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  • The use of electrochemical noise for detection of stress-corrosion cracking in austenitic stainless steel
    Kovač, Jaka, 1981- ...
    It is known that stress-corrosion cracking (SCC) is a complex process, becauseit causes the initiation and propagation of cracks by the synergistic action of mechanical stress and corrosion ... reactions. Three different sets of experiments regarding SCC detection performed in our investigations are shown in this work. The selected experiments follow from the easiest system to detect SCC to the hardest system to detect SCC regarding material SCC susceptibility. he first example shows measurement that was made during SLRT tests on stainless steel 304, where specimens were taken from an old boiler. Aclear relationship between specimen elongation rate, which is related to crack growth and electrochemical noise signal, was found in this research. n the basis of clear detection of SCC processes another set of measurements was performed on stainless steel 304 exposed to constant load test at room temperatures. In this case, material with better quality - more homogeneous with no large defects, was used. Both transgranular and intergranular SCC modes were investigated separately by using different corrosion solutions. Results of measured electrochemical noise, elongation of specimen and acousticemission showed a successful detection of SCC event during transgranular stress-corrosion cracking propagation by simultaneous use of allthree methods. In the case of intergranular SCC propagation on the same type of steel, no such events were detected, but it was observed that the process could be detected as an accumulation of several small steps.After positive results from previous tests, further set of experiments was performedon highly SCC sustainable stainless steel (AISI 304L). Measurements were realized during SLRT tests. In results a clear differentiation between active corrosion processes during steel exposure to aqueous solution of ammonium thiocyanate was compared to low corrosive action in steel exposed to aqueous solution of sodium thiosulphate. The difference in intensity of corrosion processes could be clearly seen from electrochemical noise measurements. n the basis of our research, it can be concluded that EN is promising method that can be use for detection of SCC processes on different quality stainless steels. In case of a highly SCC susceptible material the detection was clear and even relation between measured EN spikes and displacement rate was observed. The method in combination with acoustic emission technique and elongation measurement also showed its ability to detect individual SCC event in case of discontinuous transgranular SCC processon specimens made from high quality stainless steel AISI 304. On the other hand in case of smoother intergranular SCC propagation, observed on the same kind of stainless steel, only an accumulation of SCC processes was detected. The experiments performed on low SCC susceptible stainless steel 304L also showed that the detection of corrosion processes are possible with EN method, but the main difficulty concerning detection of SCC by EN signals was distinguishing between different corrosion processes, especially pitting processes and crack propagation processes. However, the use of additional techniques, as acoustic emission and elongation measurement, was found to be useful for distinguishing of those two processes.
    Source: Book of abstracts (Str. 77-79)
    Type of material - conference contribution
    Publish date - 2008
    Language - english
    COBISS.SI-ID - 1418087

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