Cavitation Erosion Testing

What is Cavitation?

Cavitation is a form of erosion caused by the implosion of gas bubbles on a surface resulting in damage and material loss. We use vibratory apparatus to simulate the formation and collapse of cavities in a test liquid. This enables us to study the nature and the progression of cavitation damage and to rank and compare between several materials.

We have the facilities and expertise to provide cavitation erosion testing in accordance with the ASTM G32 standard.

How do we test for cavitation resistance?

Testing is carried out according to the ASTM G32 Standard, “Test Method for Cavitation Erosion Using Vibratory Apparatus” in either pure or salt water. We can plot cumulative erosion vs exposure by periodically interrupting the test and measuring the mass loss for 8 to 12 hours. If the material density is known, we can convert to a mean depth of erosion to directly compare materials.

Cavitation erosion testing

3D texture mapping with Alicona

How we analyse the surface?

As well as testing materials, we can identify cavitation-related failure mechanisms and evaluate the level of damage present on working equipment, such as pumps and impellers. We use materials characterization techniques to analyse the damage.

Sample and Horn

The equipment uses a 20 kHz transducer with 16 mm diameter horn with a peak to peak amplitude of 50 microns. A sample size of 25 x 25 x 5 mm is inserted in to the test tank with deionized water at 25 C and a stand off distance set to 0.5 mm.
Hourly monitoring

The mass loss is monitored at hourly intervals. Images are also captured hourly to reveal the progression of damage, shown in the image for aluminium (top) and tungsten carbide (bottom).
Cumulative Erosion

According to ASTM G32, the erosion goes through several stages; incubation, acceleration, maximum rate and deceleration. If the density of the material under test is known, the mean depth of erosion can be calculated and the stages can be estimated.
Cavitation Performance
Optical microscopy

A more in depth study can reveal the stages of cavitation over time using characterization techniques. Often these include optical and scanning electron microscopy along with non contact profilometry.
Materials Characterization
Profilometry

Alicona infinite microscope provides 3D images of the damage caused by cavitation as well as a profile of the surface. Pictured is a tungsten carbide sample with the surface profile analysed at 1, 2, 4 and 8 hours.
Materials Characterization
Scanning electron microscopy

SEM images of the surface taken at various stages of the testing reveal the progression of the cavitation damage over time.
Materials Characterization
Scanning electron microscopy

Cross section through the material reveals the depth of the damage produced.
Materials Characterization