Stress distribution at the fillet of an internal flange

This paper deals with the determination of the stress distribution at the fillet of a ANSI B16.5 flanges attached internally to a hollow cylinder. A load parallel to the axis of the cylinder and of variable eccentricity acts on a bearing plate which rests on the flange. The strains are measured by means of electrical resistance wire strain gages.As monopiles constitute an overwhelming majority of foundation types used in the current offshore wind market, this work focusses on large ANSI welding neck flanges in the primary load path of a wind turbine foundation, such as those typically found at the base of turbine towers, or at monopile to transition piece connections. Finally, a summary of issues associated with flanges as well as bolted connections is provided, and insights are recommended on the direction to be followed to address these concerns.The number of bolts depends on the ANSI plate flanges radius and thickness, type of tool used, size of the bolts, and predicted loads on the structure. These bolts serve the purpose of exerting a clamping force to keep the joint together [20]. The employment of ANSI blind flanges connections for OWTs has considerably increased in the past decade owing to the failures and subsequent economic losses associated with grouted connections. In this study, the issues and opportunities associated with bolted flange connections have been thoroughly reviewed and discussed for application in the offshore wind industry.

Further studies in the offshore wind industry can enable the optimal use of ANSI threaded flanges connections in design, manufacturing, installation, operation, maintenance, and decommissioning phases.


Ring flange connections for tubular towers, like those for wind turbines or chimneys, are subjected to significant fatigue loading. Next to the bolts, the weld connecting the flange to the tower shell also needs to be checked against fatigue failure. The flange causes local bending moments in the shell, which increase the meridional stress, i. e. stress concentrations occur. In this paper, the influence of geometrical imperfections on such stress concentrations is quantified and the influence of flange geometry on resulting stress is investigated. Recommendations are given for flange dimensions and the design procedure.