ABSTRACT Salt-spray test procedures are frequently used in industrial practice as a test method for proof of product quality of semi-finished products and received tested parts with regard to their corrosion resistance. For this reason, salt-spray testing is one of the most wellestablished corrosion test procedures. However, no statement can be made about the way in which corrosion develops over time (linear, exponential or logarithmic). Furthermore, the test conditions for salt-spray tests are intensified in order to shorten the testing periods, which can lead to a change in the corrosion mechanism. Nevertheless, saltspray testing can be brought to a qualitatively higher level and the clarity of the results can be improved by means of in-situ electrochemical noise measurements. In contrast to established electrochemical tests, in which specimens are surrounded by a common bulk electrolyte, electrochemical measurements in the spray chamber are based on the development of an electrolyte film not only on the surface of the specimen, but also on the inside walls of the testing chamber, and on all fittings present (e.g. specimen holder). The measured effect, thus, has the same basis as in conventional electrochemical measurements. The exploitable signal is limited by the shortest connection route between the specimens, as well as by the thickness and the conducting ability of the electrolyte film. The successful application of noise measurements under salt-spray conditions is shown on various examples for corrosion testing. Additional in-situ videomonitoring was also applied.
INTRODUCTION Salt-spray testing is the most common "corrosion test method" in the industry. However, it has been rightly under criticism for long time. The by default long test periods of at least 96 hours (often also several hundreds to about one thousand hours) is disadvantageous for the user. This is generally accepted, however, since the salt-spray testing is believed to provide the possibility to assess the long time corrosion behaviour. But it´s completely disregarded that the corrosion mechanism under salt-spray conditions almost never corresponds with the corrosion behaviour under practical conditions1. False estimations and wrong or unfavourable material choices are the consequence. It is an urgent task to find new ways of examination to raise this testing procedure to a higher standard, to increase the meaningfulness, and to shorten the test periods. Different solutions may be possible. One possibility is the application of approved electrochemical corrosion test procedures to practical examining tasks. This already gains acceptance. Simple potential and current measurements, the polarization measuring technique, as well as impedance measurements and the noise diagnostics have to be mentioned2. Noise measurements are useful for a faster examination, since it can show the beginning of the corrosion before a macroscopically visible damage arises. A number of successful applications confirm the high potential of this method3-7. Another possibility is the combination of salt-spray methods with known and approved measurement techniques of electrochemical corrosion and materials testing. This can be regarded as corrosion monitoring within a laboratory. The basis for electrochemical examinations under salt-spray conditions is the electrolytic contact between the specimens and the reference electrodes in the test room, which arises from the electrolytic film developing during the operation of the spraying chamber. Further problems, like bonding and arrangement of the specimen, constancy of the chamber parameters, realization of continuously, correctly recording, and assessing electrochemical data, as well as the accompanying add