Internal corrosion of carbon steel pipelines is a major problem encountered
in water service. In terms of prediction of the remaining lifetime for water
pipelines based on the corrosion allowance, the three main approaches are
corrosion modelling, corrosion inhibitor availability, and corrosion
monitoring. In this study we used two theoretical corrosion models, CASSANDRA
and NORSOK M-506 of quite different origin in order to predict uniform
corrosivity of hot aquifers in eight different pipelines. Because of the
varying calculation criteria for the different models, these can give very
different corrosion rate predictions for the same data input. This is
especially true under conditions where the formation of protective films may
occur, such as at elevated temperatures. The evaluation of models was
conducted by comparison using weight-loss coupons and three corrosion
inhibitors were obtained from commercial suppliers. The tests were performed
during the 60-day period. Even though inhibitors? efficiencies of 98% had
been achieved in laboratory testing, inhibitors? availabilities of 85% have
been used due to logistics problems and other issues. The results, given in
mmpy, i.e. millimeter per year, are very consistent with NORSOK M-506
prediction. This is presumably because the model considers the effect of the
formation of a passive iron carbonate film at temperatures above 80 ?C and
significant reduction in corrosion rate. Corrosion inhibitor A showed a
better performance than inhibitors B and C in all cases but the target
corrosion rates of less than 0.1 mmpy were achieved for all inhibitors. The
chemical type of corrosion inhibitor A is based on quaternary amines mixed
with methanol, isopropyl alcohol, xylene and ethylbenzene. Based on the
obtained results the carbon steel lifetime of 30 years, provided proper
inhibitors are present and 3mm corrosion allowance, can be achieved for hot
aquifers service with presented water compositions.
Internal corrosion of carbon steel piping in hot aquifers service
