The effects of fluid flow on the corrosion rate of pipes and tubes were studied with rotating disk electrode and a prediction method for corrosion rate was proposed. Polarization curves in both N2-purged and CO2-saturated NaCl solution were depolarized with the increase of angular velocity showing the increase of limiting current density and corrosion current density. The limiting current density increased linearly as a function of the square root of angular velocity which shows the rate determining process is the diffusion of H+ ion to the electrode surface. Another possibility contributing the rate determining process is the CO2 hydration reaction to H2CO3. The corrosion current density also increased as a function of square root of rotating velocity following the theoretical solution. Using the similarity solutions obtained for mass transfer with pipe flow and rotating disk electrode, the rotating velocity was converted to the equivalent velocity in pipe. On that basis the corrosion rate of pipe was equal to the corrosion rate of the rotating disk electrode. The corrosion rate of rotating disk electrode obtained by the electrochemical method was used to predict the corrosion rate of the pipe at the equivalent velocity.
Erosion-corrosion behavior was studied under various gas-liquid ratios in two phase flow of steam and hot water at the maximum flow velocity of 246m/s. Obtained results were compared with the results in Onikobe geothermal brine. Corrosion rates of mild steels increased gradually with gas-liquid ratio in soft waters of pH=2, 9.6 and in Onikobe geothermal brine. Corrosion rates of stainless steels were constant in the laboratory test and the field test, even if the ratio changed.
Generally, corrosion rate for steel and cast iron in seawater increases with an increase of the flow rate. On the contrary, in cases where there is a flow rate distribution inside of the pump casing for example, the low flow rate area is sometimes prefferentialy corrodes owing to differential aeration cell caused by a differential flow rate. This study examined the mechanism of the differential aeration cell corrosion owing to the differential flow rate for cast iron in seawater through experiments and numerical analysis. The measurements have been performed on the potential, polarization curves and weight loss for the short-circuited and insulated specimens, and exposed to two different flow rates (0.5m/s and 5.0m/s) of seawater at 25°C also on the galvanic curren betweent short-circuited specimens. A three dimensional boundary element analysis of the potential and galvanic current density distribution for the differential aeration cell in the experiment was also performed. The computational and experimental results matched well. These studies demonstrated that the differential aeration cell corrosion owing to differential flow rate in seawater can be treated in an analogy as galvanic corrosion.
This paper deals with SCC and pitting corrosion resistance of 6061 and 7075 Al-base metal-matrix composites (MMC) manufactured by using the squeeze casting methods in the laboratory. SiC-whisker, Al2O3 and carbon fibers are used as reinforcements. SSRT can be applied to evaluate the MMC's resistance to SCC. Resistance of MMC to pitting corrosion can be determined by potentio-dynamic polarization to measure pitting potential. Transmission-electron-microscopy (TEM) can be used for observation of interfacial layers formed between the metal-matrix and reinforcements. When MMC is polarized in 3.5% NaCl solution, changes occurs in cathodic reaction due to the effect on the interfacial layers between the reinforcement fibers and the matrix. It can be found, however, that reinforcement fibers in MMC have no effect on the development of pitting and SCC susceptibility of MMC unless their conductivities are not shown. In other words, chemical composition and heat-treatments applicable to improve the localized corrosion performance of 6061 and 7075 Al-alloys are still effective to increase the localized corrosion resistance of MMC despite the difference in the critical stress of SCC.
When an arterial prosthesis is implanted in a patient, the prothesis must maintain a pathway for blood along its entire length. At the present time, the vascular prostheses with a diameter larger than about 6mm are clinically used successfully, but there is continued need for the vascular prostheses with a smaller internal diameter. The major problem is that the thrombogenicity of vascular prostheses frequently limits their clinical usefulness. In developing vascular prostheses, it would be important to understand the mechanisms of thrombus formation and blood coagulation. Also, it would be important to develop new techniques for evaluating antithrombogenicity of artificial materials in vitro prior to implantation. In this paper, the trend in designing and developing the vascular prostheses including hybrid vascular prostheses will be outlined. Also, the mechanisms of blood coagulation and thrombus formation, and functions of endothelial cells will be outlined. A new rheological method to measure the process of coagulation of blood in contact with foreign surface is shown, which will be available for in vitro evaluation of antithrombogenicity of vascular prostheses as well as for elucidating the mechanisms of thrombus formation and blood coagulation.