Session: OAC-06-01 Continued Safe Operation of Existing Assets-1

Paper Number: 122087

122087 - Helical Pipe Inner Surface Peening Using Acoustic Cavitation 

In the past, several studies have demonstrated inner surface pipe peening with straight, extended pipes or holes. Recently, there has also been an industrial demand for peening the inner surfaces of helical exchange pipes in power plants that experience cyclic thermal stress. However, despite this industrial demand, none of the existing peening techniques, including shot peening, water jet peening, laser peening, etc., are suitable for inner surface peening. This is because it is not feasible to extensively insert peening devices into helical pipes to access and peen the deep inner surfaces. Consequently, due to the inaccessibility of the inner surfaces, peening for helical pipes has not been achieved or reported.

For the first time, we introduce a novel method that utilizes acoustic cavitation to peen the inner surfaces of long and narrow helical pipes. The method involves simply using static water supplied inside the pipe, eliminating the need for physical shots. In the setup for the operation, the acoustic probe tip, placed outside the pipe, is fixed to make slight contact with the static water inside the pipe. This excites the water, producing cavitation that generates shockwave impacts on the inner surface, thereby forming compressive residual stress. In this arrangement, the impact energy for the inner surface peening is supplied by the acoustic pressure wave. Thus, as the impact energy is acoustically provided, no physical insertion of the device into the pipe is necessary in contrast to existing peeing methods which would require the insertion. This approach shows promise in enabling internal peening for various inner surfaces, including the inner surface of helical pipes, which are extremely challenging to access.

In this presentation, we present a theoretical framework for achieving uniform peening and the operational methods required. We also demonstrate that a significant amount of compressive residual stress can be achieved through acoustic cavitation on the inner surface, as demonstrated in a proof-of-concept experiment. The spatial distribution of the residual stress data aligns well with the theoretical predictions. Furthermore, the experimental results suggest that the present method is effective regardless of pipe length and inner diameter, making it applicable for a wide range of helical pipes.

Presenting Author: Sunghwan Jung Dankook University

Presenting Author Biography: Sunghwan Jung received his B.S. degree in mechanical engineering from the University of Iowa, Iowa City, IA. He received his M.S. and Ph.D degrees in mechanical engineering from the Massachusetts Institute of Technology, Cambridge, MA, respectively. He is currently a Professor in Dankook University, Korea. His research interests include ultrasonic cavitation peening/cleaning, fracture mechanics, wafer spalling, and microfluidics.

Authors:

Sunghwan Jung Dankook University
Prabhu Murugesan Dankook Univ.
Hyungyil Lee Sogang University