Zairyo-to-Kankyo
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ONLINE ISSN: 1881-9664
PRINT ISSN: 0917-0480

Zairyo-to-Kankyo Vol. 43 (1994), No. 10

  • ACM (Atmospheric Corrosion Monitor) Type Corrosion Sensor to Evaluate Corrosivity of Marine Atmosphere

    pp. 550-556

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    The ACM (Atmospheric Corrosion Monitor) type corrosion sensor which consists of a Fe-Ag galvanic couple was developed and applied for the evaluation of corrosivity of marine atmosphere. The sensors were exposed at two different sites, Shimizu in Shizuoka prefecture and Nishihara in Okinawa prefecture, and renewed every month. The temperature, relative humidity (RH) and the outputs of the sensors, I, were recorded in the microcomputer. Some sensors were exposed for more than one month at Shimizu. The sensor was found to be functional at least for two months. By analyzing magnitude and time variation of I, rain, dew and dry periods could be distinguished and their duration could be determined. By referencing to the empirically determined I-RH calibrating curve, the amount of deposited sea salt, Ws, could also be estimated. After the deposited sea salt was washed away by the rainfall, the sea salt was redeposited and Ws increased with time until reaching a stationary value. At Shimizu, a stationary value of 1.3×10-3mg/cm2 was reached after 3-4 days, while at Nishihara, a stationary value of 1.9×10-2mg/cm2, which is about ten times as much as that of Shimizu, was reached after 1-2 days. It is considered that the corrosivity of each site can be evaluated with these environmental parameters.
  • Metal Dissolution under Cathodic Current

    pp. 557-563

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    It has been comfirmed that the metal dissolution occurs at the cathode where enormous hydrogen gas bubbles are evolving in sulfuric acid, hydrochloric acid and electropolishing solutions. The rates of dissolution are much higher at the cathode than at the anode, and comoparable to those at the active corrosion potentials. The oxidizing ions such as HCrO4- and NO3- considerably increase the dissolution rates by the depolarizing effect at the cathode. It has been proposed that the dissolution occurs at the localized anode where is shielded by hydrogen gas bubbles due to the cathodic reaction.
  • Evaluation on Corrosion Test by Fuzzy Set Theory

    pp. 564-569

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    Fuzzy set theory was developed by Dr. Zadeh in America in order to treat some fuzzy problems in human decision or thinking and so on.
    In this paper, fuzzy set theory is applied on corrosion test data as follows;
    (1) fuzzy IF-THEN rules is made depending on corrosion data by veteran engineer and some engineering information,
    (2) membership functions of IF-part and THEN-part are specified,
    (3) through fuzzy inference calculation, some predictions of corrosion data are expected.
    Results of fuzzy inference method are compared with real data of corrosion, and similarity to both data may be recognized.
  • Fracture Mechanism of Hydrogen Assisted Cracking of a QT-treated Low Alloy Steel Estimated by AE Moment Tensor and Source Wave Analyses

    pp. 570-579

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    A new system for the source inversion processing and the moment tensor analysis of elastic waves was developed and utilized to elucidate the fracture kinetics and kinematics of hydrogen assisted cracking (HAC) of a QT-treated low alloy steel. The system consists of 8 channels. Seven channels is utilized to measure the arrival time and the amplitude of the longitudinal waves of the AE signal caused by the microcracking and the other to measure the out-plane displacement. The source location for AE signal and the moment tensor were, respectively, computed from the difference of the arrival times and from the relative amplitude of the longitudinal waves. Fracture kinetics was deduced by the inversion processing of the measured displacement with the Green's function of the second kind. The tensor analysis revealed that most cracks in HAC were caused by the quasi-cleavage fracture whose shear ratio was less than 40%, however, the Mode-II shear fracture connecting the isolated the Mode-I cracks, and the Mode-II fracture of vertical crack were also found to occur during HAC. The crack size and its evolution rate were found to change from place to place and with the testing time. The system can make clear “what kind of fracture occurs, at what rate, and where”.
  • On the Requisites for Cathodic Protection of Buried Steel Pipes in the Presence of Sulfate-Reducing Bacteria

    pp. 580-587

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    Laboratory free corrosion tests and cathodic protection tests were carried out to investigate requisites for achieving complete cathodic protection on the steel pipes buried in the microbially active soils containing sulfate-reducing bacteria (SRB, Desulfovibrio desulfuricans) with other species of bacteria. Off-potentials were changed over a range from -0.7 to -1.3V (vs. Cu/CuSO4). The results obtained can be summarized as follows:
    (1) Comparative free corrosion tests between non-sterile and sterile systems clearly revealed that the presence of SRB can be stimulatory to soil corrosion, (2) Practical sufficient protection in active SRB clayey soil was shown to be obtainable at the off-potentials more negative than -0.9V and/or under the cathodic current densities of not less than 0.05Am-2. (3) The hydrogenase activity of SRB was shown to be active even under the cathodic protection conditions and playing an important role in the protection process by stimulating the formation of protective sulfide films.
  • Fiber Reinforced Thermoplastic Composites

    pp. 588-596

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    Fiber reinforced thermoplastic matrix composites (FRTP) offer several advantages over conventional thermosetting matrix composites (FRP). These include short process cycle times, reformability, and enhanced performance in fracture toughness, damage tolerance and so on. This paper will present an updated overview of the processing methods for thermoplastic matrix composites, and the various properties such as mechanical, thermal, electrical properties and a few problems in processing of FRTP will also be reviewed and discussed.
  • Cathodic Protection of Buried Pipelines Affected by Stray Current Electrolysis

    pp. 597-598

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