Sea water injection systems have traditionally been treated with biocide to inhibit growth of sulfate reducing bacteria (SRB) and reduce microbial induced corrosion (MIC). Laboratory experiments have shown that nitrate treatment can be an effective alternative to biocide treatment to reduce the number and activity of SRB. Based on such experiments the decision was made to implement nitrate treatment to the injection water on the oil platform Veslefrikk (North Sea). Addition of low dose of nitrate resulted in a decrease in the amount and activity of SRB in the water injection system. After 4 months nitrate addition, the activity of SRB in biofilm
samples were strongly reduced. Corresponding to the decrease in SRB, an enrichment of nitrate reducing bacteria (NRB) was observed. After 32 months nitrate treatment SRB numbers were reduced 20 000 fold and SRB activity 50 fold. Corrosion measurements on metal coupons
showed a decrease in weight loss from 0.7 mm/year to 0.2 mm/year. The results show that nitrate treatment can efficiently inhibit growth of SRB and control MIC in C-steel top side sea water injection systems. As opposed to the use of biocides such as glutaraldehyde, nitrate does not represent health hazard to platform personnel. Glutaraldehyde is classified as "Toxic" and may cause allergy to personnel handling the chemical. Inorganic nitrate salts have no negative environmental
implications.