Deckschichtbildung auf verschiedenen Stahlarten unter den Bedingungen des Hochdruck-Wasser-Dampfkreislaufes in Kraftwerken

Scale formation on different types of steel under the conditions of high pressure water/steam circulation in power stations The protective layer formed on steel in hot water and steam has predominantly spinel structure and consists of two strata. One of them is below the original steel surface and is formed by topotactic growth, while the other is above the original metal surface and is formed by epitactic growth. Their composition depends from the diffusivity of the heavy metal ions present. The mobility of the individual ions is different and is considerably higher in ferritic than in austenitic steels. The epitactic layer is more porous and less resistant than the topotactic layer. The topography of the spinel surface plays an important role with respect to flow resistance; crater type pits may be formed in the surface according to a mechanism yet unknown.