Vízügyi Közlemények, 1958 (40. évfolyam)

4. füzet - VII. Kisebb közleménye

f 24) Verlegung fordert Taucherarbeit, d

) die Isolierung des Brunnens kann unter Wasser nicht kontrolliert werden. Auf Grund des Vergleichs der Vor- und Nachteile ist es am richtigsten, den Flußbettbrunnen in 2,50 m Höhe über dem lokalen niedrigsten Wasserstand bei Niederwasser zu erbauen (Abb. 17). Die Ergiebigkeit der vom Schiff erbauten Rohrbrunnen mit doppeltem Kiesfiltermantel (b), sowie der am Ufer erbauten Rohrbrunnen, deren Filterschicht durch Entsandung hergestellt ist («), wurde durch Pumpversuche verglichen (Abb. 18). Die Ergebnisse wiesen dahin, daß die letzteren Brunnen um 22% weniger Wasser ergeben, aber ihre Bauzeit fünfmal, ihre Kosten viermal geringer sind, als die der vom Schiff aus erbauten Rohrbrunnen mit Kiesfilter. Die Ausbeulung sehr hartes Wasser enthaltender Uferzonen könnte z. B. mit Flußbettbrunnen vorteilhaft sein, da der Nachschub hauptsächlich vom Fluß her zu erwarten ist. Eine Verringerung des Eisengehaltes des Wassers ist nicht recht zu erwarten, da er in den meisten Fällen von der Oberfläche des Flußsohlenmaterials abstammt. (/.usammenfassung des Verfassers, deutsch von Dipl. Ing. K. Fazekas) PROTECTION OF DRILLED WELLS AGAINST CORROSION by Sz. Pupp (See pp. 96—106 in Hungarian Text) UDC. 620.197:628.112.2 Drilled wells play an important part in the drinking and processing-water supply of Hungary, though the use of their water is considerably limited by the significant iron content in 65 percent of them. According to investigations, at the major part the iron content does not originate from the water-bearing formation, buL is dissolved from the iron tubing ol the well owing to the aggressivity of water. The relation between the inherent (equilibrium) carbon dioxide and Lhe calcium hydrocarbonate content i.e. Lhe carbonate hardness of Lhe water shows Lhat generally strong aggressive properties are characleristic of soft waters with tow mineral content owing to their free carbon dioxide contents. Therefore the carbonate hardness of Lhe water plays a significant part in Lhe aggressive effect on iron and other mêlais. Like all mêlais, iron has a certain solution potential, a tendency to change his metallic state into an ionic one, i.e., to dissolve. During this process the positive charge of hydrogen ions in the water is neutralized by admitting electrons, the hydrogen atoms without charge accumulate on the surface of the iron and form a coating. In this case we say that the iron is polarized and resisls the electrochemical solution. When, however, due to external conditions or to the lowering of Lhe pH value of water the atomic hydrogen on the surface of the metal changes into molecular form, iL is liberated in Lhe form of gas and the solution of the metal continues. If the pH value exceeds the 7,7 limit, the iron remains practically stable, while under this point the water must be considered aggressive against iron. Should the water contain dissolved oxygen, the developping atomic hydrogen layer will oxydize, i.e., Lhe iron depolarize, the iron surface will not be protected against Lhe further release of electrons and from further dissolution. Still, the depolarization is more essential for protecting the metal with respect to corrosion. In fact, when the iron dissolves, the hydrogen ions, by admitting electrons, turn into hydrogen atoms and, at the same time, hydroxil ions remain in lhe solution in equivalent quantity. Thus an alcalic film is formed along the metal surface, and the inner area, the water-side of the tube will be alcalized. The hydroxil ions formed along the wall bind the free carbon dioxide of water, and thus calcium carbonate precipitates. This yields, together with the ferrihydroxide, formed by the influence of dissolved oxygen, the principal ingredients of the natural protective layer. Therefore, the presence of dissolved oxygen in water (at least 5 mg/1) is essential to the development of protective layer. Thanks to this recognition, the creation of an artificial protective layer was made possible because the atomic hydrogen - as revealed by Jendrassik — may be removed from the iron surface also by other chemical oxydative substances dissolved in water. Author applied this procedure to several drilled wells and observed, that