Currently, the US and Europe are the centers for the design of semi-submersible rigs.The American company FRIEDE & GOLDMAN was founded in the 1950s. At present, over 100 mobile offshore drilling units and production platforms in the world are designed by this company, which mainly has two types of deepwater semi-submersible rig, F&GExD and MillenniumSA. F&GExD is the semi-submersible rig of the sixth generation and its operational depth can reach up to 3050m. MillenniumSA is semi-submersible rig of the fifth and half generation with an operational depth of 2400m.