The impact of the number of exposures of the test-plates on the error of determination of corrosion effect of the cooling liquid

The results of repeated serial comparative laboratory studies of the corrosive effects of different coolants (OZh-40 and KhNT-NV-40) based on ethylene- and propylene glycol, respectively, are presented. A significant discrepancy is revealed between the obtained results according to accepted and approved procedures for the test-plates continuously exposed for 336 h at a temperature of 88 ± 2°C in the same batch of test antifreeze. The current standards do not regulate the frequency of their using, i.e., the number of exposures of the control samples of the main groups of ferrous and non-ferrous metals, but only limit their thickness, which is naturally reduced due to corrosion and routine cleanings. The use of highly effective corrosion inhibitors in antifreezes allows the plates to be kept within the permissible thickness for about 10 tests, however, the relative error of assessing the corrosion effect between parallel series significantly increases. Strengthening of the requirements to the operational safety and depreciation period of heat exchange equipment, systems and production complexes, development and conversion of the new heating agent and coolants entails the necessity of elimination of the system errors in the tests, the results of which are used by design engineers, developers, manufacturers and consumers. Corrosion tests of the coolants showed that the number of exposures of the test plates affected the accuracy of the obtained data. Recommendations regarding limitation of the number of plate exposures and, accordingly, elimination of the system errors and ensuring an acceptable error in determination of the corrosion rate (corrosion effect) are specified with the goal to increase the accuracy of the corrosion measurements upon production and operation monitoring, as well as the efficiency of the selection of antifreeze and additives to them.

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