Sabila, Annisa (2026) Analisis backflow dengan fault tree analysis (FTA) pada boiler feed water system di industri LNG Bontang. Diploma thesis, Institut Teknologi Sepuluh Nopember.
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Abstract
Boiler Feed Water Pump (BFWP) merupakan peralatan kritis pada sistem pembangkit tenaga di industri LNG yang berfungsi menyuplai air umpan dari deaerator menuju boiler. Keandalan BFWP sangat bergantung pada efektivitas sistem proteksi aliran minimum untuk mencegah kondisi low flow yang dapat menyebabkan overheating dan kavitasi. Automatic Recirculation Valve (ARC Valve) digunakan sebagai perangkat utama proteksi minimum flow, namun data historis kegagalan menunjukkan bahwa ARC Valve merupakan komponen dengan tingkat kegagalan tertinggi dan berkontribusi terhadap terjadinya backflow yang mengakibatkan pompa burn out. Meskipun telah dilakukan modifikasi dengan penambahan check valve pada jalur resirkulasi, kejadian backflow masih berpotensi terjadi dan disertai peningkatan kegagalan pada komponen proteksi tambahan. Kondisi ini mengindikasikan bahwa solusi yang ada belum mampu mengendalikan risiko secara menyeluruh. Oleh karena itu, penelitian ini bertujuan untuk menganalisis penyebab kegagalan backflow pada sistem BFWP serta mengusulkan rekomendasi solusi untuk mengeliminasi kegagalan pada risiko paling rendah (insignificant risk). Metodologi penelitian diawali dengan analisis kegagalan backflow. Selanjutnya dilakukan Fault Tree Analysis (FTA) untuk menyusun struktur logis kegagalan, mengidentifikasi events yang berkontribusi, serta menentukan Minimal Cut Sets (MCS) dan critical events yang paling dominan. Setelah mengetahui critical events, maka dianalisis lebih lanjut menggunakan Five Whys untuk critical events tertinggi hingga terendah. Hasil penelitian menunjukkan bahwa ARC Valve dan check valve merupakan komponen paling kritis dengan nilai SID sebesar 0,7369, diikuti oleh komponen pompa sebesar 0,2344. Keandalan ARC Valve itu sendiri sangat bergantung terhadap fungsi internal part, yaitu fungsi check valve, modulasi, flow sensing, dan reduksi tekanan. Apabila salah satu fungsi tersebut gagal dapat menyebabkan kegagalan fungsi ARC Valve. Sementara itu, kegagalan pompa juga diidentifikasi lebih lanjut karena fluktuasi operasi pompa sangat memengaruhi operasional ARC Valve. Hal ini dikarenakan ARC Valve merupakan jenis pilot valve yang aktuasinya dipengaruhi oleh fluida kerjanya. Kegagalan pada pompa itu sendiri disebabkan oleh penurunan daya hidrolik akibat dari reduced pressure atau reduced capacity atau no discharged. Bisa juga karena daya hidrolik pompa hilang sama sekali akibat dari trip sistem atau kegiatan maintenance rutin. Berdasarkan hasil analisis, direkomendasikan program inspeksi internal ARC Valve setiap dua tahun serta penambahan lapisan proteksi melalui redesain sistem untuk mengendalikan risiko backflow dan reverse rotation sehingga keandalan operasional BFWP dapat ditingkatkan. Penambahan dua lapisan proteksi (yaitu surge tank dan one way clutch) dapat menurunkan pelsuang kegagalan menjadi 10^6 per tahun (kategori risiko insignificant).
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The Boiler Feed Water Pump (BFWP) is a critical piece of equipment in the power generation system of the LNG industry, serving to supply feed water from the deaerator to the boiler. The reliability of the BFWP heavily depends on the effectiveness of the minimum flow protection system to prevent low-flow conditions that can cause overheating and cavitation. The Automatic Recirculation Valve (ARC Valve) is utilized as the primary minimum flow protection device. However, historical failure data indicate that the ARC Valve has the highest failure rate and contributes to backflow occurrences that lead to pump burnout. Although modifications have been made by adding a check valve to the recirculation line, backflow events may still occur and are accompanied by an increase in failures of the additional protection components. This condition indicates that the existing solutions have not comprehensively mitigated the risk. Therefore, this study aims to analyze the root causes of backflow failure in the BFWP system and propose recommendations to reduce the failure risk to the lowest possible level (insignificant risk). The research methodology begins with a backflow failure analysis, followed by a Fault Tree Analysis (FTA) to construct the logical failure structure, identify contributing events, and determine the Minimal Cut Sets (MCS) and the most dominant critical events. Once the critical events are identified, they are further analyzed using the Five Whys method, progressing from the highest- to the lowest-priority critical events. The results show that the ARC Valve and the check valve are the most critical components, with a Structural Importance Degree (SID) value of 0.7369, followed by the pump components with a value of 0.2344. The reliability of the ARC Valve is highly dependent on the performance of its internal functions, namely the check valve, modulation, flow sensing, and pressure reduction mechanisms. Failure of any of these functions can lead to malfunction of the ARC Valve. Meanwhile, pump failures are also analyzed because pump operating fluctuations significantly affect ARC Valve performance, as the ARC Valve is a pilot-operated valve whose actuation depends on the working fluid. Pump failure is caused by a reduction in hydraulic power resulting from decreased pressure, reduced flow capacity, or complete loss of discharge. It may also result from a complete loss of hydraulic power due to system trips or scheduled maintenance activities. Based on the analysis, an internal inspection program for the ARC Valve every two years is recommended, along with the addition of protection layers through system redesign to control the risks of backflow and reverse rotation, thereby improving the operational reliability of the BFWP. The addition of two protection layers, namely a surge tank and a one-way clutch, can reduce the probability of failure to 10⁻⁶ per year, which falls within the insignificant risk category.
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