The article summarizes state of the art of the influence of external layer of Fe-Zn intermetallics on corrosion behaviour of galvanized steel in a fresh, hardened and chloride contaminated concrete. Current point of view on formation, composition and crystallography of particular intermetallic Fe-Zn phases, that are present in hot dip galvanized coating. External factors as alloying elements are involved as well. A corrosion resistance of these intermetallic layers (especially ζ-FeZn13) during exposure in concrete is evaluated finally.
A. Faltýnková, M. Hruška, J. Kudláček, M. Valeš and P. Szelag
The study is focused on evaluating hydrogen charging of materials in plating baths approved for aviation and in weak acid plating baths. For the evaluation, ASTM F519, ASTM F326 and a newly patented method of measuring device PCN1 - Pulsator cyclic loading were used. ASTM F519 is time consuming and the results are difficult to compare. ASTM F326 proved to be unsuitable for testing above plating baths because of strong hydrogen embrittlement of probes and thus their destruction. Conversely, the PCN1 method was fast and reproducible. Results showed that the baths approved for aviation caused stronger hydrogen embrittlement than weakly acidic zinc baths.
Accelerated corrosion testing is indispensable for material selection, quality control and both initial and residual life time prediction for bare and painted metallic, polymeric, adhesive and other materials in atmospheric exposure conditions. The best known Neutral Salt Spray (NSS) test provides unrealistic conditions and poor correlation to exposures in atmosphere. Modern cyclic accelerated corrosion tests include intermittent salt spray, wet and dry phases and eventually other technical phases. They are able to predict the material performance in service more correctly as documented on several examples. The use of NSS should thus be restricted for quality control.
Polarization curves measured in a sufficiently aggressive environment (e.g. 0.5 mol dm−3 of H2SO4) may help to assess corrosion resistance of stainless steels. New phases precipitate in steel exposed long-term to high temperatures, which may affect the corrosion resistance. Potentiostatic polarization curves were measured on austenitic steel Super304H in a solution annealed state (from the producer) and in a state aged for 15 000 hours at temperatures of 650, 675 and 700 °C. The higher level of current density in passivity (worse corrosion resistance) was reported after aging at 650 °C.
M. Blahetová, J. Horák, P. Kubesa, S. Lasek and T. Ochodek
The case study of chimney liner corrosion addresses three specific cases of damage of chimney systems from of stainless steels. These systems were used for flue of gas arising from the combustion of brown coal in small automatic boilers, which are used for heating. Detailed analyzes implied that the cause of devastating corrosion of the steel AISI 316 and 304 steel (CSN 17349, 17241) was particularly high content of halides (chlorides and fluorides), which caused a severe pitting corrosion, which led up to the perforation of the liner material. Simultaneous reduction of the thickness of the used sheets was due to by the general corrosion, which was caused by the sulfur in the solid fuel. The condensation then led to acid environment and therefore the corrosion below the dew point of the sulfuric acid has occurred. All is documented by metallographic analysis and microanalysis of the corrosion products.
J. Brezinová, J. Koncz, D. Draganovská and A. Guzanová
The paper presents results of research aimed at determining the corrosive properties of steel with cathode metal coating in selected corrosive environments. The corrosion properties of the tin coated steel were evaluated using electrochemical impedance spectroscopy and potentiodynamic tests. For realised measurements, distilled water, 0.5 mol dm−3 NaCl solution, 0.1 mol dm−3 NaCl solution and SARS, which simulates acid rain were used as corrosive solutions. Both corrosion methods are suitable for diagnosing corrosion properties of steel with metal coatings.
The study summarises current knowledge on microbial corrosion in a deep nuclear-waste repository. The first part evaluates the general impact of microbial activity on corrosion mechanisms. Especially, the impact of microbial metabolism on the environment and the impact of biofilms on the surface of structure materials were evaluated. The next part focuses on microbial corrosion in a deep nuclear-waste repository. The study aims to suggest the development of the repository environment and in that respect the viability of bacteria, depending on the probable conditions of the environment, such as humidity of bentonite, pressure in compact bentonite, the impact of ionizing radiation, etc. The last part is aimed at possible techniques for microbial corrosion mechanism monitoring in the conditions of a deep repository. Namely, electrochemical and microscopic techniques were discussed.
The paper deals with electrochemical deposition of coatings of highly entropic alloys. These relatively new materials have been recently intensively studied. The paper describes the first results of electrochemical coating with highly entropic alloys by deposition from non-aqueous solutions. An electrochemical device was designed and coatings were deposited. The coatings were characterised with electronic microscopy scanning, atomic absorption spectrometry and X-ray diffraction methods and the combination of methods of thermic analysis of differential scanning calorimetry and thermogravimetry.
To begin with, the intorduction of this paper summarises literature sources that wrongly interpret results of the bond strength between hot-dip galvanised reinforcements and concrete. The influence of the total reinforcement anchorage length on the bond strength results assessment was studied in detail. The numeric analysis of beam models with various testing anchorage lengths (the analysis input data comprised the results of previous bond strength tests carried out in a laboratory) unambiguously confirmed that when the bond strength between concrete and hot-dip galvanised reinforcement with a sufficient test anchorage length is tested in a beam test, the negative impact of the coating corrosion on bond strength with concrete may be biased. It is more objective to test bond strength with concrete in a pull-out test where a very short test reinforcement anchorage length is set out as a standard.
Corrosion tests of both annealed and not annealed bends of HR3C and S304H steels in operation conditions of black and brown coal combustion boilers in EPRU and EDE. After a long-term exposure, the samples were assessed gravimetrically and metallographically. The comparison of annealed and unannealed states showed higher corrosion rates in the annealed state; corrosion of the sample surface did not essentially differ for compression and tensile parts of the beams. Detailed assessment of both steels is described in detail in this study.