Development of peening technique using recirculating shot accelerated by water jet

Abstract

The present paper demonstrates the development of a peening technique using recirculating shot accelerated by a water jet that can be used as a risk free treatment in power and chemical plants.Although it is important to increase the reliability of structural materials used in large scale structures, such as power and chemical plants, it is hazardous to treat these structures by general shot peening (SP) techniques because of the risk of sparks and dust explosions. In the present study, an SP technique using a water jet to accelerate shot has been developed, and the conditions under which it is used have been optimised in terms of nozzle geometry, standoff distance and amount of shot. In order to demonstrate the effect of SP, austenitic stainless steel Japan Industries Standards SUS316L was peened and evaluated in terms of its residual stress, fatigue strength and resistance to stress corrosion cracking. IntroductionIn large scale structures, such as power and chemical plants, it is necessary to ensure its long time operation by enhancing the fatigue strength and suppressing the stress corrosion cracking (SCC) in the materials from which the structure is made. Shot peening (SP), which utilises the impact generated by shot, can be applied to enhance the fatigue strength of mechanical components by introducing compressive residual stress on the surface layer. 1-6 In order to carry out this treatment while the plant is in its operating condition, there must be no risk from sparks and dust explosions generated by shot colliding. In the present paper, we describe an SP technique in which the recirculating shots are accelerated by a water jet.It is well known that the residual stress on the surface layer introduced by mechanical processing or heat treatment is one of the major factors that affects the fatigue strength and the resistance to SCC. 7-13 The SCC usually occurs when we have a material under tensile stress, including residual stress, in a corrosive environment. As it is difficult to improve a material's resistance to corrosion and reduce its exposure to the environment during operation, its resistance to tensile stress should be improved. This can be performed by introducing compressive residual stress on the surface for example using peening techniques, such as SP, cavitation peening 14-17 or laser peening. [18][19][20] In general, air blast systems and centrifugal blast systems are used for accelerating shot. The shots hit the surface in high velocity and broke due to colliding. 21,22 There is a possibility that sparks and dust explosions generate in such situation. 23,24 For this reason, general SP treatment is always exposed to risk of sparks and dust explosions. In order to avoid the risk of sparks and dust explosions caused by solid body collisions, it is essential to use a dust collector and a separator. As those systems make the SP apparatus larger, it becomes more difficult to treat some structures. Therefore, an alternative technique for accelerating shot to replace air blast systems or centrifugal ...

Comparison between Shot Peening, Cavitation Peening, and Laser Peening by Observation of Crack Initiation and Crack Growth in Stainless Steel

“…Shot peening was carried out using recirculating shot accelerated by a water jet system, which was developed by Naito et al [38], and was used by us in the previous study [17]. Figure 7 shows a schematic diagram of the shot peening system.…”

Increase of bending fatigue resistance for tungsten inert gas welded SS400 steel plates using friction stir processing

“…As mentioned in the introduction, to increase the fatigue strength of weld joints, various surface treatment techniques have been studied. The number of cycles to failure of the weld joints with surface treatments such as the laser peening [12] and the shot peening [13] significantly increased with decreasing applied stress amplitude or maximum applied stress. Although fatigue-test conditions such as a load ratio and tensile strengths of structural steel plates investigated are different, the significant increase of the number of cycles to failure was not observed in this study, but it was obtained by further refinement in the fine-grained FSP region (not shown here).…”

“…However, the FSP technique has not yet been applied to weld joints of steel plates for the purpose of optimizing the surface strength and fatigue performance. The fatigue strength of weld joints is much lower than that of the base metals, and thus various surface treatment techniques such as ultrasonic peening [7][8][9][10][11], laser peening [12], shot peening [13][14][15][16][17][18], and hammer peening [19,20], have been studied as means for improving fatigue strength of the weld joints. Although the application of FSW to steels and other high-temperature materials has been limited due to the absence of a suitable tool material, FSW of carbon steels has been reported by several groups [21][22][23][24].…”

Introduction of Compressive Residual Stress by Means of Cavitation Peening into a Titanium Alloy Rod Used for Spinal Implants

“…For this reason, there has been an attempt to enhance the reliability of the titanium alloy used for the spinal implant rod by use of peening techniques, which are known to introduce compressive residual stress into the surface layer [1]. The compressive residual stress enhances the resistance to fatigue [2][3][4], stress corrosion cracking [5] and hydrogen embrittlement [6][7][8]. Several practical peening techniques have been developed such as shot peening, which utilizes impact caused by collision between solid bodies, laser peening, which utilizes the impact caused by an ablative interaction and cavitation peening, which utilizes the impacts caused by the collapse of cavitation bubbles.…”