Cavitation Erosion Rate Research Articles

A study on surface topography in cavitation erosion tests of AlSi10Mg

Cavitation erosion causes serious problems for hydraulic machinery. This study focuses on the influence of surface topography on the cavitation erosion rate of AlSi10Mg using an ASTM G134 test rig. Polishing, grinding, turning, and laser texturing are employed to finish the surfaces. The obtained cavitation erosion rates are presented, and the surface topography, cross-section, and surface parameters are analyzed. The results indicate that the laser textured surface demonstrates a higher cavitation erosion rate than other surfaces. Certain patterns on the surface affect the deforming behaviors at the acceleration period of cavitation erosion progresses. 3D surface parameters, Ssk and Sku, can be employed for predicting the time required for removing the original surface finishing marks.

Investigation on failure process and structural optimization of a high pressure letdown valve

Abstract High pressure letdown valve in direct coal liquefaction is used to adjust the flow rate of coal–oil slurry that enters into the downstream separator. Severe erosion–cavitation wear is found on the valve spool, seriously affecting the safety and reliability of unit. The majority of this paper investigates the failure process of valve spool and proposes a corresponding structural optimization via computational fluid dynamics (CFD) methodology. Three geometries of different failure states are selected as the computational domains in the numerical simulation. The Schneer–Sauer model, particle rebound-velocity model and erosion model are employed to calculate the cavitation phenomenon and erosion rates distribution. Experiments of flow rates and cavitation on valve model under different pressure drops are conducted to validate the accuracy of numerical approach. Results showed that the damage development of valve spool aggravates the erosion–cavitation wear. The maximum erosion rates are located on the top of spool head in all the three states. The erosion rates on spool arc surface are two orders of magnitude higher than that on parabolic surface. The decrease in radius of spool head reduces the intensities of erosion–cavitation wear. The numerical results are in agreement with actual failure morphologies of valve spool in different states.

Vibroacustical Method for Measuring the Effect of Cavitation Erosion

One of the most harmful effects of cavitation, with strong influence on the life of the hydraulic machines is the destruction caused by erosion Since its discovery, over 150 years ago, evaluating the degradation is achieved by mass of material removed by erosion in a given time, which in the case of rotors and blades of hydraulic machines and marine propeller blades are equivalent by amount of electrode consumption for filling the voids left by the removal of material. Laboratory research on cavitation, from the beginning until now, evaluates the intensity of cavitation erosion rate, defined as a mass of material removed by erosion at a certain time of attack.The purpose of this paper is to develop and validate a technique based on vibroacoustic signal analysis of corroded samples, and that through their natural frequencies deviations to emphasize mass loss.The experimental measurement of the vibroacustic response of corroded specimens is carried out by using a condenser microphone. The vibration responses, in free-free conditions of the specimens, are analyzed using algorithm based on Fast Fourier Transform (FFT). The results are compared with other indicators of cavitation corrosion, such as lost mass and mass loss rate.

Porosity effects of a Fe-based amorphous/nanocrystals coating prepared by a commercial high velocity oxy-fuel process on cavitation erosion behaviors

Coatings with different porosities were prepared by controlling high velocity oxy-fuel process parameters. Pores were distributed homogeneously along the thickness of the coatings. Cavitation erosion rate of the coating was obtained by a vibratory cavitation equipment following ASTM G32 standard. As porosity of the coating increases, the cavitation erosion rate increases. Significantly high cavitation erosion rate was obtained in the early stage of the test for the coating with high porosity. As cavitation erosion test proceeds, the cavitation erosion rate tends to decrease. Cracks initiated in the surface pore area propagate along powder boundaries and merge to pores near surface. Due to the cracks, large coating parts consisting of a bunch of powders with good bonding were detached from the coating increasing the cavitation erosion rate. Corrosion products were preferentially formed on the pore areas enhancing the cavitation erosion rate. Consequently, pores near coating surface significantly accelerate the cavitation erosion rate through mechanical as well as chemical manners.

Ultrasonic cavitation erosion of nodular cast iron with ferrite–pearlite microstructure

The cavitation erosion of ductile cast iron with ferrite–pearlite microstructure was analyzed based on ultrasonic experiments performed according to ASTM G32-2010 and the resistance was compared to the C45 steel with similar hardness. The microstructural observation of the surface for different exposure times to the ultrasonic cavitation reveals the fact that the process initiates at the nodular graphite–ferrite interface and is controlled by micro-galvanic activities and mechanical factors. The cavitation erosion resistance was evaluated based on the evolution of the mean depth erosion and the mean depth erosion rate as a function of the cavitation time. The cavitation erosion rate of the cast iron is up to 1.32 times higher than the one of the C 45 steel with similar hardness. This is explained by the occurrence of stress concentrators due to the expulsion of the graphite from the metallic matrix.

Cavitation erosion damage of scroll steel plates by high-speed gas working fluid

A steel plate is one of the critical components of a scroll expander system that can experience cavitation micro-pitting while in service. The content of the present paper consists of two distinct but interrelated parts. The first part aims to highlight that the use of computational fluid dynamics (CFD) simulations can constitute a potential tool for the prediction of cavitation erosion areas in scroll expander systems. For this purpose, a three-dimensional CFD, steady-state numerical simulation of the refrigerant working fluid is employed. Numerical results revealed the critical areas where cavitation bubbles are formed. These numerical critical areas are in direct qualitative agreement with the actual eroded regions by cavitation, which were found by microscopic observations across the steel plate on an after use, scroll expander system. The second part of the paper aims to further investigate the behaviour and the durability of the steel plate of the studied scroll expander system subjected to cavitation erosion by using an ultrasonic experimental test rig. Scanning electron microscopy and optical interferometer micrographs of the damaged surfaces were observed, showing the nature of the cavitation erosion mechanism and the morphological alterations of the steel plate samples. Experimental results are explained in terms of the cavitation erosion rates, roughness profile, accumulated strain energy, and hardness of the matrix. The experimental study can serve as a valuable input for future development of a CFD numerical model that predicts both cavitation bubbles formation as well as cavitation damage induced by the bubbles that implode on the steels plates.

Cavitation Erosion Research on the X3CrNi13-4 Stainless Steel

The paper presents ample researches on cavitation erosion of two charges of stainless steel type X3CrNi13-4 on a cavitation stand, through the stationary specimen method. The results of the experimental trials are highlighted in tables and in graphics regarding the reproduction of mass losses and the cavitation erosion rate according to time. The images of the microstructures before the cavitation test and the macrostructures after the cavitation test of the two charges of stainless steel type X3CrNi13-4 are also presented in this paper.

A Study on Cavitation Erosion Behavior of Different Metals in Biomass Fuel/Diesel Blend

The cavitation erosion behavior of different metals, such as pure copper (Cu), steel GCr15 (ASTM A295) and stainless steel 1Cr18Ni9Ti (ASTM A276 321), in the emulsified biomass fuel/diesel (10wt% biomass fuel in blend with diesel fuel) was investigated by using a magnetostrictive-induced cavitation vibratory apparatus. The morphology of surface was observed by optical microscope and scanning electron microscope, and the cavitation erosion rates of three metals were evaluated by mass loss method. The surface compositions after cavitation erosion were analyzed by energy-dispersive X-ray spectroscopy. The experimental results showed that the surface morphologies and elements of Cu and GCr15 were changed greatly before and after cavitation erosion in the emulsified biomass fuel/diesel blend, as contrast to 1Cr18Ni9Ti. The degree order of cavitation erosion among three metals was Cu, GCr15 and 1Cr18Ni9Ti, because that the anti-corrosion effect of 1Cr18Ni9Ti played a great role in the mass loss by cavitation erosion.

Effect of temperature on cavitation erosion of 9Cr steel in liquid metal

Research on cavitation erosion in liquid metals is very important to confirm the safety of fast breeder reactors and industrial machinery. However, researches on the cavitation erosion in liquid metal are few compared with the study in water. In this study, the effect of the temperature on cavitation erosion in liquid metals is clarified. A cavitation erosion apparatus was developed to carry out erosion tests at high temperatures in liquid metals, and it was confirmed to offer a stable test performance. The test liquid was a lead–bismuth alloy and the specimens were made of 9Cr and SUS304 steels. The results showed that the cavitation erosion rate increased with increased temperature and reached a peak value at a relative temperature of about 70° (the relative temperature was defined as 0° for the freezing temperature and 100° for the boiling temperature). The erosion rate prediction was discussed for sodium. The erosion rate in sodium was estimated to be located halfway from the rates between lead bismuth and deionized water.

Influence of Surface Hardening Depth on the Cavitation Erosion Resistance of a Low Alloy Steel

Abstract In this paper, the influence of surface hardening depth promoted by plasma nitriding and Cr–Al–N coating deposition on the cavitation erosion resistance of a low alloy steel was investigated. Samples that were plasma nitrided for 2 and 4 h were produced and coated with 1 and 2 μm Cr–Al–N coatings deposited by plasma assisted physical vapor deposition. The characterization was carried out by X-ray diffraction (θ–2θ and glancing angle configurations), scanning electron microscopy, Rockwell C adhesion test, and three dimensional (3D) profilometry. Knoop microhardness tests were also performed. Cavitation erosion tests were carried out according to ASTM G32-03 Standard. The incubation period and cavitation erosion rate were determined. Coating deposition had a major influence on the incubation period, with thicker coatings resulting in longer times. Plasma nitriding treatment was more effective on reducing the average erosion rate. The plasma nitriding treatment and Cr–Al–N coating deposition in conjunction led to a decrease in both incubation period and erosion rate. The hardened systems presented mass loss up to 11 times lower than the nonhardened steel for the same time. It was concluded that the surface hardening was effective to improve the cavitation erosion resistance of a low alloy steel and the wear rate decreased with the increase of the hardening depth.

Experimental comparison of cavitation erosion rates of different steels used in hydraulic turbines

The prediction of cavitation erosion rates has an important role in order to evaluate the exact life of components in fluid machineries. Hydro-Québec has studied this phenomenon for several years, in particular in hydraulic turbine runners, to try to understand the different degradation mechanisms related to this phenomenon. This paper presents part of this work. In this study, we carried out experimental erosion tests to compare different steels used in actual hydraulic turbine runners (carbon steels, austenitic and martensitic stainless steels) to high strength steels in terms of cavitation erosion resistance. The results for these different classes of steels are presented. The tests have been performed in a cavitating liquid jet apparatus according to the ASTM G134-95 standard to simulate the flow conditions. The mass loss has been followed during the exposure time. The maximum depth of erosion, the mean depth of erosion, and the mean depth erosion rate are determined. As a result we found that ASTM-A514 high strength steels present excellent cavitation erosion resistance properties. The cavitation eroded surface is followed by optical profilometry technique. Determination of mechanical properties and examinations of the eroded surfaces of the samples have also been carried out in order to identify the erosion mechanisms involved in the degradation of these kinds of materials.

Prediction method for cavitation erosion based on measurement of bubble collapse impact loads

The prediction of cavitation erosion rates is important in order to evaluate the approximate life of components in fluid machinery. The measurement of impact loads in bubble collapses helps us to predict the life under cavitation erosion. In this study, we carried out the erosion tests and measured impact loads in bubble collapses with a cavitating liquid jet apparatus which complies with the ASTM G134-95 standard. The bubble collapse impact loads were measured by a piezo ceramic transducer in a cavitating liquid jet apparatus. To produce various cavitation conditions, the flow velocity was changed from 184 down to 80 m/s. We evaluated the incubation period based on a cumulative damage rule by measuring the impact loads of cavitation acting on the specimen surface and using the “constant impact load – number of impact curve” similar to the modified Miner's rule which is employed for fatigue life prediction. We found that the parameter ∑(Fiα×ni) (Fi: impact load, ni: number of impacts and α: constant) is suitable for the evaluation of the erosion life. After the constant α has been obtained under two different cavitation conditions, we can predict the incubation period with the cavitating liquid jet method under yet another condition, provided that the bubble collapse impact loads are measured.

Comparison of cavitation erosion rate with liquid impingement erosion rate

Both cavitation erosion and liquid impingement erosion are phenomena that can cause pipe wall thinning in power plants. The Code for Power Generation Facilities, Rules on Pipe Wall Thinning Management, was published by the JSME (Japan Society of Mechanical Engineers) in 2005. The code says that cavitation erosion shall be prevented either in the design stage or by daily inspection. On the other hand, liquid impingement erosion can occur in any location where a working fluid attacks a pipe wall at high flow velocities. Therefore, it is very important to evaluate the amount of erosion by liquid impingement for pipe steels quantitatively from the viewpoint of aging management. In this study, we carried out cavitation erosion and liquid impingement erosion tests, and clarified the relation between both erosion rates. As a result, we found that the erosion rate by cavitation increases in proportion with the 5.2nd to 6.8th power of the flow velocity and that by liquid impingement with the 6.0th to 7.4th power. Moreover, a good correlation was obtained between erosion rates by cavitation and by liquid impingement. We also discuss the erosion mechanism with SEM photography, and propose an erosion model.

Post-irradiation examination of the Spallation Neutron Source target module

The Spallation Neutron Source (SNS) at Oak Ridge National Laboratory is an accelerator-based pulsed neutron source that produces high-energy spallation neutrons by bombarding liquid mercury flowing through a stainless steel target vessel. During operation the proton beam and spallation neutrons produce radiation damage in the AISI 316L austenitic stainless steel target vessel and water-cooled shroud. The beam pulses also cause rapid heating of the liquid mercury, which may produce cavitation erosion damage on the inner surface of the target vessel. The cavitation erosion rate is thought to be highly sensitive to beam power and predicted to be the primary life-limiting factor of the target module. Though cavitation erosion and radiation damage to the target vessel are expected to dictate its lifetime, the effects of radiation damage and cavitation erosion to target vessels in liquid metal spallation systems are not well known. Therefore preparations are being undertaken to perform post-irradiation examination (PIE) of the liquid mercury target vessel and water-cooled shroud after end-of-life occurs. An overview of the planned PIE for the SNS target vessel is presented here, including proposed techniques for specimen acquisition and subsequent material properties characterization.

Prediction method for cavitation erosion based on measurement of bubble collapse impact loads

The prediction of cavitation erosion rates is important in order to evaluate the exact life of components. The measurement of impact loads in bubble collapses helps to predict the life under cavitation erosion. In this study, we carried out erosion tests and the measurements of impact loads in bubble collapses with a vibratory apparatus. We evaluated the incubation period based on a cumulative damage rule by measuring the impact loads of cavitation acting on the specimen surface and by using the "constant impact load - number of impact loads curve" similar to the modified Miner's rule which is employed for fatigue life prediction. We found that the parameter Σ(Fiα×ni) (Fi: impact load, ni: number of impacts and α: constant) is suitable for the evaluation of the erosion life. Moreover, we propose a new method that can predict the incubation period under various cavitation conditions.

Incubation Time and Cavitation Erosion Rate of Work-Hardening Materials

A phenomenological analysis of the cavitation erosion process of ductile materials is proposed. On the material side, the main parameters are the thickness of the hardened layer together with the conventional yield strength and ultimate strength. On the fluid side, the erosive potential of the cavitating flow is described in a simplified way using three integral parameters: rate, mean amplitude, and mean size of hydrodynamic impact loads. Explicit equations are derived for the computation of the incubation time and the steady-state erosion rate. They point out two characteristic scales. The time scale, which is relevant to the erosion phenomenon, is the covering time—the time necessary for the impacts to cover the material surface—whereas the pertinent length scale for ductile materials is the thickness of the hardened layer. The incubation time is proportional to the covering time with a multiplicative factor, which strongly depends on flow aggressiveness in terms of the mean amplitude of impact loads. As for the erosion rate under steady-state conditions, it is scaled by the ratio of the thickness of hardened layers to the covering time with an additional dependence on flow aggressiveness, too. The approach is supported by erosion tests conducted in a cavitation tunnel at a velocity of 65 m/s on stainless steel 316 L. Flow aggressiveness is inferred from pitting tests. The same model of material response that was used for mass loss prediction is applied to derive the original hydrodynamic impact loads due to bubble collapses from the geometric features of the pits. Long duration tests are performed in order to determine experimentally the incubation time and the mean depth of penetration rate and to validate the theoretical approach.

耐キャビテーション壊食性を有する高機能溶射皮膜の開発

Anti-cavitation erosion performances of thermally sprayed cobalt-based alloy coatings were compared with that of aluminum bronze castings, which have been utilized as s substrate for propeller in marine vessel because of its formability, endurance against seawater, and the cavitation erosion resistance. Cobalt-based alloy coatings are fabricated by using three thermal spray processes: atmospheric plasma spray, low-pressure plasma spray and high velocity oxygen fuel flame spray. The ultrasonic vibration type cavitation erosion testing apparatus were employed for the cavitation erosion rate measurement. The cavitation erosion performances determined by the specific volume loss rate of low-pressure plasma-sprayed cobalt-based alloy and HVOF sprayed cobalt-based alloy coatings were improved five times and twice compared with that of aluminum bronze castings, respectively. The anti-cavitation erosion performance of atmospheric plasma sprayed cobalt-based alloy coating did not reach the level of aluminum bronze castings.

Characterizing cavitation erosion particles by analysis of SEM images

Wear particles produced by vibratory cavitation erosion on stationary-aluminum Al-99.999 were analyzed using scanning electron microscope (SEM), forming a database for further analysis. The particle morphology features were first clarified based on the characteristic stages of the vibratory erosion rate-time pattern. Next, size, area, perimeter and shape factors (elongation and roundness) were determined for eroded particles, using image analysis software. In incubation period, the particles have distinctive characteristics which differed from that for the subsequent periods. These characteristics include the value of longitudinal ratio and roundness factor, limit size range and morphological features such as lamella shape, folding, curving with one of the particle surfaces as the virgin surface. In acceleration, steady-state and attenuation periods, the particles have a wide size range and larger thickness compared with that for the incubation period. The maximum particle size reached about 360 μm in acceleration and steady-state period. For all the cavitation erosion rate periods, the particles were out of sphericity and they have a roundness factor larger than 2. Detailed surface characteristics of the particles produced during cavitation erosion is significant and can open ways for monitoring the cavitation erosion progress.

Prediction of cavitation erosion on stainless steel components in centrifugal pumps

The Research Committee on Cavitation Erosion in the Turbomachinery Society of Japan has already reported the prediction method of cavitation erosion rate. However, the scattering between the predicted rate and the measured rate is 100 times. In this study, we compare fundamental data of stainless steels collected by the Committee with the data obtained in our laboratory. The influence of material and liquid parameters on the scattering of the Committee data is discussed. We found that the scattering was influenced by high liquid temperature, the kind of liquids, the microstructure of components and the operating life. We propose a modified prediction equation including these parameters, and found that the equation improve the accuracy of the erosion prediction.

Cavitation damage experiments for mercury spallation targets at the LANSCE – WNR in 2005

In-beam experiments investigating cavitation damage in short pulse mercury spallation targets were performed at the Los Alamos Neutron Science Center – Weapons Neutron Research (LANSCE – WNR) facility in 2005. Two main areas were investigated. First, damage dependence on three mercury conditions – stagnant, flowing, and flowing with bubble injection – was investigated by employing a small mercury target loop with replaceable damage test specimens. One hundred beam pulses were passed through the loop mercury and specimen pair for each test condition. Damage with flowing mercury ( V = 0.4 m/s) was less than half that which was incurred with stagnant mercury. Gas bubble injection added into the flow further reduced damage to about one-fourth that of stagnant mercury. Acoustic emissions from cavitation bubble collapse were concurrently measured on the exterior of the loop using a laser Doppler vibrometer and were correlated to the observed damage. The second area of experimentation was erosion rate dependence on proton beam intensity. Prior research had indicated that incubation-phase cavitation erosion rate is strongly dependent on beam intensity, by a power law with the exponent perhaps as large as 4. The 2005 results are inconsistent with earlier in-beam test results and do not support the power law dependence. This paper will provide a detailed description of the experiment, present results and discuss the findings.