Abstract
Internal corrosion of pipelines occurs where water or other corrosive electrolyte accumulates. This is the basis for Internal Corrosion Direct Assessment (ICDA). Although ICDA focuses on nominally dry gas with episodes of water upset, the well accepted criteria for dry gas (e.g., water less than 112 mg/m3 or 7 pounds per million standard cubic feet, MMSCF) may be significantly influenced by the presence of bacterial biofilms and hygroscopic solids, such as iron oxide corrosion products and some salts. Therefore, understanding the changes in dew point induced by the presence of these compounds is necessary to better quantify gas quality requirements. The Multielectrode Array Sensor (MAS) probe was used to study the effect of biofilms and corrosion products on corrosion in high pressure gas mixtures. It was found that: (i) the MAS probe is sensitive in detecting localized corrosion in wet gas streams at pipeline pressures; (ii) the corrosion rate is sensitive to gas composition/quality; (iii) the presence of biofilm and corrosion products affected the dew point but the current water content specifications for gas are sufficiently conservative that this decrease in dew point is not a concern; and (iv) the corrosion under the biofilm once initiated at high humidity levels did not decrease even upon decrease of humidity to levels lower than needed to initiate corrosion.
