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 Erosion Fatigue Corrosive Cavitation Slurry

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

داوملا due ىف ةئشانلا تاداهجلاا ةبلصلا Stresses induced solid materiald in to cavitation

لاكساب اجيم 1000 ــ 100

Erosion

The formation and collapse of vapor bubbles in the vicinity of a solid surface

يلمع قيبطت

ع .

م .

ج يف يرلا تاخضم يف لكآتلا ةسارد : ةيتلآا تلااحلا ةجيتن ةخضملل ثدحي فهكتلا بحسلاو لخدملا دنع وأ بحسلا قطانم ىفاكلا طغضلا دوجو مدع .1

لئاسلا بارطضا ةلاح ةجيتن بوحسم ءاوه .2

ىف ءاوس لئاسلا نارود ةداعإ .3

ميلستلا تازازتهلاا .4

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

ةراضلا حلاصلإا تايلمع

فهكتلا ةساردل ةيلمعملا ةزهجلأا

ا ااااااااااااااااهلا ااااااااااااااااهكتلا اااااااااااااااااهج 1 vibratory cavitation device ا اااااااااااااااااااااااااااااااالا ااااااااااااااااااااااااااااااااقلا 2 اااااااااااااااااااااااااااااااااااهكتلا Rotating disck اااااااااااااااااااااااااااااااااااف ن 3 Cavitation tunnel

Experimental work Power Amplifier Power Supply Transducer Vibratory Horn Stationary Specimen L: Separation Distance Water out Water in Temperature Controller Schematic view of test apparatus

Eroded surface pattern.

Water 2 wt % O/W 5 wt % O/W 10 wt % O/W

Power Supply Oscillo scope Frequency Counter Delay Circuit Micro Pulser Power Amplifier Horn tip Beaker Lens Xenon Flash Lamp Cooling Bath Transducer Fig. 1. Schematic diagram of the experimental set up.

Vibratory Horn L: Separation Temperature Controller

Cavitation erosion has long been recognized as one of the major problems in the design and operation of modern high speed 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.

12 10 8 1 Results and discussion Time dependence of cavitation damage 3 4 2 6 4 2 (I) (II)

MDPR

 10 

Wl A



T

(III) (IV) 0 0 4 8 12 Time, min.

16 20 Mean depth of penetration rate (MDPR) versus time 5

Experimental work steps Area Equivalent diameter (d) Perimeter (P) Elongation ratio (EL) roundness (P2/4 πA) Particle morphological features

Particle morphological features Incubation period (1)

(2) (3) (4)

(5)

50 100 150 200 250 300 350 400 50 100 150 200

A.

A B SEM image of particle, application of a noise reduction filter, C B.

the same image of the particle after the C.

boundary of image

250

RN



P

2 / 4 

A

d EL= log 2 (major axis/minor axis), or EL= log 2 (a/b) b a Morphology study based on the circle with the same area as the particle Morphology study based on the Legendre ellipse

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

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

(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.