Cavitation erosion

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Cavitation erosion is a phenomenon in hydraulic flow machines and the associated components of hydraulic systems , which are caused by strongly fluctuating pressure differences. They are the result of strong changes in the local velocities for the liquid. In areas with very high velocities, the pressure drop when the associated boiling temperature is exceeded and vapor bubbles form, which suddenly collapse again in areas with increasing pressure and below the boiling temperature. They are comparable to the pressure surges that can occur when steam is introduced into cold water.

These steam bubbles, called cavitation bubbles , lead to strong local pressure surges when they collapse. If this takes place in areas of material walls, damage to the metal surface can lead to cavitation erosion.
This type of erosion also occurs in a liquid without corrosive properties. Corrosive conditions in the liquid can, however, increase the damage.

causes

Cavitation is caused by the physical and structural conditions for the liquid. The trigger can be the following:

  • Increase in the local speed with a decrease in pressure up to the formation of vapor bubbles
  • Rise in pressure above the boiling point of the liquid with sudden collapse of the vapor bubbles

It can be reinforced by:

  • chemical reactions as a result of the action of oxygen at high pressure and - locally - high temperature
  • Element formation with electrolytic erosion in acidic or basic water.

Avoidance

As well as several causes trigger this erosion, there are also different measures to prevent it. This includes the following:

  • Decrease in temperature for the liquid
  • Increasing the pressure for the liquid
  • In the case of centrifugal pumps and system components: Reduction of the delivery rate and flow rate, as this leads to a reduction in the flow velocity and thus to a local pressure increase
  • Use of alloyed materials that are generally more resistant to erosion

literature

  • Winterthur Sulzer pumps (ed.): Centrifugal pump manual. 4th edition, Vulkan Verlag, Essen 1997, ISBN 3-8027-2176-4 .
  • Karl Sommer, Rudolf Heinz, Jörg Schöfer: Wear of metallic materials. Assessing forms of appearance reliably, Springer Vieweg Verlag, Wiesbaden 2012, ISBN 978-3-83482-463-9 .
  • Johann Friedrich Gülich: Centrifugal Pumps. Handbook for development - system planning and operation, 2nd edition, Springer Verlag, Berlin / Heidelberg 2004, ISBN 978-3-662-08218-8 .

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