Enhancement of Marine Corrosion and Tribocorrosion Resistance of Offshore Mooring Chain Steel by Aluminizing Process

Abstract

The safety of mooring systems and accessories is one of the most critical issues in the structural integrity of floating oil/gas and renewable offshore structures. Mooring chains and accessories operate under dynamic conditions in harsh marine environments. They are subject to severe wear and corrosion between their links due to relative movement from waves, wind, and ocean currents that disrupt structural integrity. To cope with this problem, the pack-aluminizing process was applied on the R4 grade offshore mooring chain steel for 2 h at 850 °C to improve corrosion and wear-corrosion (tribocorrosion) resistance in 3.5% NaCl. The tribocorrosion behaviour of untreated and aluminized samples was investigated by a tribo-electrochemical setup that simultaneously allows for collecting the wear and corrosion data. Potentiodynamic and potentiostatic corrosion and tribocorrosion tests were carried out to understand corrosion kinetics. Optical, SEM, XRD and EDS analyses were performed to characterize the aluminide layer and surface morphologies before and after tribocorrosion investigations. In polarization scans under corrosion and tribocorrosion conditions, the current showed a significant activation stretch of several orders of magnitude, with minor potential changes in the anodic region. Due to the galvanic effects of sliding under natural electrochemical conditions, the untreated R4 alloy exhibited cathodic properties in the wear track, while the aluminium coating was out of the wear track due to its oxide-forming ability. At the cathodic potential, two hard Al2O3 materials under pure mechanical effects and third bodies emerging from cracks on the coating surface increase the friction coefficient (COF), while the oxide product film, which has a lubricating ability and pits which reduces the contact area, caused a decrease in COF at the high anodic potential. The study revealed that while the aluminide layer improved the corrosion and tribological character of R4 alloy, material loss from wear track increased due to micro fractures and cracks in the coating layer during sliding tribocorrosion conditions.

Subsea jumper damage detection based on fractal analysis and modal characteristics

“…However, extended exposure to ocean currents inevitably induces vortex-induced vibrations, resulting in stress concentration and fatigue damage, leading to crack formation [1]. In addition, the transportation of multiphase mixtures can subject subsea jumpers to cyclic stress due to the oscillations of gas and liquid plugs, potentially causing pipeline instability, decreased strength, and fatigue damage [2][3][4][5][6]. Therefore, monitoring and maintaining jumpers is crucial for the long-term safety and reliability of subsea oil and gas production systems.…”

Motion characteristics of vertically loaded anchor during drag embedment in layered clay

“…Therefore, the pullout capacity can reach more than 100 times its weight to meet the design requirement [3]. Since the drag embedding process determines the ultimate embedding depth, movement direction of the VLA and ultimate bearing capacity of the upper platform, the drag embedding process must be accurately simulated [4,5,6,7].…”