Avesta cell

Here distilled water instead of argon is pumped into the test cell at the crevice between the sample and the sample mounting. With a few exceptions, the Avesta cell is like the usual electrochemical cell for corrosion measurements (Figs. 14 and 15). The Avesta cell is made up of two concentric cylindrical glass pieces with a top and bottom made of polyvinylidene fluoride pieces. 

The electrolyte (the bulk solution) is in the inner of the two chambers, and thermostat fluid circulates in the outer chamber, hi the top of the Avesta cell are mounted the salt bridge from the reference electrode, a thermometer, nitrogen gas inlet, counter electrode, and perhaps a mechanical stirrer. 

Normally, square specimens are cut from 2-5-mm-thick sheet material. Two versions of the Avesta cell have been developed. One contains 120 ml of solution and uses specimens with an exposed area of 1 cm. The other contains 1200 ml of solution and uses specimens with an exposed area of 1-5-10 cm. The specimen is mounted as illustrated (Fig. 15). There is a small flow (0.1 ml/min) of distilled water through the pores of a ring of filter paper in the crevice between the specimen and the cell bottom. The filter paper ensures an even distribution of the flow of distilled water. In this way the liquid in the crevice is flushed constantly and the chloride ions do not enter the crevice and cannot initiate crevice corrosion. 

The Avesta cell was originally used for testing sheet material as shown here. However, with a few changes, tubes and welds can be tested as well without preparatory machining. ... 

Figure 15. Detail of the bottom of the Avesta cell. Crevice corrosion is avoided by a small flow of distilled water through the pores of filter paper at the crevice at the specimen/mounting interface. I. specimen. 2. O-ring. 3. Filter paper ring.

Figure 16. Electrode for pitting measurements with cylindrical specimens using the Avesta cell principle. The modification of the specimen holder is described in ASTM GS. Designed by Mathiesen and Maahn. (Reprinted from Ref. 73 by permission of the authors.)...

Specimen is in cylindrical form and together with its mounting is suspended in the solution. This specimen holder can easily be introduced in the Avesta cell by covering the hole in the bottom and by making slight changes in the top of the cell. 

In testing sheet, welded, and pipe material, the specimen is placed as a part of the bottom plate of the Avesta cell. Especially at higher temperatures there will be a difference between the temperature of the solution and the temperature of the specimen. This can be corrected for by calibration. When the modified ASTM G5 electrode holder is used, the specimen is totally immersed in the solution and no correction is needed. 

Summarizing, the Avesta cell is a flexible and convenient device for measuring pitting corrosion without interference from crevice corrosion. 

In 1989 Quarfort showed that the potential-independent CPT can be determined as a well-defined value ( 1°C). The Avesta cell (1 cm exposed area, 120 ml electrolyte volume) was used. 

Figure 35 Schematic diagram of the Avesta cell. Note that some details such as the thermometer have been omitted. (From Ref. 29.)...

O/] Arvig, P. O. and Davison, R. M., Measuring Corrosion Resistance of Stainless Steels Using the Avesta Cell — Experiences and New Apphcations, 12th International... 

Varjonen et al. [25] studied the pitting corrosion resistance of Type 316 stainless steel in white waters containing thiosulfate using an Avesta Cell, where the pitting breakdown could be studied without interference from crevice corrosion. Salonen et al. [26] and Laitinen et al. [27] used the contact electric resistance (CER) method to study the effect of thiosulfate on the films formed on Type 304 stainless steel. In the CER method, the resistance of the films formed on metal surfaces can be studied as a function of potential. Stable passive films have a high electrical resistance, whereas unstable (or absent) films have a low electrical resistance. 

To avoid problems with crevice corrosion at the electrode holder, an Avesta cell was used in investigations of the effect of post-weld cleaning on corrosion resistance of austenitic and duplex stainless steels in a simulated CIO2 liquor [11,83,84],... 

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