A new ultrasonic peening instrument was developed for underwater treatment of welds and welded structures. The Ultrasonic Peening (UP) established itself as a promising process for fatigue life improvement of welded elements and structures. The beneficial effect of UP is obtained through relieving of harmful tensile residual stresses and introducing of compressive residual stresses into surface layers of materials, and through decreasing of stress concentration in weld toe zones and enhancement of mechanical properties of the surface layers of the materials.

In the design of the underwater UP instrument specially selected anti-corrosion materials are used. The underwater UP instrument can be used for treatment of welds at depths up to 30 meters or, if required, with certain modifications, even deeper. Acoustic pump principle is used in the originally developed system for water cooling of the transducer. The developed UP system allows for improvement treatments at four different power levels and is using replaceable working heads that come in various configurations with variable numbers of pins, depending on the application.

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