MICROBIOLOGICALLY INFLUENCED CORROSION OF CARBON STEEL IN AN AQUEOUS NATURAL GAS PLANT

In the aqueous natural gas plants, the injection well was corroded because of sulfuric acid addition to adjust pH for iodine separation. Microbial communities and corrosion in the plants were compared using sulfuric acid or hydrochloric acid as a pH conditioner. Genus Pseudomonas and methanogenic archaea were dominant in 16S rRNA gene library constructed from production water. The dominant SRB species was different depending on the pH conditioner. According to DAPI staining and DGGE analysis, the cell concentration increased and bacterial community changed. It was assumed that this phenomenon occurred due to contamination by microorganisms from the surrounding environment. The three month corrosion study showed that the general corrosion rate of carbon steel coupons in the injection tank using sulfuric acid as a pH conditioner was four times higher and the biofilm weight was one and a half times bigger than the injection tank using hydrochloric acid. One possible reason is that hydrogen sulfide produced by SRB corroded carbon steel. However, the pitting corrosion rate was the highest in the receiving tank which used no acid. This result indicated that of metal surface corrosion is caused a mechanism which includes an oxygen concentration cell formed by the heterogeneously-attached biofilm.