Atmospheric corrosion kinetics and dynamics of Karachi onshore areas

Atmospheric corrosion kinetics and dynamics (rate and factors) of karachi coastal city was ascertained at a couple of locations in the vicinity of arabian seashore i.e. hawksbay and seaview township by complying iso 9223,astm g01 and astm g50 norms. both exposure test sites were located at west to south-westward wind corridor. data was collected for exposure of mild steel coupons at these two locations and their meteorological conditions were logged for a period from march 2005 to april 2007. chloride and sulfur dioxide were measured by employing iso 9225 standard. severe degree of material depletion for mild steel coupons was observed at both test locations. mass loss was higher at hawksbay test site than at sea view township. maximum mass loss was observed during monsoon period probably due to rainfall and strong sea wave action which produced enriched marine aerosols and boosted chloride deposition rates. although paucity of rainfall was observed but substantial relative humidity level was recorded during test period. comparison of the results indicated that corrosion rate was higher at hawksbay test site as compared to seaview test site. goethite and lepidocrocite were identified as major corrosion products by scanning electron microscopy while it was also revealed that major portion of lepidocrocite phase was transformed into goethite at seaview test site. as goethite phase is thermodynamically more stable and less vulnerable to further recurrence of corrosion as compared to lepidocrocite phase which may be attributed to less corrosion rate measured at seaview test site. since corrosion rate at both locations were gauged in the range of 65> rcorr ≤ 150 in terms of μm.year-1 so this study ranked the corrosivity of these two test locations as c5 i.e. very high marine corrosivity. © 2015,chemical society of pakistan. all rights reserved.