Cavitation Erosion
by
S. M. Ahmed
Wear & Corrosion
The progressive deterioration, due
to corrosion and wear, of metallic
surfaces in use in major industrial
plants ultimately leads to loss of
plant efficiency and at worst a
shutdown
Wear:
The loss of material surface due
to mechanical action
Corrosion:
The chemical or electrochemical
reaction between a material,
usually a metal, and its environment
that produces a deterioration
of the material and its properties.

Wear is the loss of material surface resulting
from mechanical interaction with another
surface, body or fluid, which moves to it.
Types of Wear
Adhesive
Abrasive
Cavitation
Erosion
Fatigue
Slurry
Corrosive
Cavitation
Cavitation In Marine Propeller
Bubbles in Hydrofoil
Models of Nucleation
Crevice model( it is inherent for
boiling)
Particles suspended in the liquid ( it is
inherent for cavitation(
.
Harmful Results From
Cavitation in Hydraulic
machinery






Deterioration of performance
Vibration and Shaft Deflection
Bearing Failure
Packing or Seal Leakage
Erosion
High Noise Levels
Applications of cavitation

Applications of cavitation span many
industrial sectors, from peening treatment,
through ultrasonic lithotripsy, sonochemistry,
ultrasonic cleaning and wastewater
treatment, to jet cutting.
Cavitation Erosion
Cavitation is defined by the ASTM standard
as the formation and subsequent collapse of
cavities or bubbles that contain vapor or
mixture of vapor and gas within a liquid.
Bubble Collapse

Liquid micojet

Shock wave
The mechanisms o f Cavitation erosion

Liquid- Jet impingement
A bubble in a liquid irradiated with ultrasound implodes
near a solid surface
‫االجهادات الناشئة فى المواد‬
‫الصلبة‬
Stresses induced
solid materiald in
due
to cavitation
Erosion
The formation
and collapse of
vapor
bubbles in the
vicinity of a
solid surface
‫تطبيق عملي‬
‫دراسة التآكل في مضخات الري في ج‪.‬م‪.‬ع‬
‫التكهف يحدث للمضخة نتيجة الحاالت اآلتية‪:‬‬
‫‪.1‬عدم وجود الضغط الكافى عند المدخل والسحب‬
‫‪.2‬هواء مسحوب نتيجة حالة اضطراب السائل‬
‫‪.3‬إعادة دوران السائل سواء فى مناطق السحب أو‬
‫التسليم‬
‫‪.4‬االهتزازات‬
Recirculation at the inlet and outlet of
the impeller
A complete failure for the vanes of the radial flow impeller
Damage of shrouds from vibration Cavitation
Cavitation damage of the impeller inlet vane
from inadequate net positive suction head
‫عمليات اإلصالح الضارة‬
‫األجهزة المعملية لدراسة التكهف‬
‫‪ -1‬جهااااااااااااااااا التكهاااااااااااااااا الهاااااااااااااااا ا‬
‫‪vibratory cavitation device‬‬
‫الاااااااااااااااااااااااااااااااا ا‬
‫‪ -2‬القاااااااااااااااااااااااااااااااا‬
‫‪Rotating disck‬‬
‫‪ -3‬نفااااااااااااااااااااااااااااااااااا التكهااااااااااااااااااااااااااااااااااا‬
‫‪Cavitation tunnel‬‬
Power
Amplifier
Experimental
work
Power
Supply
Transducer
Vibratory Horn
Stationary
Specimen
L: Separation
Distance
Water out
Temperature
Controller
Water in
Schematic view of test apparatus
Eroded surface pattern.
Water
5 wt % O/W
2 wt % O/W
10 wt % O/W
Power
Supply
Power Amplifier
Oscilloscope
Transducer
Horn tip
Frequency
Counter
Vibratory Horn
Beaker
L: Separation
Distance
Delay
Circuit
Mirror
Xenon
Flash Lamp
Micro
Pulser
Water out
Camera
Lens
Temperature
Controller
Water in
Cooling Bath
Fig. 1. Schematic diagram of the experimental set up.
Cavitation erosion has long
been recognized as one of the
major problems in the design
and operation of modern highspeed flow systems. Therefore,
an early detection tool is needed.
Wear particle analysis, based on particle
size, shape and surface examination, can
play an important role in the diagnosis of
machine wear
The objective of the present study is to
identify the size distribution and shape
characteristics of the erosion particles.
And clarify their morphology features for
the characteristic stages of the vibratory
erosion rate-time pattern.
Results and discussion
Time dependence of cavitation damage
12
3
2
1
4
5
MDPR, mm/min.
10
8
6
MDPR  10
4
(I)
(II)
Wl
 A T
(IV)
(III)
2
0
0
4
8
12
Time, min.
16
20
Mean depth of penetration rate (MDPR) versus time
Experimental work
steps
Area
Equivalent
diameter (d)
Perimeter (P)
Elongation ratio (EL)
roundness (P2/4πA)
Particle
morphological
features
Particle
morphological
features
Incubation period
(1)
(2)
(3)
(4)
(5)
50
100
150
200
250
300
350
400
50
A
B
100
150
200
C
A. SEM image of particle,
B. the same image of the particle after the
application of a noise reduction filter,
C. boundary of image
250
RN  P / 4 A
2
EL= log2 (major axis/minor
axis), or
EL= log2 (a/b)
a
d
Morphology study based
on the circle with the
same area as the particle
b
Morphology study based
on the Legendre ellipse
Elongation ratio (EL)
1.2
1
0.8
0.6
0.4
0.2
0
1
2
3
4
5
Elongation ratio (EL) of particles removed at points 1-5
Roundness Factor (P2/4A)
2.7
2.6
2.5
2.4
2.3
2.2
1
2
3
4
5
Roundness (RN) of particles removed at points 1-5
Frequency, %
(2)
(4)
(5)
(3)
Size, μm.
Size distribution of particles removed at
points 2-5
■ CONCLUSIONS:

The particles removed during the incubation
period have distinctive morphological features
that differed from that for the subsequent
periods. These features include the lamella
shape, folding, curving and one of the particle
surfaces was the virgin surface. However, the
particles removed during the last three periods
of erosion process have similar appearances.
They have irregular shape and are thicker than
that for the incubation period.

The observation of particles characteristics
during the incubation period can be used as a
successful tool to detect early the cavitation
erosion for the ductile materials.