Study on Effects of Surface Roughness Variations on Corrosion Resistance of Metal Components

Duplex is the most commonly used stainless steels for offshore applications. It consists
of ferritic and austenitic lattice structures which deliver both strength and ductility. It
combines the basic toughness of the more common austenitic stainless steels with the
higher strength and improved corrosion resistance of ferritic steels.
Duplex has made most significant contribution to fight against corrosion offshore. These
have often been adopted on offshore structures in preference to carbon steel or other
stainless steels. The outer surface of offshore metal components is widely exposed to the
corrosion. Marine environment is the most aggressive environment for corrosion
activities to take place. The dominant factors of marine environment are considered by
extreme temperatures, humidity, and air contaminants.
The objective of this project is to study correlation between surface roughnesses of
metals with its corrosion resistance behavior. The methodology consists of preparation
of specimens, surface roughness measurement by using surface profiler, and corrosion
testing in the corrosion chamber by applying salt spray test ASTM B 117 standard
which is the most practical laboratory corrosion test to accelerate the corrodibility of the
metals.
The outcomes of the testing indicate duplex which has best surface finishing is not
affected by corrosion activities. Duplex with the surface roughness values less than
1.OOum have the best corrosion resistance and preferable compared to same metal which
have greater values of Ra. The lower the value of Ra, thus it may sustain failures of
corrosion in longer periods.