• Corrosion Science and Technology
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• v.17 no.6
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• pp.310-316
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• 2018

The effect of passive film on corrosion of metals and alloys in a static corrosive environment has been studied by many researchers and is well known, however few studies have been conducted on the electrochemical measurement of metals and alloys during cavitation corrosion conditions, and there are no test standards for electrochemical measurements 'During cavitation' conditions. This study used commercially additive manufactured(AM) pure titanium in tests of anodic polarization, corrosion potential measurements, AC impedance measurements, and repassivation. Tests were performed in 3.5% NaCl solution under three conditions, 'No cavitation', 'After cavitation', and 'During cavitation' condition. When cavitation corrosion occurred, the passive current density was greatly increased, the corrosion potential largely lowered, and the passive film revealed a small polarization resistance. The current fluctuation by the passivation and repassivation phenomena was measured first, and this behavior was repeatedly generated at a very high speed. The electrochemical corrosion mechanism that occurred during cavitation corrosion was based on result of the electrochemical properties 'No cavitation', 'After cavitation', and 'During cavitation' conditions.

• Corrosion Science and Technology
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• v.20 no.6
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• pp.325-334
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• 2021

In the open system (vessel and pipe), the maximum corrosion rate of carbon steel at ca. 80 ℃ was obtained due to the decrease of dissolved oxygen by increasing the solution temperature. Effect of temperature on the cavitation damage can be explained through several mechanisms. Moreover, when cavitation occurs on the surface of metal and alloys, whether cavitation is erosion or corrosion is still controversial. This work focused on the effect of solution temperature on the corrosion of carbon steel under cavitation in an open system, Tests were performed using an electrochemical cavitation corrosion tester in 3.5% NaCl solution and the effect of solution temperature of carbon steel was discussed. Cavitation corrosion rate can be increased by cavitation, but when the temperature increases, a dissolved oxygen content reduces at a very high speed and thus the maximum cavitation corrosion temperature changed from 80 ℃ to 45 ℃. Below the maximum cavitation temperature, the electrochemical effect was more dominant than the mechanical effect by increasing temperature, but over the maximum cavitation temperature, the mechanical effect was more dominant than the electrochemical effect by increasing temperature.

• Corrosion Science and Technology
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• v.19 no.4
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• pp.163-173
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• 2020

Cavitation corrosion in many industrial plants has recently become a serious issue. Cavitation corrosion has generally been investigated using a vibratory method based on ASTM G32 standard, and the test can be divided into direct cavitation and indirect cavitation. Cavitation corrosion test uses the vibration frequency of the horn of 20 kHz with constant peak-to-peak displacement amplitude. In this work, the peak-to-peak amplitude was controlled from 15 ㎛ to 85 ㎛, and electrochemical measurements were obtained during indirect cavitation. The relationship between cavitation corrosion rate and electrochemical properties was discussed. Corrosion steps of carbon steel at the initial stage under cavitation condition in 3.5 % NaCl can be proposed. When the cavitation strength is relatively low, corrosion of the steel is more affected by the electrochemical process than by the mechanical process; but when the cavitation strength is relatively high, corrosion of the steel is affected more by the mechanical process than by the electrochemical process. This work confirmed that the critical ultrasonic amplitude of 0.42 %C carbon steel is 53.8 ㎛, and when the amplitude is less than 53.8 ㎛, the corrosion effect during the cavitation corrosion process is higher than the mechanical effect.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.36 no.2
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• pp.139-146
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• 2000

Cavitation can occur in pipes when liquid is moving at high velocity, especially at pittings where the smooth bore of the pipe is interrupted. The effect is usually to produce pitting on the downstream side of the turbulence. However, stress corrosion cracking behavior under cavitation erosion-corrosion was neatly unknown. In this study, therefore, some were investigated of stress corrosion cracking behavior, others were stress corrosion cracking behavior under cavitation erosion-corrosion of water injection. And datas obtained as the results of experiment were compared between the two. Mainresult obtained are as follows: 1) Stress corrosion cracking growth rate of heat affected zone under cavitation erosion-corrosion becomes most rapid, and stress intensity factor $K_1$becomes most high. 2) Stress corrosion cracking growth mechanism by cavitation erosion-corrosion is judgement on the strength of the film rupture model and the tunnel model. 3) The range of potential as passivation of heat affected zone is less noble than that of base metal, and that value is smaller. 4) Corrosion potential under cavitation erosion-corrosion in loaded stress is less noble than that of stress corrosion, and corrosion current density is higher.

• Corrosion Science and Technology
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• v.11 no.5
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• pp.184-190
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• 2012

Cu alloy is widely used for marine applications due to its excellent ductility and high resistance for corrosion as wells as cavitation. However, long term exposure of the material to marine environments may result in damages caused by cavitation and corrosion. Water cavitation peening has been introduced in order to improve resistance of Cu alloy to corrosion and cavitation. The technology induces compressive residual stress onto the surface, and thus enhances the fatigue strength and life. In this study, the characteristics of the material were investigated by using water cavitaiton peening technique, and results showed that 2 minutes of water cavitation peening indicated the considerable improvement in hardness. On the other hand, over 10 minutes of water cavitation peening accelerated damages to the surface. In the case of ALBC3, water cavitation peening in the range of 2 to 10 minutes has shown the excellent durability and corrosion resistance while minimizing surface damages.

• Corrosion Science and Technology
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• v.21 no.2
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• pp.138-146
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• 2022

The cavitation and potentiodynamic polarization experiments were conducted simultaneously to investigate the effect of cavitation amplitude on the super austenitic stainless steel (UNS N08367) electrochemical behavior in seawater. The results of the potentiodynamic polarization experiment under cavitation condition showed that the corrosion current density increased with cavitation amplitude increase. Above oxygen evolution potential, the current density in a static condition was the largest because the anodic dissolution reaction by intergranular corrosion was promoted. In the static condition, intergranular corrosion was mainly observed. However, damage caused by erosion was observed in the cavitation environment. The micro-jet generated by cavity collapse destroyed the corrosion product and promoted the repassivation. So, weight loss occurred the most in static conditions. After the experiment, wave patterns were formed on the surface due to the compressive residual stress caused by the impact pressure of the cavity. Surface hardness was improved by the water cavitation peening effect, and the hardness value was the highest at 30 ㎛ amplitude. UNS N08367 with excellent mechanical performance due to its high hardness showed that cavitation inhibited corrosion damage.

• Journal of Fisheries and Marine Sciences Education
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• v.10 no.2
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• pp.226-238
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• 1998

With the advent of high speed and high output diesel engines, cavitation erosion-corrosion of wet cylinder liners is one of the most prevalent types of failure. The cavitation erosion-corrosion at cylinder liners in water cooled diesel engines is considered to be to the collapse of cavitation bubbles attributed to the cylinder liner vibration. To suppress cavitation damage in cylinder liner, the addition of an inhibitor would be more general method and innovations such as the improvement in the geometric design of the equipment or the selection of suitably resistant construction materials are necessary. In this study, photomicrographs from vibratory facility cavitation specimens and from an eroded liner of a field diesel engine are compared. The behavior of cavitation bubbles grown in fluid is observed under vibration conditions by taking direct photographs with high speed camera. In order to determine the contributions of pure cavitation erosion and of pure corrosion to the total cavitation damage are be studied by following an experimental programme which includes three types of test: (1)pure cavitation erosion test, (2)pure corrosion test, and (1)cavitation erosion-corrosion test. Also cavitation damage under vibratory cavitation is reduced by using flow in tap water.

• Corrosion Science and Technology
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• v.10 no.6
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• pp.218-224
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• 2011

The fresh water and sea water in present ships is used as cooling water for marine engine. Therefore, corrosion damage in seawater system is frequently occurred. In particular, in the impeller of pump, the performance and material span due to the corrosion and cavitation erosion has adverse effects. Most of the pump impellers in vessels are used Cu-Al alloy. Cu-Al alloy which having the excellent mechanical properties and corrosion resistance is widely used in marine environments. However, despite the excellent characteristics, the periodic replacement parts due to the cavitation damage in seawater is vulnerable to economic viewpoint. In this study, Cu-Al alloy used with impeller for centrifugal pump were conducted various experiments to evaluate its characteristics in seawater and fresh water solutions. As an electrochemical result, the dynamic conditions that exposed to the cavitation environment presented high corrosion current density with collapse of the cavity compared with the static conditions. Cavitation test results, the weightloss and weightloss rate in fresh water are observed more than those of seawater.

• Corrosion Science and Technology
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• v.14 no.5
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• pp.239-246
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• 2015

Stainless steel is generally known to have characteristics of excellent corrosion resistance and durability, but in a marine environment it can suffer from localized corrosion due to the breakdown of passivity film due to chloride ion in seawater. Furthermore, the damage behaviors are sped up under a cavitation environment because of complex damage from electrochemical corrosion and cavitation-erosion. In this study the characteristics of electrochemical corrosion and cavitation erosion behavior were evaluated on 16.7Cr-10Ni-2Mo stainless steel under a cavitation environment in natural seawater. The electrochemical experiments have been conducted at both static conditions and dynamic conditions inducing cavitation with different current density parameters. The surface morphology and damage behaviors were compared after the experiment. After the cavitation test with time variables morphological examinations on damaged specimens were analyzed by using a scanning electron microscope and a 3D microscope. the galvanostatic experiment gave a cleaner surface morphology presented with less damage depth at high current density regions. It is due to the effect of water cavitation peening under the cavitation condition. In the cavitation experiment, with amplitude of $30{\mu}m$ and seawater temperature of $25^{\circ}C$, weight loss and cavitation-erosion damage depth were dramatically increased after 5 hours inducing cavitation.

• Corrosion Science and Technology
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• v.19 no.6
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• pp.318-325
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• 2020

Generally, Al alloys of 5000 and 6000 series show excellent weldability, workability, and specific strength, and are widely used in ship building. A combined experiment via cavitation erosion and corrosion damage involving 6061-T6 Al alloy was performed using potentiodynamic polarization under cavitation erosion (hybrid experiments) with amplitude (cavitation strength). The corrosion current density was approximately 52-fold higher at 30 μm than under static conditions, suggesting that the amplitude greatly affected the damage. The degree of damage increased with increasing cavitation amplitude. After the hybrid experiment, the corrosion rate was compared according to the weight loss and damage depth, and the relationship between the two values was expressed as alpha value. The alpha (α) values at amplitudes of 5 μm, 10 μm and 30 μm were 5.11, 12.81 and 8.74, respectively, suggesting that the α value at 10 μm was greater than at 5 μm, and indicating local corrosion damage. However, the α value at 30 μm was smaller than that of 10 μm, which is attributed to higher damage via uniform corrosion than damage induced by local corrosion.