5. Operating problems

5.1 Sheet metal corrosion

A series of incidents occurred on the first high-temperature cowpers shortly after commissioning: the sheet metal cracked. It took several years to confirm that these disorders were due to stress corrosion initiated in the weld seam areas by the presence of alkali nitrates. Heating the air to high temperature leads to the synthesis of NO _x , which combine with water and condense on the wall, forming alkali nitrates with the insulation.

Figure 3 shows the NO _x levels recorded as a function of temperature. Several palliatives have been proposed. For the cowpers to be built,...