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- Ipek, Nulifer, et al.
(author)
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Electrolytic pickling of duplex stainless steel
- 2005
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In: Materials and corrosion - Werkstoffe und Korrosion. - : Wiley. - 0947-5117 .- 1521-4176. ; 56:8, s. 521-532
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Journal article (peer-reviewed)abstract
- Pickling of duplex stainless steels has proved to be much more difficult than that of standard austenitic grades. Electrolytic pre-pickling is shown to be a key process towards facilitating the pickling process for material annealed both in the production-line and in laboratory experiments. The mechanism for the neutral electrolytic process on duplex 2205 and austenitic 316 steels has been examined and the oxide scale found to become thinner as a function of electrolytic pickling time. Spallation or peeling of the oxide induced by gas evolution did not play a decisive role. A maximum of about 20% of the current supplied to the oxidised steel surface goes to dissolution reactions whereas about 80% of the current was consumed in oxygen gas production. This makes the current utilisation very poor, particularly against the background of reports that in indirect electrolytic pickling only about 30% of the total current, supplied to the process, actually goes into the strip. A parametric study was therefore carried out to determine whether adjustment of process variables could improve the current utilisation.
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| 3. |
- Ipek, Nulifer, et al.
(author)
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Improvement of the electrolytic metal pickling process by inter-electrode insulation
- 2005
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In: Ironmaking & steelmaking. - 0301-9233 .- 1743-2812. ; 32:1, s. 87-96
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Journal article (peer-reviewed)abstract
- The existing industrial electrolytic steel pickling process is only 30% current efficient. Use of approximate modelling of the process and solution of the model predicts that inter-electrode insulation improves the current and energy efficiency, and this paper describes the experimental work that has validated this prediction. Some of the main results are: (a) the current efficiency varied from 20% without insulation to 100% with complete insulation, (b) the use of just partial insulations yielded a significant improvement in the process efficiency and at the same time maintained good electrolyte mixing and homogeneity which can not be attained with complete insulation. The theoretical foundations of this method and its various consequences are discussed. The method is relatively easy to apply to existing industrial electrolytic pickling tanks, and also provides system control flexibility for optimal pickling of different steel grades. The method's application cost is relatively low and saves investment in new equipment if a retrofit of an existing system is desired.
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| 5. |
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| 6. |
- Ipek, Nulifer, et al.
(author)
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Numerical and experimental study of the effect of gas evolution in electrolytic pickling
- 2006
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In: Journal of Applied Electrochemistry. - : Springer Science and Business Media LLC. - 0021-891X .- 1572-8838. ; 36:12, s. 1367-1379
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Journal article (peer-reviewed)abstract
- As part of a progressive approach to model the electrolytic pickling process, this paper focuses on the important aspect of hydrogen and oxygen gas evolution on the electrodes and on the steel strip being pickled. The system considered consists of type 316 stainless steel pickled in aqueous sodium sulphate, with lead anodes and stainless steel cathodes. The mathematical model is two-dimensional steady-state, and includes the differential equations describing the effect of migration, giving the potential and current fields, and the Tafel kinetic rate expressions for hydrogen and oxygen gas generation. Experiments were conducted to obtain a better understanding of the process and for model validation. Good agreement between the experimental measurements of the global current efficiency and the model predictions was obtained.
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| 7. |
- Ipek, Nulifer, et al.
(author)
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Simple analytical model predicting some features of the electrolytic steel-pickling process
- 2002
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In: Russian journal of electrochemistry. - 1023-1935 .- 1608-3342. ; 38:3, s. 238-246
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Journal article (peer-reviewed)abstract
- Electrolytic pickling of steel with neutral solutions, to remove the surface scale, reduces the need for the use of strong acids as needed in conventional pickling. This study is a step towards a more in-depth understanding of the factors affecting the former process. A theoretical model, sufficiently simplified to allow analytical solution, is developed and evaluated to provide a first approximation of the potential and current distributions in the electrolyte and steel band. To gain knowledge and validate the model, a small electrolytic pickling cell is constructed, and experiments, including bubble generation and motion observation, are conducted. The experimental work has shown the remarkable bubble production and adherence to the surfaces, and its effects on reducing pickling efficiency and uniformity. The pickling efficiency is about 30%, confirming other researchers' results. The analytical model shows trends very similar to those observed in the experiments, and provides very valuable guidance. It shows, for example, that the current efficiency decreases as the electrode-band distance increases, and it increases with the band thickness and the band-to-electrolyte conductivity ratio, The energy efficiency decreases by orders of magnitude faster than the current efficiency with all of the above-mentioned parameters, because of the correspondingly strong drop in the band-surface potential. A large amount of current is lost due to interelectrode short circuiting.
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| 9. |
- Skoglund, Peter, et al.
(author)
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Thermo-mechanical fatigue of grey cast iron for cylinder heads - Effect of niobium, molybdenum and solidification time
- 2018
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In: Materials Science Forum. - : Trans Tech Publications. - 0255-5476 .- 1662-9752. - 9783035710557 ; 925, s. 377-384
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Journal article (peer-reviewed)abstract
- Grey iron alloyed with molybdenum and niobium in seven different compositions has been casted using three, in industrial components viable, solidification times which resulted in 21 different samples. The samples have been investigated with respect to microstructure, static properties and thermo-mechanical fatigue performance. It was found that the solidification time is very important for both the static and thermo-mechanical performance. If the solidification time is long the properties are controlled entirely by the large graphite flakes and there is no influence of the alloying elements. On the other hand if the solidification time can be kept short the need for alloying elements may be removed. For the shorter solidification times an influence from the matrix and thus the alloying elements can be seen. It was found that molybdenum enhances TMF-life while no such effect was found for niobium. Niobium, on the other hand, has a larger effect on static strength than molybdenum and also on the cyclic stress in the thermo-mechanical fatigue experiments.
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