The Study of corrosion fracture in marine risers

In order to convey the hydrocarbon to the sea level and do drilling operation, a steal pipe is installed between wellhead in the seabed and drill ships. The fluid dynamic forces are expressed in Morison formula using short wave theory. It is assumed that the riser is connected to the platform by means of a heave compensator. This device provides a large static tensile force at the top of the riser. Also it reduces the longitudinal stress variation induced by the relative vertical motion of the drill ship and the riser. With these assumptions the equations of motion governing the transverse displacement of the riser in two directions, in line and cross flow, can be obtained. At the end the effects of the corrosive environment on the crack propagation and fatigue life is investigated. For this study the experimental results of H2S and seawater effects on crack propagation in steels is used.So effect of initial crack in riser cross sections in different depths and at present of corrosive fluid is studied. At the end the effect of seawater and crude oil on crack propagation and corrosion fracture life is investigated. In order to solve riser dynamic equilibrium equations, Range-Kutta and finite difference methods have been used.