Ultrasonic peening against fatigue cracking
Ultrasonic Peening is a post weld treatment which increases the resistance against fatigue cracking. If the treatment is applied when 50% of the fatigue life of a weld connection has been consumed, the fatigue life of this weld will be reset to zero. Likewise any weld with irregularities or uneven quality would be restored to an acceptable level by ultrasonic peening treatment. The treatment combines the benefit of the removal of crack-like flaws, weld-toe geometric modification and the redistribution weld induced tensile residual stresses at the HAZ.
Ultrasonic peening and weld defects
The notorious acceptance of ultrasonic peening as the preferred fatigue life extension method to be applied in-situ is due to the fact it performs three different improvements during one single working operation. The removal of weld defects, the lowering of stress concentrations and the redistribution of tensile stresses and/or introduction of compressive stresses are all issues that are performed during the ultrasonic peening treatment.
Ultrasonic peening and compressive stresses
The treatment is done by hammering the steel surface at a very high frequency, 20 kH, with a hardened steel peen. Due to the high intensity of the oscillation, the steel peen creates a smooth transition between plate and weld, called weld toe groove. Because the amplitude of the oscillating peen is so small yet powerful, a compressive layer at the treated surface is created. This layer increases the weld-toe resistance against fatigue cracks.
Ultrasonic peening procedure
The LETS Global Ultrasonic Peening Procedure can also be used on steel surfaces, without welded attachments. In these cases the surface treatment is carried out to create a compressive layer that strengthens the area against fatigue.
LETS Global specializes in the application of Ultrasonic Peening treatment on offshore installations and we can perform the treatment even in areas of difficult access.
The benefit of the LETS Global Ultrasonic Peening procedure has been demonstrated through its application on several offshore installations and in numerous research reports presenting fatigue test results. Further information including research published material can be found in the following link published papers.