Studi Numerik Pengaruh Notch terhadap Kegagalan Poros Pompa MCWP

fattahuddian, muhammad firda (2026) Studi Numerik Pengaruh Notch terhadap Kegagalan Poros Pompa MCWP. Masters thesis, Institut Teknologi Sepuluh Nopember.

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Abstract

Poros Main Cooling Water Pump (MCWP) Unit 3 PLTP Gunung Salak mengalami kegagalan fatigue pada September 2022, setelah 720 hari beroperasi pascaoverhaul 2020, dengan takikan gerinda pada permukaan poros teridentifikasi sebagai kandidat pemicu kegagalan. Metode. Penelitian ini bertujuan (1) menentukan radius takikan ekivalen dan faktor konsentrasi tegangan (Kts) berdasarkan Chart Peterson serta radius ekivalen yang merepresentasikan durasi kegagalan aktual melalui back-calculation Palmgren-Miner, dan (2) menentukan deviasi Kt dan faktor fatigue (Kf) antara Chart Peterson dan FEA pada berbagai radius perbaikan. Untuk tujuan pertama, radius takikan baseline (r = 0,735 mm) dianalisis melalui akumulasi kerusakan Palmgren-Miner terhadap seluruh fase pembebanan operasional (startup, operasi stabil, shutdown/trip), kemudian radius ekivalen yang merepresentasikan durasi kegagalan aktual (720 hari) ditentukan melalui back-calculation dengan dua model ekstrapolasi independen pendekatan ekstrapolasi dan power-law sebagai validasi silang. Untuk tujuan kedua, disimulasikan enam model geometri berbeda menggunakan Finite Element Analysis (ANSYS Mechanical 2025 R2): satu model baseline (r = 0,735 mm) dan lima model radius perbaikan (r = 4, 6, 8, 10, dan 11 mm), masing-masing dibandingkan terhadap prediksi Chart Peterson pada radius yang sama untuk menentukan pola deviasi Kt dan Kf, serta mengevaluasi pengaruh geometri partial arc perubahan sudut busur transisi akibat keterbatasan kedalaman penghilangan material (maksimal 3 mm, untuk mempertahankan dimensi poros) terhadap pola tersebut. Hasil. Radius takikan baseline (r = 0,735 mm; r/d = 0,005) menghasilkan Kts = 3,98 dan D_total = 0,6338 pada 720 hari, mendekati namun belum mencapai ambang kegagalan (D = 1). Back-calculation menentukan radius ekivalen sebesar r ≈ 0,634–0,655 mm hanya 0,1 mm ≈14% lebih tajam dari baseline. Deviasi Kf antara Peterson dan FEA pada kelima model radius perbaikan membentuk pola-U: −32,8% pada baseline, mengecil ke minimum −13,2% pada r = 6 mm, membesar kembali hingga −30,1% pada r = 11 mm dengan fraksi busur menurun dari 100% menjadi 48,1% seiring radius membesar, konsisten arah dengan studi validasi Kt sejenis (Sivák dkk., 2023). Penelitian ini berkontribusi berupa back-calculation sensitivitas radius takikan terhadap umur fatigue serta karakterisasi kuantitatif pengaruh partial arc terhadap validitas Kt analitik pada perbaikan radius.
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The Main Cooling Water Pump (MCWP) Unit 3 shaft at the Gunung Salak Geothermal Power Plant experienced a fatigue failure in September 2022 after 720 days of operation following a 2020 overhaul, with a grinding notch identified as a potential failure initiator. This study aims to (1) determine the equivalent notch radius and stress concentration factor (Kts) based on the Peterson Chart, as well as the equivalent radius representing the actual failure duration through Palmgren–Miner back-calculation, and (2) evaluate the deviations of the stress concentration factor (Kt) and fatigue stress concentration factor (Kf) between the Peterson Chart and Finite Element Analysis (FEA) for various repair radii. To achieve the first objective, the baseline notch radius (r = 0.735 mm) was analyzed using Palmgren–Miner cumulative damage across all operational loading phases, including startup, steady operation, and shutdown/trip. The equivalent radius corresponding to the observed 720-day failure duration was then determined through back-calculation using two independent extrapolation models, namely the Neuber-type and power-law models, for cross-validation. For the second objective, six geometric models were simulated using Finite Element Analysis in ANSYS Mechanical 2025 R2, consisting of one baseline model (r = 0.735 mm) and five repair-radius models (r = 4, 6, 8, 10, and 11 mm). Each model was compared with the corresponding Peterson Chart prediction to determine the Kt and Kf deviation patterns and to evaluate the influence of partial-arc geometry, specifically the change in transition-arc angle caused by the limited material-removal depth (maximum 3 mm to preserve shaft dimensions), on these deviations. The baseline notch radius (r = 0.735 mm; r/d = 0.005) produced a Kts value of 3.98 and a cumulative damage value (D_total) of 0.6338 after 720 days, approaching but not reaching the fatigue failure threshold (D = 1). The back-calculation estimated an equivalent notch radius of approximately 0.634–0.655 mm, representing a notch only about 14% sharper than the baseline. The Kf deviation between the Peterson Chart and FEA across the five repair-radius models exhibited a U-shaped trend, ranging from −32.8% at the baseline radius, decreasing to a minimum deviation of −13.2% at r = 6 mm, and increasing again to −30.1% at r = 11 mm, while the arc fraction decreased from 100% to 48.1% as the repair radius increased. This trend is consistent with the findings of a similar Kt validation study by Sivák et al. (2023). Overall, this study contributes a back-calculation method for evaluating notch-radius sensitivity to fatigue life and provides a quantitative characterization of the influence of partial-arc geometry on the validity of analytical Kt predictions in shaft radius repair.

Item Type:	Thesis (Masters)
Uncontrolled Keywords:	konsentrasi tegangan, takikan, busur parsial, fatigue, Finite Element Analysis, Palmgren-Miner, poros pompa stress concentration, notch, partial arc, fatigue, Finite Element Analysis, Palmgren-Miner, pump shaft
Subjects:	T Technology > TJ Mechanical engineering and machinery > TJ174 Maintenance and repair of machinery
Divisions:	Faculty of Industrial Technology and Systems Engineering (INDSYS) > Mechanical Engineering > 21101-(S2) Master Thesis
Depositing User:	Muhammad Firda Fattahuddian
Date Deposited:	05 Aug 2026 01:29
Last Modified:	05 Aug 2026 01:29
URI:	http://repository.its.ac.id/id/eprint/143729

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