**4.5 Wear**

Now we have been informed about the remarkable effects of scouring particles on the heat transfer film coefficients at very low liquid velocities, low pumping power requirements and their potential to remove fouling, one might wonder what the consequences are of the scouring action of the particles with respect to wear and /or material loss of the heat exchanger tubes and the particles. After many years operating experiences we have come to the conclusion that only in case of the formation of a weak corrosion layer on tube and/or particle material, the scouring action of the particles may cause material loss due to the removal of this corrosion layer. For applications where corrosion of metal surfaces does not play a role, we present the following examples:

In a US plant, after one year of operation, the cleaning particles made of chopped stainless steel wire lost 2.5 % of weight. This is caused by the rounding-off effects of the sharp edged cylindrical particles. In the second year, being substantially rounded-off already during the first year of operation, the weight loss of the particles dropped to less than 0.5%. Because the smooth stainless steel tube wall is not subjected to metal loss as a result of rounding-off effects, the material loss of the tubes should be much less than 0.5% per year.

Similar experiences have been obtained in Japan with stainless steel tubes and particles. Again, after one year of operation a weight loss of approx. 2% was measured. In the second year, this weight loss was negligible. Fig. 8 shows the rounding-off effects of chopped stainless steel wire as a function of operating time. The loss of approx. 2% in the first year of operation as mentioned above can also be avoided by using particles which have already been rounded-off mechanically directly after their fabrication (chopping) process.
