Einsatz des Wirbelstromprüfverfahrens zur zerstörungsfreien Bestimmung der Angriffstiefe von Korrosionsschäden an Flugzeug Tragflächenbeplankungen

Application of eddy-current method for nondestructive determination of corrosion attack depth at aircraft wing skins A NDI test system for the determination of the depth of corrosion attack in the form of shallow pit formation and pitting is presented. The system is based on the eddy-current method, whereby the signals of a specially developed probe are converted to an image representation, which can he evaluated quantitatively at a PC-screen. The described test system was developed for the field of in-service inspection of aeroplanes. As a first practical operation, the system was tested in co-operation with Daimler-Benz Aerospace at TORNADO aeroplanes. All the described results can be transferred to other test situations with comparable damage mechanisms. Because of the Skin-effect of the eddy current, this method is limited to surface-near areas however. If the test object comes as metal sheets, depth evaluation of corrosion attack on the hidden surface is also possible (even in multi-layered structures).     

Korrosionsschäden an Bronzeplastiken

Corrosion damage of bronze sculptures In order to assess the effect of contaminated air (industrial and urban atmospheres) on bronze sculptures the composition of the base metal and of the corrosion products has been investigated pn a number of sculptures in the open air. in addition to the corrosion products typical of bronze — basic copper sulfate, basic copper nitrate, basic copper chloride stannous acid, lead sulfate — other compounds have been found which — as e.g. gypsum — are formed by reaction between dust and atmospheric contaminats. The corrosion layers usually include several strata; soot containing strata are characteristic of the winter season. Oils, waxes and plastic coating are suitable agents for protecting bronze sculptures against corrosion. The two first mentioned materials are suitable in particular for older bronzes having a natural or artificial patina; they require, however, renewal after regular intervals; plastic coatings are suitable for application to bright metal surfaces and are more durable. Despite the high manpower requirement it is advisable regularly to clean the sculptures with detergent containing water.     

Neue Wege bei der zerstörungsfreien Korrosionsüberwachung von Rohrleitungen

New possibilities of nondestructive pipe corrosion monitoring The perfect function of pipes and vessels is an essential prerequisite for the availability, capacity and security of the equipment in the chemistry and power engineering. The quality assurance of such pipe systems demands careful analysis of the present state including nondestructive testing and stress calculation by the help of FEM, lifetime prediction, and derived from this, specific maintenance. Modern CAD-software gives the possibility to store the results of visual control, of nondestructive testing and of strength calculation directly in the isometry and otherwise retrieve the test result – dates front the isometry. A powerful notebook for ultrasonic measurements was developed, to realize all described actions under field conditions. Trends of corrosion monitoring by electric measurements, polarization resistance measurements, acoustic emission and electrochemical noise measurements are discussed.     

Verwendung nichtmetallischer Werkstoffe zur Verringerung von Korrosionsschäden

Use of non-metallic materials for reducing corrosion damage This paper discusses the application of non-metallic materials for corrosive working conditions. With regard to composite systems metal/non-metal many non-metallic materials nowadays have gained considerable importance. The paper concentrates on non-metallic coatings to protect metals against corrosion hazards. In particular, the groups of materials available, their properties, and the latest developments relating to coating processes are described in detail. It is demonstrated that composite structures have combined the properties of both groups of materials and thus opened up new possibilities for the future.     

Korrosionsschäden an Lagertanks für Salzlake

Corrosion damage at storage tanks for salt brine A tank made of stainless steel type X2CrNiMo17‐12‐2 for intermediate storage of salt brine for cheese production revealed significant pitting corrosion effects shortly after commissioning although comparable units have shown positive long‐term behaviour. By means of electrochemical laboratory tests it could be demonstrated that the observed pitting corrosion was caused by the use of an oxidizing agent for desinfection purposes.     

Untersuchung von Korrosionsschäden mittels β-Rückstreuung

A study of corrosion with β-reflection The application of the β-reflection method in corrosion research is based on the relation between reflection coefficient and atomic number and coating thickness of the reflecting material, the effective atomic number of the corrosion products formed on the metal surface during atmospheric corrosion being always smaller than the atomic number of the particular metal (exception: Be). As far as atmospheric corrosion of steel is concerned, good agreement has been obtained between calculated and measured values of the effective atomic number only after heating to 500° C, because water and carbonate are removed at that temperature. Another condition governing application to corrosion research is uniformity of attack and uniformity of composition of the corrosion products. As to the sensitivity and accuracy of the measurement it is useful not to employ radiation sources having too high a radiation energy.     

Durch Industrieemissionen verursachte Korrosionsschäden an Stahlbauten im Industriegebiet Ostrava

Corrosion due to the action of industrial emissions on steel structures in the industrial region of Ostrava (?SSR) In order to obtain — at least approximative — data allowing a calculation of the financial losses attributable to corrosion the author has undertaken an investigation into such losses; the study is based on an assessment of steel structures, and in particular bridges, gas containers, aerial line lattice poles and mine hauling towers. In this connection the economies have been assessed which may be obtained by coatings (including the periodical renewal of these multilayer systems). It is shown that the periodical repair of the coating systems yields considerable economical advantages when compared to the renewal of the uncoated structure after a service life admissible from security considerations. The useful life could be extended to three times its value by appropriate coatings the cost of which would not exceed one third of the total cost of a structure.     

Korrosionsschäden am Förderband eines Ofens zur Reinigung von mit organischen Chlorverbindungen kontaminiertem Erdboden

Corrosion damage to the conveyor belt of a furnace for the removal of soil from organic chlorine compounds This paper reports the corrosion behaviour of metallic materials which were used in components of a conveyor belt of a decontamination furnace or of which specimens were attached to the belt for testing purposes. The furnace was used for decontaminating soil containing organic chlorine compounds. A total of 1 ferritic and 8 austenitic steels, 9 nickel base alloys, 2 east steels with 15 % Si and 15 % Si + 5 % Cr respectively, and 3 aluminised steels were tested and afterwards investigated by metallographic and micro-analytical methods. Most of the materials failed due to external and/or internal corrosion, preferentially along grain boundaries. The 2 cast steels revealed fairly good corrosion resistance. The material 2.4061 (LC-Ni 99.6) displayed surprisingly good behaviour, however it remains to be seen whether the inward migration of O and C along grain boundaries causes embrittlement. The materials 2.4610 and 2.4831, containing 14-17 % Mo and 8.5-9,5 % Mo respectively, showed good resistance. The reason for this good corrosion resistance could not be clarified. One reason may be the relatively high Mo content but other materials with a comparable Mo content, like materials 2.4856 and 2.4663, were significantly attacked. It appears necessary to check the long-term behaviour of these two materials.     

Untersuchung der Korrosionsschutzwirkung von Wärmeträgern Teil 1: Chemische Prüfungen,Screening- und Spezial-Tests

Testing the corrosion protection of heattransfer fluids Part 1: Chemical, screening and special tests As supplement to AGK Arbeitsblatt W l “Corrosion testing in heat-transfer fluids of solar heating installations” the different methods applied for testing the corrosion protection in heattransfer fluids provided with anti-freeze mixtures on glycol basis have been checked. The coupon tests corresponding to ASTM D 1384, the EMPA-Test, special tests according to ASTM D 4340 as well as the FVV-Heat-Test were part of these investigations. The investigations were carried out with steel, cast iron, two wrought aluminium alloys, one cast aluminium alloy, with copper and brass as well as with tin solder in non inhibited as well as inhibited heat carriers. The non inhibited heat-transfer fluids were composed of water with ethylene and propylene glycol, the others were made up with antifreeze concentrates prefabricated by well known producers. All investigated products provide excellent protective qualities against corrosion. The coupon test according to ASTM D 1384 has been the most effective of all methods tested up to now. This article will be continued.     

Elektrochemische Korrosionsprüfungen an Siliziden der Übergangsmetalle

Electrochemical corrosion testing of transition metal silicides The corrosion resistance of transition metal silicides has been determined with the convenient electrochemical method by Stern and Geary where the measurement of the anodic dissolution current density enables conclusions to be drawn to corrosion resistance. Excellent agreement has been obtained with data published before and having been obtained by the conventional wet chemical methods. The electrochemical method can therefore be used also for the investigation of metallic compounds and high alloy metallic materials respectively. Beyond corrosion data already known for disilicides it has been possible to obtain data for a num-ber of silicides having lower silicon contents. As may be expected the resistance of these silicides is lower than that of the disilicides; however, even these lower silicides may still be termed resistant (attack below 1 g/m²·day). With the exception of MoSi₂, and WSi₂ where no protective SiO₂, layers are formed because of the formation of soluble heteropolyacids of silicon, the disilicides are highly resistant (attack below 0.5 g/m₂d).     

Verhinderung von Anstrichschäden auf Baumaterialien durch Silicon-Bautenschutzmittel

Prevention of damage to the coating of building materials by means of silicon building preservatives Normal dispersion paints applied to brickwork tend to develop cracks and cannot prevent the penetration of rainwater into the cracks, and therefore into the brickwork. This calls for an additional primer. But primers merely solidify the coating, without hindering the penetration of water. With the aid of silicon primers, or primers containing silicon, however, the suction effect of the cracks can be obviated so that damage to the coating can be prevented. The adhesion of the finishing coats on the new primers is equivalent to that on conventional primers.     

Korrosionsschäden in Verbindung mit gelöteten Plattenwärmeübertragern aus nichtrostendem Stahl

Corrosion damage in connection with brazed plate heat exchangers made of stainless steel With increasing time of operation the number of damage to brazed plate heat exchangers made of stainless steel for heating of drinking water as well as to galvanized steel tubes behind the exchangers increase. The heat exchangers suffered from leakages and bulgings. Tubes are assumed to suffer from copper induced pitting. The cause for the damage to the exchangers is galvanic corrosion of copper braze. Investigations of copper contents in the hot water behind the exchanger and in the surface layer of tubes gave no clear results. But the analyses show that pitting of galvanized tubes can possibly be accelerated by liberating copper from the braze to the water.     

Über den Duktilitätsverlust von Blechzugproben aus TiAl6V4 und TiAl6V6Sn2 im Zeitstandversuch bei gleichzeitigem Korrosionsangriff durch NaCl ab 200° C

The loss in ductility of tensile plate specimens of TA16V4 and TiA16V6Sn2 during the creep test with simultaneous attack by NaCl above 200 °C A has been demonstrated by com prehensive research the hot salt corrosion of titanium is due to embrittlement by hydrogen absorbed via intermediarily formed HCl. HCl is probably formed by pyrohydrolysis of AlCl₃ · 6 H₂O the formation of which is highly probable in Al-bearing Ti alloys and which melts at 193 ° C. Beyond that it seems to be established that Al as an alloying addition accelerates hot salt corrosion of Ti by accelerating the formation of chlorine which not only destroys the passive layer on Ti but, through direct attack of grain boundaries and accumulated dislocations gives rise directly to stress corrosion cracking. In order to improve the stress corrosion resistance of Ti the Al content is reduced and other alloying elements such as e. g. Mo, Zr and Si are added; the latter have just little influence on the corrosion behaviour of Ti but, by improving the strength and the long-term stability amy compensate for the reduced Al-content.     

Über einige den Massenverlust durch Korrosionserrosion betreffende Faktoren

Some factors concerning the mass losses by erosion corrosion Corrosion erosion depends on mechanical as well as corrosive actions of the particular medium. As is shown by the results of experiments with carbon steel, stainless steels and aluminium alloys the velocity of the solid particle as well as their quantity and sizes play an important part. In cases of turbulent flow the loss depends but little on the hydraulic properties of the liquid (sulfuric, hyrdrochloric acids, sodium chloride solution etc) while corrosion effects may differ considerably. Additions promoting the formation of solid corrosion products give rise to increase erosion corrosion as soon as an existing protective layer has been removed. The relation between local abrasion and circumferential velocity allows the transfer of results from the model to practice; this possibility enables the duration of the experiments to be reduced: abrasion losses found at high velocities can be used to calculate the losses to be counted with a lower velocities.     

Über den Einfluß verschiedener Chloridionenkonzentrationen auf die Aktiv-Passiv-Korrosionsempfindlichkeit von Stahl in gesättigter Kalziumhydroxidlösung

Influence of various chloride ion concentrations on the active-passive corrosion susceptibility of steel in saturated calcium hydroxide solution The corrosion of steel in concrete is caused mainly by the presence of chlorides. This effect was investigated by measuring potentiodynamic current-voltage-curves and by potentiostatic experiments of stressed (55 or 77% σ_B) plain steel electrodes in saturated Ca(OH)₂-solution with varying chloride concentrations. The results show that down to Cl′-concentrations of 100 mg/l there is a significant statistical probability of corrosion within 48 hours, and that for longer times the threshold concentration may be even lower. The microscopical examination of corroded samples shows that under the experimental conditions only pitting corrosion is the cause of failure and that this pitting is promoted by the applied stress.