51314-4031-Suitability of Alloyed Steels in Highly Acidic Geothermal Environments

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Product Number: 51314-4031-SG

ISBN: 4031 2014 CP

Author: Amela Keserovic

Publication Date: 2014

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With an estimated geothermal potential of 170 MW/year Lahendong geothermal field is one of the geothermal hotspots in Indonesia. Currently only 80 MW/year is being utilized but still enough to supply 60 % of North Sulawesi with electrical energy. One of the most promising wells on Lahendong geothermal field is the well LHD-23 due to its capacity of producing 35 MW/year of energy. However exploiting the geothermal fluid from that well represents a great challenge because of its extremely low pH that decreases down to 1.1 and high total dissolved solids of more than 3000 mg/L. As a result of such a corrosive environment and conditions the well experienced a breakdown in July 2011 due to the severe localized corrosion and it had to be shut down until its casing is recovered.This study helps to evaluate which of the materials present at the market could overcome the problem of corrosion and withstand such an aggressive environment. Therefore corrosion behaviour of three different steel grades (low-alloyed steel 25CrMo4 stainless steel X2CrNiMo17-12-2 and high-alloyed steel X1NiCrMoCu32 28-7) has been investigated in the synthetical geothermal brine (1500 mg/L chlorides 1600 mg/L sulphates pH 1.8) at 100 °C (1 bar) and 175 °C (8 bar) simulating the conditions present in the LHD-23 well at Lahendong geothermal field North Sulawesi Indonesia. The investigations were performed by means of electrochemical measurements and long term exposure tests in order to determine the critical potentials and corrosion rate.Preliminary results at 100 °C (1 bar) have shown low-alloyed steel 25CrMo4 actively corrodes in the investigated conditions with free corrosion potentials being in the range of critical values. Stainless steel X2CrNiMo17-12-2 and high-alloyed stainless steel X1NiCrMoCu32-28-7 have shown on contrary wide passive ranges and good repassivation behaviour. It is expected that with the temperature increase to 175 °C passive ranges of stainless steels would be reduced due to the shift of the critical potentials in cathodic direction. This hypothesis is currently being verified and the results will be presented on the NACE Corrosion 2014.Keywords: Lahendong geothermal steel corrosion electrochemistry