Synergetic effect of sulphur and nitrogen oxides on corrosion of galvanized roofing sheets in Ibeno and Ebocha (Niger delta, Nigeria)

Abstract

The synergetic effect of nitrogen dioxide (NO₂) and sulphur dioxide (SO₂) on corrosion of galvanized iron roofing sheets has been investigated. The field studies were conducted in Ibeno and Ebocha (Niger Delta, Nigeria). Specimens of the roofing sheets were exposed for one year to outdoor environment to record the mass loss. For each of the 12 monitoring stations, 6 rack assemblies of the samples were placed at intervals of 100 m (total distance of 600 m). The concentrations of the gases were measured with an automatic air pollution monitor. The mass loss and pollutants concentrations exhibited negative correlation with distance. The variables were subjected to regression analysis to determine the contribution of each of the individual gases and the combination of the gases on the pollution matrix. NO₂ showed significant influence on the corrosion, while SO₂ did not. The value of coefficient of determination of the combined effect of the two gases was greater than the individual effect of the highest correlated NO₂, while SO₂ exhibited lower value, suggesting that there was synergy between the two gases in the corrosion of the roofing sheets. The corrosion decreased with distance from gas flare points, implying that flaring should be reduced, possibly, by harnessing the exuded gas as fuel.