Evaluation of corrosion resistance of two engineering alloys in molten salts by electrochemical techniques

The electrochemical behaviour of two steels typically used in power boilers has been studied in the temperature range from 540°C to 680°C. Two environments were used: a) a synthetic salt mixture of 80% V2O5 − 20% Na2SO4 and b) oil ash collected from a high temperature reheater. Corrosion rates obtai...

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Bibliographic Details
Published in:Materials and corrosion 2003-01, Vol.54 (1), p.32-36
Main Authors: Martínez-Villafañe, A., Almeraya-Calderón, F., Gaona-Tiburcio, C., Chacón-Nava, J., González-Rodríguez, G.
Format: Article
Language:English
Subjects:
Applied sciences
boiler tubes
Corrosion
Corrosion tests
engineering alloys
Exact sciences and technology
hot salt corrosion
Kesselrohre
Korrosin in heißen Salzen
Metals. Metallurgy
natural oil ash
natürliche Ölasche
potentiodynamic polarisation curves
potentiodynamische Polarisationskurve
synthetic salt
synthetisches Salz
Tafel slopes
Tafelsteigungen
technische Legierungen
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Summary:The electrochemical behaviour of two steels typically used in power boilers has been studied in the temperature range from 540°C to 680°C. Two environments were used: a) a synthetic salt mixture of 80% V2O5 − 20% Na2SO4 and b) oil ash collected from a high temperature reheater. Corrosion rates obtained from electrochemical potentiodynamic polarisation curves (Tafel extrapolation) were compared for both steels exposed in each environment. The results showed that increases in temperature resulted in higher corrosion rates, being this effect most notorious above about 620°C. In the synthetic salt, and at temperatures up to about 580°C, both steels showed similar behaviour. With further increases in temperature, the T22 steel was less resistant and, at the highest temperature used here, its corrosion rate was almost seven times higher than that measured for the 347H steel. The results obtained with the natural oil ash for the T22 steel showed a dramatic increase in corrosion rate as temperature goes up over the range used. For the 347H steel, and up to about 580°C, the corrosion rates were similar to those obtained with the synthetic salt. Above 580°C, the corrosion rate measured increased slightly with temperature, being at 680°C about 2.5 times higher than that found by using the synthetic salt. Therefore, an important difference in corrosion rates has been found depending upon the corrosive salt used. This is an important result because imply that, at least for materials used in fossil power plants, more realistic data can be obtained by using natural ashes in the experimental work. Beurteilung der Korrosionsbeständigkeit von zwei technischen Legierungen in geschmolzenen Salzen mit Hilfe elektrochemischer Verfahren Das elektrochemische Verhalten von zwei typiscshen Stählen für Kraftwerkskessel wurde im Temperaturbereich zwischen 540°C und 680°C untersucht. Zwei Umgebungen sind eingesetzt worden: a) synthetische Salzmischung aus 80% V2O5 − 20% Na2SO4 und b) Ölasche, die von einem Hochtemperaturzwischenüberhitzer gesammelt wurde. Aus elektrochemischen potentiodynamischen Polarisationskurven (Tafelextrapolation) ermittelte Korrosionsgeschwindigkeiten sind für beide Stähle in jeder der beiden Umgebungen verglichen worden. Die Ergebnisse zeigten, dass eine Zunahme der Temperatur zu höheren Korrosionsgeschwindigkeiten führt, wobei dieser Effekt am ausgeprägtesten für Temperaturen oberhalb etwa 620°C ist. In dem synthetischen Salz und bei Temperaturen bis zu etwa
ISSN:0947-5117
1521-4176
DOI:10.1002/maco.200390003