Atmospheric Corrosion of Atmospheric Corrosion of Carbon Steel in MauritiusCarbon Steel in Mauritius

B.Y.R. SurnamB.Y.R. Surnam11, Prof. Chetty V. Oleti, Prof. Chetty V. Oleti22

11Phd Scholar at University of Mauritius, Faculty of Phd Scholar at University of Mauritius, Faculty of Engineering, Mechanical and Production Engineering Engineering, Mechanical and Production Engineering Dept.Dept.

22Project SupervisorProject Supervisor

Outline of presentationOutline of presentation

• IntroductionIntroduction

• MethodologyMethodology

• ResultsResults

• Analysis of results and conclusionAnalysis of results and conclusion

• IntroductionIntroduction

MAURITIUS

Tropical country •Has a high humidity level.•Has substantial rainfall.•Is small and surrounded by sea.

Expected high corrosion rate

The aims of this study are:The aims of this study are:

• To determine the corrrosivity of the To determine the corrrosivity of the Mauritius atmosphere through mass Mauritius atmosphere through mass loss analysis.loss analysis.

• To determine how the atmospheric To determine how the atmospheric corrosion of low carbon steel proceeds corrosion of low carbon steel proceeds through surface roughness analysis.through surface roughness analysis.

• To develop models for atmospheric To develop models for atmospheric corrosion in Mauritius.corrosion in Mauritius.

MethodologyMethodology

• Material used: low carbon steel, medium carbon steelMaterial used: low carbon steel, medium carbon steel• Size: Size: 150 mm150 mm100 mm100 mm3mm 3mm • Sites: Sites:

– Low carbon steel: Reduit, P.Louis, St Julien, Belle MareLow carbon steel: Reduit, P.Louis, St Julien, Belle Mare– Medium carbon steel: Reduit, Vacoas, PalmarMedium carbon steel: Reduit, Vacoas, Palmar

• Specimens exposed over a time period of 1 ½ years.Specimens exposed over a time period of 1 ½ years.

• At specific time intervals, they were At specific time intervals, they were removed and cleaned according to removed and cleaned according to BS BS 75457545

• Mass loss and average corrosion rate Mass loss and average corrosion rate determined.determined.

• Cleaned specimens have rough surfaces Cleaned specimens have rough surfaces which varies with time of exposure.which varies with time of exposure.

• Cleaned specimens were selected and 2D Cleaned specimens were selected and 2D and 3D surface roughness measurements and 3D surface roughness measurements were taken using Form TalySurf Series 2.were taken using Form TalySurf Series 2.

Results Results • Mass lossMass loss

0

5

10

15

20

25

0 100 200 300 400 500 600 700

Days of exposure

Mas

s lo

ss (

g)

Palmar- study A Vacoas - study A Reduit - study APort Louis- study B StJulien d'Hotman- study B Belle Mare-study B

Reduit - study B

Surface roughnessSurface roughnessDays of exposure

Average Mass loss(g)

3D surface texture of samples exposed at Reduit, after

levelling and filtration78.9 3.023

391.9 11.203

Days of exposure: 78.9 Average Mass loss(g): 3.023

Days of exposure: 391.9 Average Mass loss(g):11.203

Analysis and conclusionAnalysis and conclusion

•   

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

Site Annual mass loss

(g)

Annual mass loss

(gm-2 /year)

Belle Mare 8.7 276

St Julien d’Hotman 11.1 352

Port Louis 13.4 425

Reduit 10.4 330

Description of the corrosion processDescription of the corrosion process taking the roughness taking the roughness parameters into consideration.parameters into consideration.

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.

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.

3rd removal-The pits continue to grow in size as corrosion proceeds through pores.

Modelling of atmospheric corrosion Modelling of atmospheric corrosion degradation results of mass lossdegradation results of mass loss

• Dependent variable (Dependent variable (DVDV): Corrosion loss (obtained from mass loss)): Corrosion loss (obtained from mass loss)

• Independent variables (IVs): Independent variables (IVs): – Time of exposure (days) for each set of samples removed at each Time of exposure (days) for each set of samples removed at each

removal.removal.– The average daily values of the following atmospheric parameters The average daily values of the following atmospheric parameters

corresponding to the exposure period of the samples:corresponding to the exposure period of the samples:• Relative humidity;Relative humidity;

• Rainfall;Rainfall;

• Hours of sunshine;Hours of sunshine;

• Wind speed;Wind speed;

• Temperature;Temperature;

– 24 hours average concentration of sulphur dioxide in the atmosphere.24 hours average concentration of sulphur dioxide in the atmosphere.– The yearly average deposition rate of air borne salinity.The yearly average deposition rate of air borne salinity.– The carbon content of the carbon steel.The carbon content of the carbon steel.

Model:Model:

• lnln (Depth of corrosion) = -1.223 -2.262(Carbon (Depth of corrosion) = -1.223 -2.262(Carbon Content) + 0.067(Daily amount of sunshine) + Content) + 0.067(Daily amount of sunshine) + 0.620 [0.620 [lnln (Days of exposure)] (Days of exposure)]

• R value = 0.93R value = 0.93

Other modelsOther models• Electrochemical tests for only one Electrochemical tests for only one

site (St Julien):site (St Julien):

where C- corrosion loss (um/yr), t- time in hrswhere C- corrosion loss (um/yr), t- time in hrs

• From surface roughness testsFrom surface roughness tests

To conclude:To conclude:• 3 models have been developed to predict 3 models have been developed to predict

atmospheric corrosion.atmospheric corrosion.

• The corrosivity of the atmosphere, The corrosivity of the atmosphere, according to ISO 9223 (1992) and taking according to ISO 9223 (1992) and taking low carbon steel into consideration, in low carbon steel into consideration, in Mauritius was finally described as falling Mauritius was finally described as falling in:in:– Category C 4 for Port Louis.Category C 4 for Port Louis.– Category C 3 for all the regions in the island Category C 3 for all the regions in the island

apart from Port Louis. apart from Port Louis.

• Atmospheric corrosion proceeds when the rust layer is wet Atmospheric corrosion proceeds when the rust layer is wet and decreases drastically, behaving like a protective and decreases drastically, behaving like a protective coating, when it is dry.coating, when it is dry.

• The corrosion rate is very high initially (first 3 months) due The corrosion rate is very high initially (first 3 months) due to the unprotective, porous and thin rust layer. With time, it to the unprotective, porous and thin rust layer. With time, it grows into a protective one and the corrosion rate grows into a protective one and the corrosion rate decreases. Still, the carbon steel continues to corrode decreases. Still, the carbon steel continues to corrode appreciably due to cracks formed in the rust layer such appreciably due to cracks formed in the rust layer such that the corrosion loss can be represented by the that the corrosion loss can be represented by the bilogarithmic equation.bilogarithmic equation.

• The atmospheric corrosion attack and the development of The atmospheric corrosion attack and the development of the pores and cracks in the rust layer is a random process.the pores and cracks in the rust layer is a random process.

Thank youThank you