Spannstiihle kiinnen wiihrend der Verarbeitung auf Baustellen korrosiven Bclastungen ausgesetzt sein, die zu einer Gefahrdung der S t a l e durch wasserstoffinduziertc SpannungsriRkorrosion fuhren kann. Marktubliche filmbildende Korrosionsschutzmittel wurden durch elektrocheniische Untersuchungen und Dauerstandversuchc im Hinblick auf ihre Eignung als temporare Korrosionsschutzmittel untersucht. Die Ergebnisse zeigten, daR zwci der in die Untersuchung einbezogenen Mittel eine risikolose Anwendung im Spannbetonbau ernioglichen.Prestressing steels may be subjected to corrosive conditions during the manufacturing process at building sites. Due to this a risk of hydrogcn induced stress corrosion cracking of the steels may arise. Electrochemical investigations and constant load tests have been carried out to show the suitability of different film forming coatings to be applied as temporary corrosion protection measures. The results indicated the applicability of two agents involved in the investigations without any risk for post tensioning purposes.
Stainless steel ground anchors are still rarely used in Europe. A project was initiated to demonstrate the technical and economic performance of stainless steels for such applications.
Three different steel grades were examined, i.e. two austenitic grades 1.4311 (‘304LN’) and 1.4406 (‘316LN’) and one duplex grade 1.4362 (‘2304N’). All of them had low carbon contents (< 0.03%) and were alloyed with nitrogen to improve their strength properties.
Different electrochemical tests were carried out to assess the performance of stainless steel in chloride/sulphate environments. The results confirmed that the investigated stainless steels may be employed for a wide range of corrosive ground anchor environments.
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Im Holz vorhandene Essigsaureester konnen in Gegenwart von Wasser zu freier Essigsaure hydrolisieren. Diese Essigsaure wirkt auf verschiedene Metaile bei direktem Kontakt mit Holz korrosiv. Sie kann weiterhin wegen ihrer Fluchtigkeit auch Metalle im Darnpfraum in der Nahe von Holz beeinflussen. Der Gehalt an Essigsaureestern, die Bildungs-und Freisetzungsraten von Essigsaure sind holzartspezifisch. Femer ist die Bildungsrate als hydrolytischer Vorgang stark feuchtigkeits-und temperaturabhangig. Je nach Behandlung, Vorgeschichte und Art bleibt die Aggressivitat eines Holzes iiber Jahre erhalten. Holzschutzchemikalien, insbesondere in Form wafhiger Salzlosungen, konnen in gewissem Umfang die Aggressivitat eines Holzes erhohen. Das Korrosionsnsiko in der Praxis fur Metallteile in direktem Kontakt mit Holz hang stark von den Einsatzbedingungen, d.h. von Luft-und Holzfeuchtigkeit ab. Es ist in geschlossenen Gebauden gering. Bei hohem Feuchtigkeitsangebot sind korrosionsbestandigere Werkstoffe, wie z.B. Chrom-und Chrom-Nickel-Stahle zu venvenden.Wood contains acetic acid ester, which hydrolyses in the presence of water to give free acetic acid. This acetic acid acts as a corrodent to several metals in contact with wood and in the vapour space near wood surfaces because of the volatility of the acetic acid. The quantity of acetic acid ester, the rate of formation and emission of acetic acid is specific for the species of wood. Moreover the rate of formation, as a hydrolytical reaction, is strongly effected by moisture and temperature. According to treatment and species, wood may retain its corrosivity for many years. Wood preservatives, especially salt solutions, are able to increase the corrosivity to a certain degree. The risk of corrosion of metals in practical services depends on environmental conditions, i.e. relative humidity and moisture content of wood. In covered buildings under indoor conditions the risk is relatively small. If the humidity and the moisture content of wood are high, corrosion resisting metals, e.g. ferritic or austenitic stainless steel, should be used.
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