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- Self-corrosion (4)
- X-ray tomography (4)
- Concrete parameters (3)
- Concrete (2)
- Pitting corrosion (2)
- Austenitic Stainless Steel (1)
- Carbon steel (1)
- Cathodic Protection (1)
- Cathodic protection (1)
- Chloride Induced Corrosion (1)
Hot cracks as stress corrosion cracking initiation sites in laser welded corrosion resistant alloys
(2005)
Although hot cracks at weld surfaces of corrosion resistant alloys (CRAs) might provide access to respective aggressive media and thus, might provide the conditions for a local potential and pH drop, the interaction between hot cracking and corrosion phenomena has not been investigated up to the present. This particularly concerns the initiation of stress corrosion cracking inside such crevices.
As a first approach to clarify the influence of hot cracks on corrosion resistance, considering particularly stress corrosion cracking, hot crack afflicted laser welds of three different CRAs have been subjected to a series of different corrosion tests.
Besides the fact that the Drop Evaporation (DE) Test represents a more realistic procedure than standard immersion tests it turned out that hot cracks can obviously represent an initiation site of stress corrosion cracking in the austenitic stainless steel AISI 309 (German No. 1.4828). The susceptibility of such hot crack afflicted laser welds to stress corrosion cracking (SCC) significantly depends on temperature and chloride concentration of the test environment In comparison, the high nitrogen austenitic stainless steel AISI S 34565 (German No. 1.4565) did not exhibit any stress corrosion cracking associated with hot cracking. This material exhibited pitting corrosion and stress corrosion only in the base material. The Alloy 50 (German No. 2.4850), a Nickel based material, was susceptible to pitting corrosion, but showed no tendency towards stress corrosion cracking at all.
Pitting corrosion of carbon steel and iron in chloride containing alkaline environment is already well investigated, although a couple of questions are not clarified satisfactorily. The critical chloride content for steel in concrete and the critical chloride to hydroxide ion ratio for steel in alkaline solutions is still a major concern, considering chloride induced corrosion problems of steel in concrete. Another not satisfactorily clarified point is the repassivation of carbon steel in consequence of cathodic polarization. In the recent literature some indications are shown that repassivation occurs after a certain time of polarization. GLASS [4-9] and PEDEFERRI [1-3] draw the conclusion that the ennoblement of open circuit potentials (OCP) indicates re-passivation effects due to cathodic polarization. SAGÜÉS [10] carried out potentiodynamic repassivation tests and draws the conclusion that the repassivation potential Er is nearly independent of the solution composition, but influenced by severity of corrosion attack and is in the potential range from - 0.8 V to - 0.4 V vs. Saturated Calomel Electrode (SCE). The transferability of SAGÜÉS results to questions concerning cathodic protection (cp) is questionable, as potentiodynamic polarization tests (PPT) give no information on changes induced by long time polarization.
Therefore, the investigations discussed in this paper aim to clarify, to what extend the re-passivation of carbon steel due to cathodic polarization occurs, and if the ennoblement of OCP is a sufficient indication for repassivation. In a first step the corrosion state of five nominal equal test specimens was determined by electrochemical techniques, i.e. electrochemical noise measurements (ENM) and electrochemical impedance spectroscopy (EIS). After determining the initial corrosion state by evaluating the charge transfer resistance and the polarization resistance respectively as well as evaluating potential and current noise signals, the specimens were polarized cathodically. Impedance data were recorded previous to, during and after polarization. The impedance data were evaluated by equivalent circuit fitting with special attention to charge transfer resistances and diffusion properties. The results show that reduction of oxides and oxygen diffusion during cathodic polarization has strong impact on the systems behavior.
Corrosion of steel reinforcement in concrete exposed to chloride containing
environments is a serious problem in civil engineering practice. Electrochemical
methods, e.g. potential mapping, provide information whether the steel reinforcement
is still passive or depassivation has been initiated. By applying such techniques no
information on the type of corrosion, its extent and distribution of corrosion products
is available. Particular the corrosion progress is a significant problem. Especially in
the case of element corrosion in reinforced concrete structures, the development at
the anode can not be separated into corrosion damage causing by element corrosion
or self-corrosion. Until now also in laboratory tests it is impossible to collect such
information without destroying specimens after electrochemical testing was
performed place. To overcome this problem it was tried to study the steel surface
within the mortar specimens by X-ray tomography (CT). Within the scope of these
investigations it could be shown, that X-ray tomography is suitable to make corrosion
pits visible which are embedded in a mortar with a cover thickness of about 35 mm.
In this publication the corrosion damage of reinforced steel is documented timedependent
by X-ray tomography.
Investigations of corrosion on small cathodes in reinforced concrete - observations and suggestions
(2009)
Corrosion of steel reinforcement in concrete exposed to chloride containing environments is a serious
problem in civil engineering practice. The standards and guidelines contain only minimum
requirements regarding concrete quality and concrete cover. In very critical cases, for example the
ingress of chlorides, the application of different coatings is currently the only possibility to protect the
reinforced concrete structures. In this case the modelling of reinforcement corrosion would be more
practical. One sub-project of a DFG-research project (FOR 537) is currently performed at the Federal
Institute for Materials Research and Testing (BAM). Aim of the sub-project is the description of
corrosion propagation and the characterization of the corrosion on specimens with small cathodes by
electrochemical parameters. The electrochemical parameters are determined by suitable
electrochemical measurements, considering concrete parameters as well as different environmental
conditions.
Corrosion of steel reinforcement in concrete exposed to chloride containing environments is a serious problem in civil engineering practice. Electrochemical methods, e.g., potential mapping, provide information whether the steel reinforcement is still passive or depassivation has been initiated. By applying such techniques no information on the type of corrosion, its extent and distribution of corrosion products is available. Particular the corrosion progress is a significant problem. Especially in the case of macrocell corrosion in reinforced concrete structures, the development at the anode cannot be separated into corrosion damage resulting from macrocell corrosion or self-corrosion. Until now also in laboratory tests it is impossible to collect such information without destroying specimens after electrochemical testing was performed. To overcome this problem it was tried to study the steel surface within the mortar specimens by X-ray tomography (CT). Within the scope of these investigations it could be shown, that X-ray tomography is suitable to make corrosion pits and their development visible which are embedded in a mortar with a cover thickness of about 35 mm. In this publication the time-dependent corrosion damage of reinforced steel is documented by X-ray tomography.
The paper presents the damage model of German Research Unit 537 which was used as a working hypothesis for the development of a user-friendly design model. Excerpts from the laboratory experiments and numerical calculations processed in project A of the research unit are presented here. The excerpts include the quantification of self-corrosion, geometrical effects in the macrocell corrosion, development of corroding steel surface and pit depth as well as the quantification of the resistivity of the concrete and the corrosion of steel in cracked concrete.