Investigations on Atmospheric Corrosion of Mild Steel in
Mauritius through Mass Loss and 2 D Surface Analysis
Paper Presenter and Author: B. Yashwansingh R. Surnam, PhD Scholar at
UoM
Losses due to corrosion have been found to make a significant impact on
the economy of many countries. Worldwide, studies have shown that the
overall cost of corrosion amounts to at least 4-5% of the gross national
product, and the major contributor to this cost is atmospheric corrosion.
In India, in 2004 for example, corrosion damage was estimated to be
responsible for losses to the national economy amounting to around
approximately £ 2.5 billion per year. Therefore, determining the
corrosivity of the atmosphere in any country is essential as it would
enormously facilitate the task of selecting materials, protection systems,
maintenance intervals, and corrosion allowance for metallic structures
exposed outdoors. This would help the country in its sustainable
development through a better use of its resources.
In Mauritius also, atmospheric corrosion is a serious problem. Being a
tropical country, it consists of an atmosphere which promotes atmospheric
corrosion. Hence, with the increasing use of steel, especially low carbon
steel, in the fabrication of structures and construction of buildings,
modelling the corrosivity of the Mauritian atmosphere is essential.
In this context, a study was started in November 2006. Commercially
available mild steel samples were exposed outdoors at Reduit according to
BS 8565. The specimens, in sets of four, were removed after 3, 7, 12,and
19 months. They were cleaned according to BS 7545 and their mass loss
was determined. While cleaning the specimens, it was found that the
surface of the base metal consisted of a large number of pits, indicating
that the mild steel sample was corroding in a general non-uniform manner
rather than uniformly. In order to understand how the base metal
corrodes below the rust layer, a 2D surface roughness analysis was
performed using the Talysurf Series 2 profilometer.
From the mass loss values, it was found that the average corrosion rate of
the mild steel specimens for the first year of exposure is 347 gm-2/year.
According to ISO 9223, the site at Reduit falls in category C3 which refers
to one with medium corrosivity. It can therefore be expected that the
industrial and marine regions in Port Louis and the coastal regions near
the shorelines can have a higher corrosivity and therefore fall in the C4
category.
As for the 2D surface roughness analysis, amplitude and spacing
parameters, such as Rt and Rsm respectively, were studied. They
correlate well with the mass loss values. Qualitatively, they can be used to
explain the corrosion behaviour of the exposed specimens. Taking into
consideration previous studies performed in this field, the corrosion
process on the mild steel surface was modelled.
This study is, however, part of an ongoing research work. The results of
only one site is presented. Investigations are ongoing at four sites in
different regions on the island. The results from this study together with
those that would be obtained from other sites would be used to finally
formulate a generic model of corrosivity in Mauritius to help researchers,
designers, as well as practitioners .
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