Sub-Zero Temperature Fatigue Strength of Butt-Welded Normal and High-Strength Steel Joints for Ships and Offshore Structures in Arctic Regions

Ships and offshore structures operating in Artic regions face specific challenges such as ice loads and seasonal low temperatures. In order to meet these extreme environmental requirements, the effect of temperature on material behaviour needs to be considered. It is well known that static material properties (yield strength, fracture toughness etc.) undergo significant changes with temperature. In recent studies, significantly higher fatigue strength was observed in welded joints in comparison to estimates based on international standards. Fatigue strength increased even for temperatures far below the allowed service temperature based on fracture toughness results; however, studies on fatigue strength of structural steel at sub-zero temperatures are scarce. Moreover, material selection for ships and offshore structures is usually based on empirical Charpy and fracture toughness relations at the design temperature, minus a safety margin. This study aims at introducing an S-N curve database for welded joints that can be used to verify the fatigue design approaches for ships and offshore structures subject to sub-zero temperatures. Therefore, the effect of temperature on the fatigue strength of butt-welded normal and high strength steel structures is analysed experimentally for sub-zero temperatures. For this purpose, fatigue test results of SAW and MAG welded joints for temperatures down to −50 °C are analysed and the potential for changes regarding material selection for ships and offshore structures are discussed.