For the rational design, construction and operation of these offshore oil and gas facilities, as well as for ensuring the safety of maintenance personnel, studies of external impacts on the elements of such marine-structures are of particular importance. Depending on the design features of the operating conditions of stationary offshore platforms, their components experience local stability from loads caused by hydrostatic and external influences. Accounting for these effects is justified in each case. All structures of offshore fixed platforms, without exception, experience local action from sea waves and currents; for deep-sea stationary platforms, wave pressure on the lower sections can be neglected, but pressure from the current must be taken into account. As for the effect of hydrostatic pressure, it occurs for the structures of stationary platforms, which are made of sealed pipes to use their buoyancy during transportation and installation of the structure at sea, as well as to reduce the installation weight. In the practice of construction and operation of these types of structures, cases of loss of local stability were observed, i.e. due to the high hydrostatic pressure, individual elements were severely deformed, and some were even flattened. To guarantee stability in these elements, it is necessary to determine the critical maximum transverse load at which the local stability of the element will be ensured. It should be noted that, in addition to the transverse load, the element is also subjected to a longitudinal force, which is determined from the design scheme of the structure. With this formulation of the problem, it is necessary to consider the combined effect of the longitudinal force and the transverse load. The structural element is considered a shell of medium length.