LAUSR

We study the processes of thermal formation of carbonate scale on steel surface and the influence of ultrasound on the scale structure with the help of two different approaches to the introduction of ultrasonic energy into the zone of scale formation: through water and through the metal. It is shown that the transmission of ultrasonic energy through the metal makes it possible to form protective scale layers with better barrier properties. The scale layer on the steel surface formed in the mode of steam boiler with simultaneous ultrasonic treatment for 50 h is continuous, microcrystalline, and very dense. The sizes of crystals do not exceed 2–3 μm and the density of the layer reaches 2.55 g/cm3, which is close to the density of calcite mineral (2.71 g/cm3). At the same time, in the absence of ultrasound, it is equal to 1.7 g/cm3 with crystal sizes of 30–40 μm. It is shown that, for this layer, the rate of steel corrosion does not exceed the normative rate equal to 0.05 mm/yr and heat transfer from the metal to water is almost not disturbed by the high density and small thickness of the scale layer.