Atmospheric corrosion kinetics and dynamics of electrogalvanized mild steel in southeastern coastal area of China–Pakistan Economic Corridor

Abstract

This study aims to examine atmospheric corrosivity, corrodants, and corrosion products of southeastern coastal area of China–Pakistan Economic Corridor as per ISO protocols 9223 and 9225, and ASTM standards G1, G50, G140‐02, D4458‐94, and D2010. Test sites are located at National Institute of Oceanography (NIO) and Karachi Port Trust (KPT) at the banks of the Arabian Sea. Electrogalvanized mild steel test coupons were exposed, and levels of corrodants (sulfur dioxide, chloride, and time of wetness) were measured for a period of 24 months, from May 2014 to May 2016. Corrosivity category C5+ is established in terms of the corrosion rate for both NIO and KPT test stations, which does not coincide with the corrosivity category C5 ascertained by employing environmental characteristics and atmospheric corrodants. Corrosion kinetic parameter “n” and correlation coefficient (R2) are 0.71 and 0.97 for NIO and 0.96 and 0.97 for KPT, respectively. Scanning electron microscopy/energy‐dispersive spectroscopy, Fourier‐transform infrared spectroscopy, and X‐ray diffraction spectroscopy have corroborated the presence of simonkolleite and hydrozincite, zinc oxide, zinc hydroxychloride, and zinc in corrosion products at both test sites.

Physicochemical studies of galvanized steel corrosion in urban, industrial, and marine environments, and corrosion mapping of Karachi city: An important coastal city of the 21st‐century modern maritime silk route

“…The corrosion rate was calculated by using the mass loss measurements, with the following relation [ 25 ] : where C is the corrosion rate in μm/year, K c the constant, whose value is 87,600, [ 25 ] Δ W the mass loss in mg, A the area in cm 2 , D the density in g/cm 3 , and t the time of exposure in hours.…”

“…The corrosion rate was calculated by using the mass loss measurements, with the following relation [25] :…”

“…where C is the corrosion rate in μm/year, K c the constant, whose value is 87,600, [25] ΔW the mass loss in mg, A the area in cm 2 , D the density in g/cm 3 , and t the time of exposure in hours.…”

“…Previously, authors have explored the atmospheric corrosion of galvanized steel with a limited scope at two sites in the Karachi city. [ 24,25 ]…”

“…It is an important part of the ongoing China–Pakistan Economic Corridor (CPEC) project, which is integrated with the 21st‐century modern maritime silk route. [ 24,25 ] Besides being a coastal city, it has two main rivers, namely Lyari and Malir rivers, and many streams including Gujjar, Gogni, Thado, and Orangi that flow through Karachi and drain into the Arabian Sea. These rivers and streams carry untreated wastewater of both domestic and industrial origin.…”