Issue 35

A. Mehmanparast et alii, Frattura ed Integrità Strutturale, 35 (2016) 125-131; DOI: 10.3221/IGF-ESIS.35.15 125 Focussed on Crack Paths Welding sequence effects on residual stress distribution in offshore wind monopile structures Ali Mehmanparast, Oyewole Adedipe, Feargal Brennan Offshore Renewable Energy Centre, Cranfield University , , Amir Chahardehi Atkins Energy A BSTRACT . Residual stresses are often inevitably introduced into the material during the fabrication processes, such as welding, and are known to have significant effects on the subsequent fatigue crack growth behavior of welded structures. In this paper, the importance of welding sequence on residual stress distribution in engineering components has been reviewed. In addition, the findings available in the literature have been used to provide an accurate interpretation of the fatigue crack growth data on specimens extracted from the welded plates employed in offshore wind monopile structures. The results have been discussed in terms of the role of welding sequence in damage inspection and structural integrity assessment of offshore renewable energy structures. K EYWORDS . Welding sequence; Offshore wind monopole; Residual stress; Fatigue crack growth. I NTRODUCTION elding is a metal joining process which is widely used in manufacturing of full scale components used in industrial applications. During the welding process inhomogeneous plastic strains, caused by thermal cycles (i.e. localised heating and cooling), are introduced into the material which subsequently lead to formation of residual (locked-in) stresses in the welded components. The extent of residual stresses in weldments can be quantified using different techniques. The non-destructive methods which are commonly employed to measure residual stresses are X-ray diffraction, for thin plates, and Neutron diffraction, for relatively thick geometries. It has been shown and discussed in previous studies by other researchers that compressive and tensile residual stresses play an important role in the fatigue crack growth behavior of cracked geometries (e.g. [1, 2]). Therefore, an important issue to be investigated and accounted for in the remaining life assessment of engineering components subjected to cyclic loading conditions is the influence of residual stresses on the fatigue crack growth behavior of welded components. In order to assess the structural integrity of offshore renewable energy wind turbine structures, which are subjected to fatigue and corrosion damage during operation, fatigue crack growth (FCG) tests have been recently performed on fracture mechanics compact tension, C(T), specimens made of 355D steel which is the material commonly used in fabrication of offshore wind monopiles. C(T) specimens were extracted from typical monopile weldment sections, example of which is given in Fig. 1, with the notch tip located in the middle of the heat affected zone (HAZ) and tested W