Anodic treatment of galvanic Zn-Ni alloy coatings
Wydział Chemiczny, Politechnika Śląska, Gliwice
Instytut Katalizy i Fizykochemii Powierzchni PAN, Kraków
This work is connected with anodic oxidation of galvanic Zn-Ni alloy coatings in alkaline baths which were saturated hydrous solutions of three hydroxides of alkaline earth metals, i.e.: Ca(OH)2, Sr(OH)2 i Ba(OH)2. Investigation of surface structure of the anodized Zn-Ni coatings by means of scanning electron microscopy (SEM) as well as their chemical composition by X-ray photoelectron spectroscopy (XPS) have been done within the framework of the studies. The corrosion resistance studies in sodium chloride solution by potentiodynamic method (LSV) have been also made. On the basis of the obtained results it was found that the process of anodic oxidation in the solutions leads to formation of oxide and hydroxide character coatings which influence the corrosion resistance improvement.
Keywords: zinc-cobalt coating, Zn–Ni alloy, anodic oxidation
Vol. 59, nr 10
The influence of Pb addition in zinc bath on the corrosion resistance of coatings
Politechnika Śląska, Instytut Nauki o Materiałach, Katowice
In the paper the results of tests defining the influence of Pb addition in a zinc bath on the corrosion resistance of obtained coatings are presented. The coatings for the tests were produced on low silicon steel in zinc bath containing 0.4; 0.8; 1.2% wt. Pb Corrosion resistance of coatings obtained in alloy baths was compared with the corrosion resistance of a coating obtained in a bath of pure Zn. The structure of coatings has been developed, the coating thickness has been established. Corrosion resistance of the coatings was defined by comparative methods in a standard corrosion test in neutral salt spray and in moist atmosphere containing sulphur. The tests in salt spray were carried out in accordance with the PN-EN ISO 9227 standard. Corrosion tests in moist atmosphere containing SO2 were performed in accordance with the EN ISO 6988 standard. It has been established that Pb additions to a zinc bath can decrease corrosion resistance of obtained coatings. The corrosion resistance decreases with increasing Pb content in zinc bath.
Keywords: hot dip galvanizing, zinc baths, corrosion resistance
Vol. 59, nr 10
Corrosion monitoring of the internal surfaces of tubing in shale gas wells
Department of Chemistry and Corrosion of Metals, Faculty of Foundry Engineering,
AGH-University of Science and Technology, Cracow, Poland
Materials Design Division, Faculty of Materials Science and Engineering,
Warsaw University of Technology, Warsaw, Poland
A corrosion monitoring station was designed and built into a shale gas extraction pipeline. The station is universal and can be used in conventional oil and gas extraction systems. The device has been tested on wells in operational conditions during the fracturing process in Wysin 3H (flowback, flow stimulation with gas lift). The station’s operating pressure ranged from 3 to 40 bar for unsettled outflow of liquid and gas from the well. The proposed monitoring station makes it possible to carry out corrosion (LPR, EIS, ER), as well as physico-chemical (pH, redox potential) “on-line” measurements during the operation of a gas well. Laboratory and field tests have shown that the impedance method of measuring the polarization resistance is sensitive enough to allow both the monitoring of the corrosion rate (including pitting corrosion) as well as the performance of studies that help in the selection of materials and inhibitors.
Keywords: shale gas, corrosion, monitoring
Vol. 59, nr 10
Effect of some metallurgical variables on the corrosion fatigue behavior of α-brass in sodium nitrite solution
YOUSSEF G. I.
KHORSHED L. A.
ASHOUR E. A.
Electrochemistry and corrosion Lab., Physical Chemistry Dept., National Research Centre, Dokki, Cairo, Egypt
The corrosion fatigue behavior of three metallurgical conditions of α-brass (as- received, cold- rolled and annealed) in 1 M NaNO2 solution under free corrosion potential and under a constant applied anodic potential of 300 mVNHE (Normal Hydrogen Electrode) was investigated by applying the reverse bending technique at 70 cycle /min. The fatigue life and fatigue strength of α-brass in 1 M NaNO2 solution under free corrosion is considerably shorter than that obtained in air, while under applied anodic potential value 300 mVNHE a further reduction in fatigue life was obtained. The longest fatigue life is that corresponding to the cold- rolled followed by the fatigue life of the as- received and finally the fatigue life to the annealed specimens. The same order was also obtained in sodium nitrite solution at the free corrosion condition as well as under the applied anodic potential. The fracture mode of the fatigued specimens changed from transgranular in air to mixed inter-and transgranular in nitrite solution for the as- received and cold- rolled. Annealed specimens show a mixed mode in both air and nitrite solution. The conjoint action of film rupture and adsorption models is the operating mechanism of corrosion fatigue of brass in nitrite solution.
Keywords: corrosion fatigue, fatigue life, fatigue strength, sodium nitrite, α-brass
Vol. 59, nr 10