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Research Papers: Offshore Technology

J. Offshore Mech. Arct. Eng. 2017;139(6):061301-061301-7. doi:10.1115/1.4036911.

Mechanical properties and corrosion resistance of UNS S32205 duplex stainless steel (DSS) welds obtained under the application of controlled magnetic fields were evaluated in the context of offshore pipelines and flowlines applications. Tensile tests, impact toughness, and hardness measurements were performed. Corrosion behavior was evaluated by linear polarization resistance (LPR) and potentiodynamic polarization curves (PCs) using a synthetic seawater solution at different temperatures. An improvement in tensile strength, impact toughness, and corrosion resistance was observed with the application of magnetic fields during welding. This effect is attributed to the refinement in the microstructure of the weld metal along with the suppression of detrimental intermetallic tertiary phases. Applying an axial magnetic field of 3 mT during DSS welding by the gas metal arc welding (GMAW) process is a potential technique for improving the performance of offshore pipeline welds and may be implemented in both, double-sided single pass and single-sided multipass butt joints.

Commentary by Dr. Valentin Fuster
J. Offshore Mech. Arct. Eng. 2017;139(6):061302-061302-8. doi:10.1115/1.4037065.

Umbilical is an important equipment in the subsea production to supply a connection between the floater and the subsea well. Analyzing strength and fatigue behaviors under bending is a key requirement to assure safety. An analytical model is proposed for predicting the bending behavior of a steel tube wounded helically around a frictionless cylinder. A full three-dimensional (3D) finite element (FE) model of an umbilical is developed by considering the frictions and contacts among its components. The numerical results of the bending stress of a steel tube were validated against that of the analytical model. The impacts of friction coefficients on the bending stress, contact pressure, and friction stress have been further investigated by the established FE model.

Commentary by Dr. Valentin Fuster

Research Papers: Polar and Arctic Engineering

J. Offshore Mech. Arct. Eng. 2017;139(6):061501-061501-9. doi:10.1115/1.4036478.

Sloping structures are widely used in ice-infested waters because of their ability to reduce ice loading by inducing a bending failure in ice sheets. From model test data, a significant velocity effect on the breaking load of ice sheets has been reported. In this paper, the ice–fluid interaction process is investigated by adopting the Euler–Bernoulli beam theory for the ice sheet and the potential theory for the underlying fluid domain. Accounting for the inertia effect of the ice sheet and the hydrodynamics of sea water beneath the ice sheet, the results demonstrate a velocity effect on the ice breaking loads in-plane deformation, which compare well with the available model test data. Moreover, our model formulation and implementation is such that the solutions for different ice velocities can be obtained rapidly from the reference solution, which facilitates the development of a real-time simulator. It is also shown that the velocity effect depends on the ice compressive strength and the angle of sloping structure.

Topics: Stress , Ice , Failure , Fluids
Commentary by Dr. Valentin Fuster

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