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Atmospheric Corrosion of Carbon Steel in Mauritius

Atmospheric Corrosion of Carbon Steel in Mauritius. B.Y.R. Surnam 1 , Prof. Chetty V. Oleti 2 1 Phd Scholar at University of Mauritius, Faculty of Engineering, Mechanical and Production Engineering Dept. 2 Project Supervisor. Outline of presentation. Introduction Methodology Results

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Atmospheric Corrosion of Carbon Steel in Mauritius

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  1. Atmospheric Corrosion of Carbon Steel in Mauritius B.Y.R. Surnam1, Prof. Chetty V. Oleti2 1Phd Scholar at University of Mauritius, Faculty of Engineering, Mechanical and Production Engineering Dept. 2Project Supervisor

  2. Outline of presentation • Introduction • Methodology • Results • Analysis of results and conclusion

  3. MAURITIUS • Introduction • Has a high humidity level. • Has substantial rainfall. • Is small and surrounded • by sea. Tropical country Expected high corrosion rate

  4. The aims of this study are: • To determine the corrrosivity of the Mauritius atmosphere through mass loss analysis. • To determine how the atmospheric corrosion of low carbon steel proceeds through surface roughness analysis. • To develop models for atmospheric corrosion in Mauritius.

  5. Methodology • Material used: low carbon steel, medium carbon steel • Size: 150 mm100 mm3mm • Sites: • Low carbon steel: Reduit, P.Louis, St Julien, Belle Mare • Medium carbon steel: Reduit, Vacoas, Palmar • Specimens exposed over a time period of 1 ½ years.

  6. At specific time intervals, they were removed and cleaned according to BS 7545 • Mass loss and average corrosion rate determined. • Cleaned specimens have rough surfaces which varies with time of exposure. • Cleaned specimens were selected and 2D and 3D surface roughness measurements were taken using Form TalySurf Series 2.

  7. Preparation of samples for exposure Selection of sites Exposure of samples Removal of samples after specific time intervals • Gathering of data for: • Atmospheric parameters • Pollution level • Level of airborne salinity Mass loss & corrosion rate determination through weight loss analysis and electrochemical tests respectively Analysis of surface texture to understand corrosion process Models to determine and predict corrosion loss in Mauritius

  8. Results • Mass loss

  9. Surface roughness

  10. Analysis and conclusion • According to ISO 9223 (1992), the sites at Belle Mare, St Juliend’Hotman and Reduit fall in category C 3,whereas the site at Port Louis falls in category C 4.

  11. 1st removal- Uneven general corrosion due to the presence of very porous rust layer on the metal surface 2nd removal- Rust layer starts to become protective and corrosion proceeds through pores producing pits. 3rd removal- The pits continue to grow in size as corrosion proceeds through pores. 4th removal – The pits grow in size but the metal at the top of the peaks are also consumed. So, they become shallower but larger. Description of the corrosion process taking the roughness parameters into consideration.

  12. Modelling of atmospheric corrosion degradation results of mass loss • Dependent variable (DV): Corrosion loss (obtained from mass loss) • Independent variables (IVs): • Time of exposure (days) for each set of samples removed at each removal. • The average daily values of the following atmospheric parameters corresponding to the exposure period of the samples: • Relative humidity; • Rainfall; • Hours of sunshine; • Wind speed; • Temperature; • 24 hours average concentration of sulphur dioxide in the atmosphere. • The yearly average deposition rate of air borne salinity. • The carbon content of the carbon steel.

  13. Model: • ln (Depth of corrosion) = -1.223 -2.262(Carbon Content) + 0.067(Daily amount of sunshine) + 0.620 [ln (Days of exposure)] • R value = 0.93

  14. Other models • Electrochemical tests for only one site (St Julien): where C- corrosion loss (um/yr), t- time in hrs • From surface roughness tests

  15. To conclude: • 3 models have been developed to predict atmospheric corrosion. • The corrosivity of the atmosphere, according to ISO 9223 (1992) and taking low carbon steel into consideration, in Mauritius was finally described as falling in: • Category C 4 for Port Louis. • Category C 3 for all the regions in the island apart from Port Louis.

  16. Atmospheric corrosion proceeds when the rust layer is wet and decreases drastically, behaving like a protective coating, when it is dry. • The corrosion rate is very high initially (first 3 months) due to the unprotective, porous and thin rust layer. With time, it grows into a protective one and the corrosion rate decreases. Still, the carbon steel continues to corrode appreciably due to cracks formed in the rust layer such that the corrosion loss can be represented by the bilogarithmic equation. • The atmospheric corrosion attack and the development of the pores and cracks in the rust layer is a random process.

  17. Thank you

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