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The screening of coatings shows that the modification by adding individual pigment was not sufficient to protect carbon steel even during a short-term exposure, indicated by the discoloration after only seven days of exposure.
Electrochemical tests indicated that the coating cathodically protects carbon steel or slows down the corrosion reaction.
A long-term exposure test confirmed that the PANI/SiO2 modified coating successfully protects the carbon steel in the Sibayak artificial geothermal water at 150 °C for 6 months.
Evaluation of corrosion resistance of metallic materials is essential to assure safe and reliable operation of geothermal sites. One need to be aware that corrosion is not a material's but a system property, determined by medium, material and construction aspects. Various corrosion types have to be evaluated. Conditions in laboratory shall reflect on-site reality. Depending on brine composition and temperature suitability of metallic materials can be ranked. Most important outcome of the research is that highly saline geothermal brines require high alloyed materials, for safe long-term operation.
Integrated Coating System for Corrosion Protection of Carbon Steel in Artificial Geothermal Brine
(2022)
Corrosive geothermal brines are a major challenge to geothermal power-plants. For cost reasons, plant designers prefer to use carbon and low alloyed steels, which are susceptible to uniform and localized corrosion when exposed to geothermal brines having acidic and saline properties. To solve such problem, coatings or inhibitors would be a protective solution as an alternative to the use of high alloyed materials.
This study investigated a coating system consisting of polyaniline/silicon dioxide based on resources locally available in Indonesia. Protection against corrosion of carbon steel was shown by long-term (28 day) exposure and electrochemical tests of coated carbon steels, performed in an artificial acidic and saline geothermal brine, comparable to the conditions encountered at a site in Indonesia.
Therefore, an integrated coating system is proposed for corrosion protection, combining the electrochemical functionality of polyaniline and the physical advantages of silica.
Influence of Precipitating Brine Components on Materials Selection for Geothermal Applications
(2021)
By exposure and electrochemical tests in the laboratory the Cu- and Pb-effect on corrosion behavior and performance of carbon steel and a corrosion resistant alloy could be assessed. Critical material specific properties were determined by static exposure and electrochemical tests in artificial geothermal water with high salinity and low pH, containing Cu/Pb.
It could be shown that significant Cu- resp. Pb-deposition and precipitation only occurred in combination with carbon steel. Corrosion resistant alloys (e. g. Cr- and Ni-dominated stainless steels) prevent the disturbing Cu-agglomeration resp. Pb-deposition. Therefore, they are suitable to be chosen for future design of geothermal piping system, either in massive or in cladded form. Regarding corrosion, formation of crevices with non-metallic materials shall be avoided.
So, in addition to its already known limited corrosion resistance, carbon steel shall not be used when copper or lead species are content of the geothermal brine. Otherwise precipitation and/or deposition of metallic copper resp. lead must be expected, increasing the susceptibility of clogging the piping system.
From the interactions and pitting corrosion point of view, corrosion resistant alloys (preferably Ni-rich) seem to be most favorable when selecting materials for applications in such geothermal brines.
Significant Cu-deposition and ‑precipitation only occurred in combination with carbon steel. High-alloyed materials prevent the disturbing Cu-agglomeration. Pb-deposition and ‑precipitation only occurred in combination with carbon steel. No negative Pb-effect could be observed in combination with high-alloyed steels. High alloyed corrosion resistant alloys are suitable and shall be chosen for future design of the piping system, either in massive or in cladded form, if formation of crevices with non-metallic materials can be excluded!
The electrochemical behavior of UNS N08031 was investigated as a function of electrode potential in Green-Death solution at 40 °C. The UNS N08031 surface is in a stable passive state during cyclic potentiodynamic polarization without an initiation and/or propagation of localized corrosion. In potentiostatic polarization of UNS N08031 for 3600 s, passive current density increases with an increase in the passivation potential from 0.7 to 1.0 VSSE (silver/silver chloride reference electrode in saturated potassium chloride) Electrochemical impedance spectroscopy (EIS) and Mott-Schottky (M-S) analysis showed that a more defective n-type semiconductive passive film forms as the potential increases. X-ray photoelectron spectroscopy (XPS) revealed that passive film consists of mainly chromium and minor iron and nickel oxides. The mechanism of the defective passive film formation is discussed. The increase of the applied potential is considered to be a reason for the change in passive film stability.
Since geothermal wells are a feasible energy source to replace fossil fuel supply, many technologies have been developed to take advantage of geothermal energy. Nevertheless, service conditions in geothermal facilities are in many cases extreme in terms of corrosion due to the chemical composition of hydrothermal fluids and temperatures. Therefore, materials selection based on preliminary material qualification is essential to guarantee a secure and reliable operation of the facilities. During operation of a geothermal research facility in Groß Schönebeck copper and lead effects have been found downhole. Occurring mechanisms and measures to prevent precipitation or scaling needed to be investigated as well as potential influences of such precipitates on corrosion resistance of metallic materials used for equipment.
This contribution deals with the evaluation of the corrosion behavior of carbon steel and corrosion resistant alloys in copper and/or lead containing artificial geothermal water, simulating the conditions in the Northern German Basin.
The behavior of these materials in an artificial geothermal water obtained by electrochemical measurements and exposure tests are presented. While carbon steel exhibits precipitation and deposition, higher alloyed material shows different response to such species and a higher resistance in saline geothermal water.
Basing on these results the suitability of the investigated corrosion resistant alloy is given for use in such conditions, whereas carbon steel creates difficulties due to its susceptibility to Cu- and Pb-precipitation.
The aim of the work presented was the evaluation of corrosion resistance
of various materials in geothermal Waters as a base to create a catalogue of suitable materials for applications in (not only) German geothermal power plants.
Users shall be enabled to have a basis for designing such facilities. High alloyed corrosion resistant alloys are suitable and do not cause copper or lead deposition. They shall be chosen for future design of the piping system, either in massive or in cladded form, if crevices formation with non-metallic materials can be prevented!
Biodiesel (FAME) from rapeseed is an environmentally friendly alternative to common fossil fuels. It is also suitable to serve as blending component to fuels like heating oil. If the fuel composition is changed, materials compatibility must be guaranteed. Adding polar biodiesel to nonpolar heating oil, changes the blend’s solvency and might cause swelling, extraction and solvation of polymers.
The objective of this research was to investigate the compatibility of polymeric materials, which are commonly used for components in middle distillate facilities, along with blends of heating oil and 20 % biodiesel (B20). For this propose, ACM, HNBR, FKM, PE, PA 6, POM, PUR and PVC were exposed to heating oil and B20 for 42 and 84 days at 40 °C. In addition, the polymers HNBR, FKM, PA, POM and PVC were also exposed at 70 °C. Furthermore, the resistance of polymers in eight-year aged B10 at 40 °C was evaluated. Ageing of biodiesel increases acidity which might propagate polymer corrosion.
The materials were evaluated as resistant, if the loss in tensile properties (tensile strength and elongation at break) and Shore hardness remained under 15 % compared to the initial unexposed material values. For investigations under compressed conditions, the compression set was determined for specimens of ACM, FKM and HNBR after exposure in heating oil B0 and B20 for 3,7,14, 28, 56 and 90 days at 40 °C according to ISO 815-1.
It was found that the resistance in B20 at 40 °C was given for all tested polymers except PUR. In the 8 years aged B10, PUR and POM were not compatible and ACM just conditionally compatible. At 70 °C, FKM and PVC were resistant in B20, whereas HNBR and PA 6 were not compatible. Swelling occurred for the elastomers ACM, HNBR and PUR.
“Corrosive to Metals” (H290) describes the general potential danger of a substance to metallic materials. Uniform and localized attack is considered. It has nothing to do with containment material. Corrosion resistance of materials is determined similarly, but with much lower threshold values.
Manual shall provide a simple test to easily determine the aggressivity potential to cause corrosion on metallic materials.
Even a simple test requires experienced personnel. There seems to be a need of awareness and understanding training for both officials and applicants.