Cavitation Demystified

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• Cavitation Demystified

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Phase Diagram of Water
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Cavitation A Simple Process

• Cavitation is the formation and subsequent
  implosion of vapor bubbles in a fluid
• Caused by significant pressure gradients within
  process equipment
• Pressure gradients typically generated by high
  velocity flow around
• Valves throttling (partially closed valves)
• Vanes moving portions of pump impellers
• Protrusions pitot tubes, vortex shedders, etc.

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Pressure Gradient Formation

• Arrows indicate flow direction
• Fluid is compressed above vane creating a high
  pressure region
• Fluid is rarified below vane creating a low
  pressure region
• Behind this low pressure region is another high
  pressure region

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Impeller Cavitation Regions
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Typical Impeller Cavitation Pattern
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Cavitation Demonstration
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Microjetting

• Vapor bubbles do not implode symmetrically
• Because of pressure gradients, they tend to
  implode towards hard objects

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Microjetting High Speed Photograph

• Microjet has formed
• Vapor bubble is in the
• process of imploding
• towards the nearby hard
• surface
• Shockwaves generated by microjetting can be up to
  145,000,000 psi
• This pressure vastly exceeds the compressive
  strength of any metal alloy

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The Alternative to Rigid - Elastic

• Cavitation energy can be dissipated two ways
• Into a rigid metallic substrate
• Plastic deformation
• Ultimate compressive failure
• Into an elastic substrate
• Hooks Law
• We modified our Durable Abrasion Resistant
  Elastomer to better withstand cavitation

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Belzona 2141 (ACR-Fluid)

• Project sprung from a US Coast Guard request
• Products had to survive 16 hours in a high speed
  test
• At the time, the best product lasted 12 hours
• Second formulation Belzona submitted lasted 20
  hours
• Coast Guard currently in the process of coating
  all rudders with Belzona 2141 (ACR-Fluid) to
  resist the severe cavitation of their service

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Equipment
Hydro Runner at a small Canadian Power Plant
Problem
Mild cavitation was decreasing generating
efficiency
Solution
Runner was coated with Belzona 2141 (ACR-Fluid
Elastomer) to restore and maintain efficiency.
After 2 years it is still in perfect condition.
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Equipment
ITT 3480 Impeller
Problem
Severe cavitation was necessitating a full
rebuild every 3 months
Solution
Impeller received two coats of Belzona 1321
(Ceramic S-Metal) and a final coat of Belzona
2141 (ACR-Fluid Elastomer). Impeller now lasts
28 months between rebuilds!
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Questions?
Thank You Very Much