Abstract

Microbial corrosion of stainless, mild and carbon steel coupons in a semi static freshwater habitat was carried out monthly for a period of one year. Corrosion rate was determined by weight loss. Carbon steel had corrosion rate of 44 g/year, mild steel 27 g/year, stainless steel 0.64 g/year. Ecological quality parameters of the river water for rainy season decreased from April to October, respectively in the following trend; total dissolved solids (23 to 2.31) mg/l, total suspended solids (40 to 12) mg/l, total organic carbon (78.24 to 4.33) mg/l, conductivity (43 to 4.73) µs/cm, salinity (31 to 3.10) mg/l, oil and grease (34.23 to 1.67) mg/l, Chloride (52.11 to 1.05) mg/l, Sulphate (33.14 to 1.15) mg/l, Sulphite (8.11 to 10.14) mg/l, pH(6.4 to 6.0), temperature (27 to 25°C), biochemical oxygen demand (64.13 to 1.34) mg/l. That of dry season (November to March) respectively showed this trend. Total dissolved solids (3.14 to 52.11) mg/l, total suspended solids (9 to 40) mg/l, total organic carbon (5.10 to 10.24) mg/l, conductivity (6.29 to 104) µs/cm, salinity (5.11 to 87.33) mg/l, oil and grease (2.14 to 1.82) mg/l, Chloride (1.02 to 2.11) mg/l, Sulphate (0.17 to 4.95) mg/l, Sulphite (11.10 to 16.23) mg/l, pH (6.1 to 6.0), Temperature (25 to 26°C), biochemical oxygen demand (1.53 to 7.31) mg/l. Weight loss of stainless, mild and carbon steel for rainy season (April to October) respectively, and showed the following trend (0 to 0.030), (0.695 to 1.568), and (1.000 to 2.316) g, while the dry season (November to March) respectively showed the following trend (0.044 to 0.111), (1.586 to 5.771) and (2.325 to 9.131) g. Corrosion rate of stainless, mild and carbon steel for rainy season (April to October) respectively showed the following trend (0 to 0.004), (0.695 to 0.244) and (1.000 to 0.331) g/month while the dry season (November to March) showed the following trend respectively (0.006 to 0.009), (0.198 to 0.481), and (0.291 to 0.761) g/month. The use of stainless steel, if not already in use should be encouraged as a material for pipelines, flowlines and bulklines in the Nigerian Petroleum industry. Integrity checks on these surface facilities should be increased in the dry season.

Key words: Freshwater, ecological quality parameters, corrosion rate, weight loss.