1028 Development and Performance Prediction of Water Jet Peening (WJP) : (4) Residual Stress Prediction Based on Bubble Collapse Energy

We developed the new method for predicting a region of compressive residual stress on the weld surface after water jet peeing (WJP), which is a preventive maintenance technology for nuclear power plants. A cavitating jet is impinged on the weld surfaces of structures in a nuclear reactor. Bubble collapse impact causes plastic deformation of the weld surface, and changes the residual stress from tensile to compressive. Compressive residual stress prevents the occurrence of stress corrosion cracking (SCC) on the weld surface. A cavitating jet vertically injected into a submerged flat plate was investigated. Tensile stress was introduced onto the surface of the stainless steel plate by grinding before WJP in the experiment. We numerically simulated impulsive bubble pressure that varied by microseconds in the cavitating jet with the “bubble flow model”. The bubble flow model simulates the abrupt time-variations in the radius and inner pressure of bubbles based on the Rayleigh-Plesset equation in a cavitating flow. The cavitation collapse energy was estimated based on the bubble pressure. The cavitation collapse energy was compared with the measured compressive residual stress on the flat plate after WJP. The radial range of the compressive residual stress from the jet center axis is one of the most important measures of performance of WJP. The radial range of the cavitation collapse energy corresponded to that of compressive residual stress with a prediction error of +/− 20% under different conditions of jet velocity and the distance between the jet nozzle and plate surface. The results confirmed that the method we developed for predicting the region of compressive residual stress after WJP was valid.

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Mitigation of Stress Corrosion Cracking Based on Residual Stress Improvement by Water Jet Peening (WJP)

ASME 2011 Pressure Vessels and Piping Conference: Volume 1 ◽

10.1115/pvp2011-57493 ◽

2011 ◽

Cited By ~ 1

Author(s):

Masashi Fukaya ◽

Fujio Yoshikubo ◽

Hisamitsu Hatoh ◽

Yuji Matsui ◽

Yoshiaki Tamura ◽

...

Keyword(s):

Residual Stress ◽

Stress Corrosion ◽

Stress Corrosion Cracking ◽

Nuclear Power ◽

Water Jet ◽

Corrosion Cracking ◽

Bubble Collapse ◽

Bubble Pressure ◽

Stress Simulation ◽

Cavitating Jet

We have developed a practical peening technology using cavitating water jet. Water jet peening (WJP) is a preventive maintenance technology for nuclear power plants. WJP changes the residual stress on weld surfaces of reactor internals from tensile to compressive to mitigate the stress corrosion cracking (SCC). The operating conditions of WJP are controlled on the basis of ‘JSME Codes for Nuclear Power Generation Facilities.’ WJP has several advantages of operation, especially no foreign material is left in the reactor vessel since only water is injected, and wide range of the residual stress improvement is obtained since the cavitating flow spreads along the weld surface. We have also developed a prediction method of the residual stress improvement by WJP using a combination of a cavitating jet simulation and a residual stress simulation. We numerically simulated impulsive bubble pressure that varied in microseconds in the cavitating jet with ‘bubble flow model’. The bubble collapse energy was estimated by the bubble pressure. The residual stress simulation was conducted under the input conditions obtained from the bubble collapse energy. The residual stress distributions on and under the weld surface were predicted. The distributions were compared with measured data, and the result confirmed that the developed method for predicting the compressive residual stress after WJP was valid.

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1025 Development and Performance Prediction of Water Jet Peening (WJP) : (1) Principle and Application of WJP

The Proceedings of the Materials and Mechanics Conference ◽

10.1299/jsmemm.2010.1245 ◽

2010 ◽

Vol 2010 (0) ◽

pp. 1245-1247

Author(s):

Takahiro AOKI ◽

Kouichi KUROSAWA ◽

Fujio YOSHIKUBO ◽

Noboru SAITOU ◽

Tetsuya ISHIKAWA ◽

...

Keyword(s):

Performance Prediction ◽

Water Jet ◽

And Performance

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Improvement of Fatigue Strength by Using Cavitating Jet in Air

Elevated Temperature Design and Analysis, Nonlinear Analysis, and Plastic Components ◽

10.1115/pvp2004-2988 ◽

2004 ◽

Cited By ~ 1

Author(s):

Hitoshi Soyama ◽

Dan Macodiyo

Keyword(s):

Residual Stress ◽

Fatigue Strength ◽

High Speed ◽

Diffraction Method ◽

Water Jet ◽

Bubble Collapse ◽

Surface Residual Stress ◽

Hydraulic Machinery ◽

Rotating Bending Fatigue ◽

Cavitating Jet

Cavitation normally causes severe damage in hydraulic machinery such as pumps and valves. However, the cavitation impacts at the bubble collapse can be used to enhance the surface of metallic materials just as the same way as shot peening. In case of peening using cavitation impact, the cavitation is produced by injecting a high-speed water jet in a water-filled chamber. The authors have already demonstrated the fatigue strength improvement of materials using a high-speed water jet in water. Recently the authors succeeded in producing a cavitating jet in air by injecting a high-speed water jet into a low-speed water jet using a concentric nozzle. Cavitating jet in air can be used to peen parts of plant which cannot peened by the water-filled chamber, thereby impeding the initiation and/or the development of cracks. In this study, in order to demonstrate the improvement of fatigue strength of materials using cavitating jet in air, stainless steel (JIS SUS316L) was peened and the residual stress measured using the X-ray diffraction method. The surface residual stress of non-peened and peened specimen was −68 MPa and −350 MPa, respectively. The fatigue strength of the specimen were then investigated using the rotating bending fatigue test, with a stress ratio of R = −1. The fatigue strength of peened specimen by cavitating jet in air improved by 20% compared with nonpeened specimen.

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