BS ISO 18089:2015 pdf download – Corrosion of metals and alloys — Determination of the critical crevice temperature (CCT) for stainless steels under potentiostatic control.
5.6 Temperature measurement instrumentation capable of measuring the temperature of the test solution with an accuracy of ±1 °C. 5.7 Crevice formers or specimen holders of different types can be used in this International Standard. NOTE Annex B describes examples of different crevice formers and relevant aspects concerning these. Other different types of crevice formers can be used if relevant parties agree. 5.8 Test solution, commonly containing of chlorides. 5.9 Auxiliary electrode of high-purity platinum or other materials inert to the test solution. The auxiliary electrode may be constructed in the form of thin foil, a sheet, a rod, or in the form of a gauze. It can also be supported on a glass frame. The area of the auxiliary electrode shall be at least the area of the specimen. 5.10 Reference electrode shall be maintained at ambient temperature external to the test cell and connected to the test cell via a Luggin capillary probe. NOTE The silver/silver chloride electrode is preferred but there are other alternatives. The potentials of these Ag/AgCl electrodes at 25 °C relative to the standard hydrogen electrode at 25 °C are given in Annex D. 6 Procedure 6.1 Preparation of reference electrodes 6.1.1 The difference in potential between the reference electrode and two validation electrodes shall be measured. These electrodes shall be traceable to the standard hydrogen electrode and used and maintained solely for the purpose of validation. If the potential difference is greater than 3 mV, the test electrode shall be rejected.
6.1.2 The validation electrodes shall be stored in optimum conditions and regularly compared. Replacement shall be undertaken if the potential difference between these varies by more than 1 mV. 6.2 Preparation of specimen 6.2.1 The minimum specimen area of 1 cm 2 shall be used but the dimensions shall be compatible with the crevice former or the crevice holder used for the test. Examples of specimens are given in Annex A. 6.2.2 The surface finish shall be as reproducible as possible. Any test surface may be tested but it is recommendable that all surfaces exposed to the test solution, including cut edges and drilled holes, shall be abraded down to a surface finish of at least P 80grit paper. Care shall be taken to avoid overheating the surface. NOTE Ultrasonic cleaning can be used after the preparation. 6.2.3 The specimens shall be left in air, at a temperature higher than the dew point temperature for at least 24 h before testing, to be able to form a stable oxide. The time elapsed between grinding and immersion can have an influence on the subsequent crevice corrosion behaviour. The elapsed time selected will depend on the purpose of the test, but should be standardized for a particular set of tests. Little variation in surface film thickness occurs after 24 h, and hence a minimum elapsed time of 24 h is often useful.