Ultrasonic peening treatment of attachments – Met Mast

The aim with this report is to describe the ultrasonic peening treatment of welded attachments carried out offshore on a Met Mast at elevation +45 m and above.
A description of the ultrasonic peening equipment, ultrasonic peening procedure and time requirement for the treatment are briefly presented in this report.
Based on previous fatigue test of UP treated welds we assess the potential fatigue life extension for the treated specimens.

IIW Fatigue Recommendations classification of this detail is FAT 71. Our conservative estimate is that the specimens could be classified as FAT 151 after UP treatment. These two FAT values are stress ranges expressed as Design Curves, mean value minus two standard deviations, at 2. 106 cycles.
Notwithstanding the considerable fatigue life extension achieved for ultrasonic peening treated welds, we propose a conservative 4 times life extension. This value would represent a conservative and realistic fatigue life extension for the current structure and for the weld attachments treated.

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