The 70Cu–30Ni alloy has excellent resistance to seawater corrosion, but corrosion perforation still occurs during use for various reasons. Copper can suffer severe ammonia corrosion in NH4+ containing solutions and copper alloys are susceptible to stress corrosion in ammonia environments. Therefore, the effect of NH4+ and stress on the corrosion of 70Cu–30Ni alloy in seawater cannot be ignored. The main objective of this study was to investigate the accelerating effect of NH4+ and stress on the pitting of 70Cu–30Ni alloy. The effect of NH4+ and stress on the pitting of 70Cu–30Ni alloy in seawater was investigated using laser confocal scanning microscopy (LCSM), electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The results show that in seawater with NH4+ the depth and diameter of the pits and the number of pits in the specimens increase. NH4+ destroys the oxide film on the surface of the 70Cu–30Ni alloy and inhibits the repair process of the oxide film on the surface of the alloy, thus reducing the amount of protective Cu2O and NiO in the corrosion products of the specimen. In seawater with NH4+, the film capacitance CPEf and dispersion coefficient of the 70Cu–30Ni alloy interface are significantly lower, the oxide film is thinner and there are more local defects and poor protection. After loading stress, the pitting depth of the specimen increases further, showing stress corrosion cracking. Stress and NH4+ have a synergistic effect on the pitting corrosion of the alloy.
Sand erosion is a common problem in oil and gas field development. An experimental facility was designed and used to study the sand erosion of pipe bend under slug flow. A detachable test pipe bend was designed to measure the weight loss at 36 discrete locations on the pipe bend before and after each experiment. A Computational Fluid Dynamics (CFD) based erosion prediction method was developed to get a further understanding of the erosion. The relationships among the gas and liquid distribution, the sand movement and the erosion profile were analyzed to explain the erosion mechanism. The most severe erosion area of the pipe bend occurs at the axial angle of the elbow between 67.5° and 90° and at the circumferential angle of the elbow between 45° and 90°. The erosion profiles of the pipe wall are dominated by three particle collision mechanisms, namely, micro-cutting, plowing and impact deformation.
This work reports a silicone coating (PDMS-Ula) with marine antifouling and self-healing properties, which was prepared by the first synthesis of polydimethylsiloxane polymer containing imine and urea groups and then adding a small amount of eco-friendly antifoulant. The characteristic structure of the polymer was verified via Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (NMR). The PDMS-Ula coating has rapid self-repairing performance, excellent transparency and the ability to control the release of antifouling agents at a certain rate. The adhesion experiment using four typical benthic diatoms indicated that the PDMS-Ula coating can effectively inhibit the attachment of diatoms, which effectively improves the static antifouling ability of silicone materials. (C) 2020 Published by Elsevier B.V.
Organic coating effectively protects metal from corrosion in atmospheric environment. As the coating undergoes degradation in harsh environment enriched with Cl− and at high temperature, there is a need to develop in-situ electrochemical methods to in-field detect the defect size in organic coatings that exposed to atmospheric conditions. This work aims to develop several electrochemical methods including open circuit potential (OCP), electrochemical current noise (ECN), electrochemical impedance spectroscopy (EIS), galvanostatic step and potentiostatic step, and the parameters obtained from each method are compared. Experimental results indicate that, apart from corrosion potential, the other four techniques can effectively detect the defect size in organic coatings by using polarization resistance or charge transfer resistance. Galvanostatic step and potentiostatic step can be used in field corrosion detection due to its concise instrumentation and short measurement time.
During the development of oil and gas fields, it is common for elbow suffering from sand wear. In this study, the erosion performance of 316 L stainless steel at the elbow was analyzed using the slug flow erosion experiment loop. The experiment was conducted under slug flow with different superficial air and water velocities using a detachable elbow. After weighing the mass loss and analyzing the sample surface, the erosion rates in different parts of the elbow were quantified and the erosion regularity was analyzed. The results indicate that the increase in superficial air velocity has a greater impact on the erosion rate than that in the superficial water velocity. The maximum erosion damage occurs at the outer wall in the 67.5 degrees position. With the increase in superficial air and water velocity, the number of scratches on the maximum erosion position reduces. (C) 2020 Elsevier B.V. All rights reserved.
