Abstract
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.
Highlights
U procesu eksploatacije nafte, zbog prisustva soli i rastvorenih gasova ugljen-dioksida i vodonik-sulfida, korozija intenzivno napada postrojenja za eksploataciju i transport fluida: sirove nafte, gasa i vode
Ovaj model je razvijen na bazi velikog broja laboratorijskih rezultata i veliku pažnju poklanja uticaju zaštitnog sloja na čeliku na povišenim temperaturama, sve do 150 °C
Spoljašnjeg prečnika 168,27 mm (Severnoamerički standard NPS 6 – Nominal Pipe Size 6′′, ili metrički DN – Diameter Nominal 150 mm) izgrađeni su od ugljeničnog čelika API 5L X52 sa dodatkom za koroziju od 3 mm u debljini zida cevi
Summary
U procesu eksploatacije nafte, zbog prisustva soli i rastvorenih gasova ugljen-dioksida i vodonik-sulfida, korozija intenzivno napada postrojenja za eksploataciju i transport fluida: sirove nafte, gasa i vode. Pritisak nafte u ležištu opada sve dok se ne izjednači sa pritiskom u bušotini i tada se eksploatacija nafte najčešće obavlja korišćenjem potapajućih pumpi. U pogledu izbora materijala cevovoda i potrebnog dodatka u debljini zida cevi zbog zaštite od korozije, dva osnovna pristupa u praksi su modelovanje korozije i procena efikasnosti primenjenih korozionih inhibitora. Danas postoji veliki broj modela korozije koji su poznati pod svojim komercijalnim nazivima, jer su razvijani kao kompjuterski programi. Sve velike naftne kompanije razvile su sopstvene programe za praćenje korozije cevovoda od ugljeničnih čelika za transport fluida na bazi primene postojećih, ali i sopstvenih modela korozije. Ovaj model je razvijen na bazi velikog broja laboratorijskih rezultata i veliku pažnju poklanja uticaju zaštitnog sloja na čeliku na povišenim temperaturama, sve do 150 °C. USL/ULL (University of Louisiana at Lafayette) [32,33,34,35] i Cormed (Elf) [36,37,38,39,40,41,42,43]
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