Therefore, for steel used in offshore platforms, it is not only

required to have high strength, sufficient toughness, excellent weldability and cold workability, as well as

strong corrosion resistance, but also the steel itself and its welded joints need to possess

extremely high fatigue resistance. Measures to enhance the reliability and resilience of welded structures in offshore platforms:

first, increase the proportion of high-strength and high-toughness steel grades and significantly raise the strength grade of the steel used. For example,

in jack-up drilling platforms, it accounts for about 60%, and in semi-submersible drilling platforms, about

95% [1]. Additionally, metal companies such as Japan's Nippon Steel, JFE, and Germany's Dillinger

have adopted high-strength steels with tensile strengths ranging from 360 to 980 MPa in offshore platform steel standards to adapt to extreme

environments in high latitudes [2]. Second, optimize the welding processes for steel and improve the steel's welding

performance. Regarding the types of steel used in domestic offshore platforms, take fixed

oil production platforms as an example [3]. Due to impact and dynamic loads,

high-strength steels of 400~700 MPa are typically used, and yield strength 420 MPa grade steel is now widely

employed. Although Q420 steel has high strength, during the welding process, it tends to produce

a large amount of hardened structures and cold or hot cracks, which severely affect the fatigue performance of welded joints,

and under the influence of non-steady-state environments, fatigue failure may occur, compromising the safety of the entire platform structure. Therefore,

research on the fatigue behavior of welded joints in offshore platforms holds significant practical engineering application value.