The corrosion rates of mild steel in a tap water with and without inhibitors were measured under heat transfer and non-heat transfer conditions. Under heat transfer conditions the corrosion rate of mild steel was larger than that measured under non-heat transfer condition. From the results, it was found that the corrosion rate was affected more pronouncedly by the magnitude of heat flux than the temperature at the heat transferring surface. The corrosion rate of mild steel in water containing sufficient concentrations of corrosion inhibitors under heat transfer conditions was almost equal to that under non-heat transfer conditions. The corrosion inhibition occurred at the same concentration of inhibitor for both the heat transfer surface and the non-heat transfer surface. Therefore, it appears that the evaluation of corrosion inhibitors under heat transfer condition will give nearly the same result as that obtained under non-heat transfer conditions. In other words, the effects of inhibitors on the corrosion of heat transfer surfaces can be evaluated by the corrosion measurement of test coupons in laboratory and field without taking heat transfer into account.

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Anodic oxide film formed on cobalt in sodium borate solution at pH=11.0 have been investigated by coulometry and potentiometry. The potential change during galvanostatic oxidation exhibits three plateaus before the potential reaches a steady state value for oxygen-evolution reaction. In the first plateau Co(OH)₂ is formed on cobalt. Further oxidation at constant current leads to a potential rise which accompanies the formation of CoO layer between the cobalt metal and the Co(OH)₂ film. In the second plateau a reaction of CoO·nH₂O to Co₃O₄ occurs with a coulomb equivalent to the reaction. This Co₃O₄ film is oxidized to Co₂O₃·mH₂O in the third plateau, the potential of which is 0.575V (she) not depending on the current densities and probably corresponds to the equilibrium potential of Co₃O₄/CoOOH. This change of Co₃O₄ to Co₂O₃·mH₂O, however, does not complete during the potential arrest at the third plateau. From the galvanostatic-cathodic reduction of the films formed at constant potential and at constant current, the primary passive film formed in the potential range from -0.455V to +0.22V (she) is estimated to be CoO·nH₂O, the secondary passive film in the range from +0.22V to +1.1V to, be mainly Co₃O₄, and the transpassive film at potentials more positive than 1.1V to be Co₃O₄ and Co₂O₃·mH₂O. In the potential region of the secondary passivity (0.2V to 0.45V), both CoO·nH₂O and Co₃O₄ are formed under potentiostatic conditions and the ratio in amount of Co₃O₄ to CoO·nH₂O increases with rising potential. In this potential region, CoO·nH₂O is first formed and then gradually changes to Co₃O₄ at constant potential.

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The application of the polarization resistance method to the corrosion rate measurement of mild steel in hot salt solution under extremely low contents of dissolved oxygen was discussed. In environments of 6wt% NaCl solution where such factors as dissolved oxygen content (<1-100ppb), pH (4.5-7.5), temperature (60-95°C) and additive ion (Mg²⁺ or SO₄^2-) were changed, the cathodic polarization (ΔE) was measured by appling a constant current (I_app) for 1 minute at intervals during test periods and the polarization resistance (R_p) was calculated from ΔE and I_app. It was confirmed by colorimetric analysis of the amount of dissolved Fe²⁺ in deaerated 6wt% NaCl solution at pH 4.5 that the variation of 1/R_p with time agreed with that of corrosion rate. Under the above various conditions, the average values of 1/R_p calculated from graphic integration of the 1/R_p vs. time relations were proportional within ±30% errors to the average corrosion rates determined by the weight loss. Based on this proportional relation, it was assumed that the instantaneous corrosion rate of mild steel in seawater or brine under deaerated conditions could be determined by the measurement of polarization resistance. In the present work, the cathodic polarization generally attained to the steady state within 1 minute, but the unsteady state of polarization was rarely obtained at the higher temperature. It was considered that further studies might be necessary to clarify the time of current charge under such unsteady polarization.

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This paper reviews corrosion and its prevention of condenser tubes with the special references to our experiences and researches on copper alloy condenser tubes. In the first part, the research activities which has resulted in a successful development of condenser tubes are briefly summarized and the background of the necessity for further researches and developments in condenser tubes is described. In the second part, after a brief introduction to engineering copper alloys for condenser tubes, some metallurgical factors, such as composition and heat treatment are discussed in detail. Practical and/or trial applications of stainless steel condenser tubes in U. S., U. K. and Japan are introduced. In the third part, several important corrosion phenomena are described as follows based on our experiences and researches. Statistical survey on malignant impingement attack of aluminium brass tubes reveals that the attack is closely related to the precipitation of MnO₂ rich film onto the tube surface, which is caused by chlorination of sea water contaminated with manganese. Three modes of relationship between sand erosion and sand contents are demonstrated in connection with the film formation and the abrasive action of sands to the film. Successful data of application of AP bronze condenser tubes in polluted sea water are shown. Importance of protective initial film formation is stressed, especially for aluminium brass tubes used in polluted sea water. In the fourth part, the statistical data of the leakage troubles of condenser tubes in Japan are presented together with those in U. S., which reveals the prominent improvement of service data of Japan in these few years. In the fifth part, our experiences on the galvanic corrosion of Naval brass plates caused by coupling with titanium tubes and hydrogen absorption of titanium tubes due to cathodic protection of Naval brass plates are described. As a result, it is suggested that not only the solution of present-day problems but also future advances in materials development will be possible through a better understanding of the film formed on the tube surface.

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