainflow calculation method and the Palmgren-Miner linear damage accumulation rule. The analysis results show that the loweringshifting scenario with the pipe in an empty condition is the most critical loading condition, which produces a maximum stress of 311,915 kPa (99.59% of SMYS) and a maximum strain of 0.163%. Verification of local buckling produces the highest Unity Check (UC) value of 0.998, indicating a thin safety margin. Nevertheless, all basic structural integrity has been met. Fatigue analysis produces the most critical fatigue life of 85.98 hours and the longest fatigue life of 6,550.63 hours, where all solved scenarios successfully exceed the industry minimum operational waiting time criteria of 72 hours. Based on these findings, it is concluded that the pipe installation process using the AWTI method for this case study is declared safe and technically feasible

Item Type:	Thesis (Other)
Uncontrolled Keywords:	Above Water Tie-In, DNVGL-ST-F101, Analisis Kelelahan Above Water Tie-In, DNVGL-ST-F101, Fatigue Analysis
Subjects:	T Technology > TA Engineering (General). Civil engineering (General) > TA418.38 Materials--Fatigue. 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:	Shabrina Ra' Fatul Jannah
Date Deposited:	21 Jul 2025 08:07
Last Modified:	21 Jul 2025 08:07
URI:	http://repository.its.ac.id/id/eprint/120322

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