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The Weibull Time-Dependent Growth Model of Marine Corrosion in Seawater Ballast Tank

Norhazilan Md Noor, and Smith, Georgr H. , and Nordin Yahaya, (2007) The Weibull Time-Dependent Growth Model of Marine Corrosion in Seawater Ballast Tank. Malaysian Journal of Civil Engineering, 19 (2). pp. 142-155.

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Official URL: http://web.utm.my/ipasa/images/stories/MJCE/2007/vol_19_no_2/5Dr.%20Nor%20Hazilan.pdf

Affiliations

Universiti Teknologi Malaysia. Faculty of Civil Engineering
University of Exeter, UK, School of Geography, Archaeology and Earth Resources, Cornwall Campus, Penryn Cornwall TR10 9EZ, United Kingdom
Universiti Teknologi Malaysia. Faculty of Civil Engineering

Abstract

This paper demonstrates the application of the probability distributions in modelling the time-dependent growth behaviour of corrosion pits in vessel’s seawater ballast tanks. The proposed model is capable of projecting the likely growth pattern of corrosion pits in the future by eliminating the dependent factors governing to corrosion rate such as environmental factors, properties of material and operational condition. To express appropriately the high variability of corrosion wastage which contributes to the uncertainties in corrosion assessment, the Weibull probability distributions were proposed which are able to predict the growth of corrosion pit in seawater ballast tank. It is obvious that the provided information from the vessel inspections is full of uncertainties, owing to the nature of marine corrosion as reflected by the poor correlation result of averaged depth against time. In spite of the drawback, the research is able to demonstrate the optimisation of the data purposely for corrosion growth prediction. The predicted data as compared to actual data yields results with moderate accuracy based on Root-Mean-Square-Error (RMSE), yet still promising provided that better quality data can become available in the future. The proposed probabilistic models are intended to simplify the modelling process so that the available data can be fully utilised for prediction and structural evaluation purposes


Kertas kerja ini menunjukkan bagaimana aplikasi taburan kebarangkalian dalam pemodelan sifat pertumbuhan lubang pengaratan sebagai fungsi masa bagi struktur tangki ballast kapal laut. Model yang dicadangkan berkeupayaan meramal corak pertumbuhan yang sebenar di masa hadapan tanpa mengambil kira faktor kebergantungan yang pada kebiasaannya mempengaruhi kadar pertumbuhan karat seperti faktor persekitaran, sifat bahan binaan dan juga faktor operasi. Untuk menggambarkan secara tepat serakan dimensi pengaratan yang tinggi yang sering menyebabkan ketidakpastian dalam penilaian pengaratan, taburan kebarangkalian Weibull telah dicadangkan supaya ramalan kedalaman pengaratan di dalam tangki ballast kapal laut di masa hadapan dapat dijalankan. Kajian jelas menunjukkan data pengaratan yang digunakan dipengaruhi oleh ketidakpastian disebabkan oleh faktor pengaratan marin itu sendiri seperti yang ditunjukkan oleh keputusan korelasi yang lemah di antara purata kedalaman lubang karat dan umur kapal. Di sebalik masalah yang dinyatakan, kajian ini masih mampu menunjukkan bagaimana penggunaan data pengaratan dapat dioptimakan bagi tujuan penilaian keutuhan struktur. Keputusan perbandingan di antara data sebenar dan data ramalan telah menunjukkan keputusan dengan ketepatan yang sederhana berdasarkan nilai ralat yang dikira menggunakan kaedah Root-Mean-Square-Error (RMSE) tetapi berpotensi jika lebih banyak data berkualiti dapat diperolehi. Model yang dicadangkan bertujuan untuk memudahkan proses pemodelan agar data yang diperolehi dapat digunakan sepenuhnya bagi tujuan ramalan dan penilaian keutuhan struktur.

Item Type:Journal
Additional Information:The author would like to express deep gratitude to MOSTI, MOHE and UTM for providing with fund and facilities to conduct the research.
Keywords:Corrosion; Weibull Probability; Ballast Tank Karat; Weibull; Tangki Ballast; Kebarangkalian
Subjects:T Technology, Engineering
ID Code:5298

Melchers R.E. (1999) Corrosion Modelling for Steel Structures, Journal of Constructional Steel Research, 52 : 3-19.

Noor, M.N. (2007) A Generic Assessment Approach to the Analysis of Corrosion Data and its Application on Structure Reliability, PhD Thesis, Heriot-Watt University, Edinburgh.

Paik J.K. (2004) Corrosion Analysis of Seawater Ballast Tank Structures, International Journal of Maritime Engineering, 146 Part A1 : 1-12.

Paik J.K. and Thayamballi A.K. (2002) Ultimate Strength of Ageing Ships, Journal Engineering for the Maritime Environment, 216 : 57-77.

Paik J.K, Thayambali A.K., Park Y.I. (2004) A Time-dependent Corrosion Wastage Model for Seawater Ballast Tank Structures of Ships, Corrosion Science, 46 (2) : 471-486.

Wang G., Spencer J., Elsayed T. (2003) Estimation of Corrosion Rates of Structural Members in Oil Tankers, Proceedings of OMAE 2003, 22nd International Conference on Offshore Mechanics and Arctic Engineering, Cancun, Mexico.

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