Fatigue life improvement of welded doubling plates by grinding and ultrasonic peening

Fatigue life assessment is important for all floating offshore structures, both not only related to the new building stage but also related to lifetime extensions. Fatigue cracking occurs normally due to uncertainties in estimated fatigue life and this is a well-known problem for floating structures. In this paper, the aim has been to look deeper into the effects of grinding and ultrasonic peening (UP) in order to improve the service life of structural connections. Fatigue testing of full-size fillet-welded doubling plates has been performed. The paper presents results from these tests including as-welded condition and ground and UP improved specimens. The paper also presents alternative S-N curves for improved details. The primary goal has been to assess the possibility for fatigue life improvement of fillet-welded doubling plates where fatigue cracking may initiate from the weld root. The information gained in this project is considered to be important for the offshore industry working with floating structures as well as for development of new fatigue assessment procedures and requirements in standardisation.