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Eingeladener Vortrag
- nein (8)
Geothermieanlage werden teilweise unter extremen Bedingungen mit sehr salzhaltigen Wässern betrieben. Obwohl C-Stahl häufig für die Konstruktion verwendet wird, ist er in einem Hoch-temperatur- und Hochdrucksystem anfällig für gleichmäßige und örtliche Korrosion. Daher soll ein Beschichtungssystem den C-Stahl schützen.
Schlussverfolgung
Es ist notwendig, die optimale SiO2-Zugabe zur organischen Beschichtung zu untersuchen, damit deren Eigenschaften, wie z.B. Haftfestigkeit, optimale Schichtdicke, und
Temperaturbeständigkeit, verbessert werden.
Das derzeitige Projekt zielt auf die Zugabe von Polyanilin (PANi) als Wirkstoff zur Verbesserung der Schichteigenschaften für die Erhöhung der Korrosionsbeständigkeit des Systems in stark salzhaltigen Medien bei höheren Temperaturen.
Geothermal brine is considered to be an aggressive environment as it contains various dissolved salts. Even though carbon steel is commonly used as a construction material due to its machinability and economical reason, it is susceptible to uniform and localized corrosion in a high temperature and high pressure system. Therefore, a coating system is introduced to protect the carbon steel against corrosion in such environment.
-It is necessary to find the optimum composition of SiO2 addition in the organic coatings to enhance the material performance, i.e. coatings adhesion, thickness optimization, thermal resistance.
Current project aims at the addition of Polyaniline (PANi) as the active agent to improve the corrosion resistance of materials against a high saline medium at elevated temperatures.
Geothermal brine is considered to be an aggressive
environment as it contains various dissolved salts.
Even though carbon steel is commonly used as a
construction material due to its machinability and
economical reason, it is susceptible to uniform and
localized corrosion in a high temperature and high
pressure system. Therefore, a coating system is
introduced to protect the carbon steel against
corrosion in such environment.
1. Carbon steel is susceptible to uniform corrosion in presence of oxygen, with corrosion rate of immersion at 150 °C of 0.39 mm/a.
2. Exposure test of carbon steel at 150°C and 10 bar (pressurized by Ar) results in pitting corrosion with depth of 19 µm and width 4 µm on average.
3. OCP measurement shows that the stability of measurement is reached after 40 hours of immersion in the solution.
4. EIS measurement is useful to observe the effect of temperature, immersion time, and coating composition on the corrosion processes of coated metals for use in geothermal application.
Geothermal brine is a complex system containing a wide variety of dissolved salts resulting from the condition s in a geothermal well. These fluids lead to corrosion in pipes and other parts of geothermal system construction and necessitate intense research efforts in finding new suitable materials. Carbon steel is susceptible to corrosion in geothermal brine especially when it is exposed to a high temperature and high-pressure medium, which is considered to be an aggressive environment. An artificial geothermal water, bas ed on a brine composition found in Indonesia, was used to investigate the performance of high alloyed materials. The electrolyte has pH 4 and contains 1,500 mg/l Cl-, 20 mg/l SO4 2-, 15 mg/l HCO3 -, 200 mg/l Ca 2+, 250 mg/l K+, and 600 mg/l Na+. In order to protect the bare material in geothermal application, it is necessary to either use high alloyed material s or coatings. In this research, a coating system consisting of polyaniline and silicon dioxide was investigated regarding its behavior to protect carbon steel. In detail, the effect of SiO2 and polyaniline (PANi) addition was evaluated by exposure and electrochemical tests for 7 days, i.e. electrochemical impedance spectroscopy (EIS) and open circuit potential (OCP ) at room temperature and 150 °C with 1 MPa pressure .
Electrochemical study of polyaniline/silicon dioxide containing coatings in geothermal solution
(2018)
Polyaniline/Silicon Dioxide containing coatings were electrochemically investigated in a saline geothermal solution.
With the increase of exposure time, impedance values of coated specimens decreased at low frequency, which could be caused by the decrease of pore resistance due to electrolyte or water uptake.
Coating system needs further optimization work.
Geothermal brine is a complex system containing a wide variety of dissolved salts resulting from the condition s in a geothermal well. These fluids lead to corrosion in pipes and other parts of geothermal system construction and necessitate intense research efforts in finding new suitable materials. Carbon steel is susceptible to corrosion in geothermal brine especially when it is exposed to a high temperature and high-pressure medium, which is considered to be an aggressive environment. An artificial geothermal water, bas ed on a brine composition found in Indonesia, was used to investigate the performance of high alloyed materials. The electrolyte has pH 4 and contains 1,500 mg/l Cl-, 20 mg/l SO4 2-, 15 mg/l HCO3 -, 200 mg/l Ca 2+, 250 mg/l K+, and 600 mg/l Na+. In order to protect the bare material in geothermal application, it is necessary to either use high alloyed material s or coatings. In this research, a coating system consisting of polyaniline and silicon dioxide was investigated regarding its behavior to protect carbon steel. In detail, the effect of SiO2 and polyaniline (PANi) addition was evaluated by exposure and electrochemical tests for 7 days, i.e. electrochemical impedance spectroscopy (EIS) and open circuit potential (OCP) at room temperature and 150 °C with 1 MPa pressure.
Electrochemical deposition of polyaniline on carbon steel for corrosion study in geothermal solution
(2018)
Polyaniline has been widely developed for many applications, e.g., sensor, supercapacitor component, electrochromic devices, and anticorrosion pigments [1]. Although the addition of polyaniline pigment in organic coatings has been an alternative for corrosion protection in industrial application, the protection mechanism is still not fully understood [2]. Herein in this study, as a part of the development of polyaniline/silicon dioxide coating for geothermal application, polyaniline has been deposited electrochemically on carbon steel surface and tested in geothermal solution to study the contribution of polyaniline in the corrosion protection of a polyaniline-based composite in the geothermal system. The electrochemical deposition was carried out by immersing carbon steel in 0.1 M oxalic acid and 0.05 M aniline, with the polarization potential of -0.6 – 1.5 V vs. Ag/AgCl, and a scan rate of 10 mV/s. To observe the surface/interface reaction between the electrolyte and electrode surface during the electrochemical polymerization, electrochemical impedance spectroscopy (EIS) measurement was applied after each cycle. For corrosion study in the geothermal application, this experiment used an artificial geothermal solution with the composition of 1,500 mg/l Cl-, 20 mg/l SO42-, 15 mg/l HCO3-, 200 mg/l Ca2+, 250 mg/l K+, and 600 mg/l Na+, and pH 4 to simulate a geothermal brine found in Sibayak, Indonesia. Electrochemical measurements were performed by monitoring the open circuit potential over seven days, with the interruption of EIS every 22 hours. The experiments were performed at room temperature and 150 °C (1 MPa) in a free oxygen environment. Polyaniline coated carbon steel is more durable in a room temperature environment compared to 150 °C, which could be caused by the iron oxalate dissolution at elevated temperature. This degradation was further proven by the impedance spectra, which showed a reduction of approximately ten times for specimens measured at 150 °C as compared to the specimens measured at room temperature.
According to the results of the experiments carried out, the following points can be concluded:
1. Exposure tests showed that specimens with the addition of SiO2 particles and polyaniline particles exhibit better corrosion resistance than specimens with the addition of only polyaniline particles or binder only.
2. Open circuit potential measurements showed that in the beginning of the experiments, both coatings had an open circuit potential 100 mV higher than carbon steel. Within one day of immersion, the potential of carbon steel increased significantly, indicating the formation of oxide layer. After extended exposure the carbon steel potential sat between PS1 (which had higher potential) and PS2 (which had a lower potential) and all three were in the range –600 mV to –500 mV vs Ag/AgCl.
3. Both coatings PS-1 and PS-2 were degraded with increasing exposure time, shown by the decrease of absolute impedance value at low frequency range after 2, 4, and 6 days exposure.
4. Potentiodynamic test was performed after 3 hours and 6 days exposure, and it was shown that the coating in the initial stage exhibited more passive behavior than the specimens exposed for 6 days.