Pitting failures of copper tubes in hot water were investigated in detail. Sample tubes from various tubing lines were collected at three buildings in Tokyo. Two cases of the three were similar and their results are summarized as follows: (1) Water was characterized by high levels of SO₄^2- and Cl^-, and low ratio of HCO₃^-/SO₄^2- in comparison with the averages of Japanese river water; (2) Pits were covered with mounds of greenish blue corrosion products containing Cu₄SO₄(OH)₆; (3) Pits contained reddish brown products of Cu₂O. Chloride was concentrated at the bottom of the pits, where crystalline CuCl was detected in some cases; (4) The pH value within the pits was 3 to 4. These characteristic features suggest that the pitting corrosion of above cases is classified Type II as many other cases experienced in Japan. It is considered that Cl^- in water first forms CuCl as a corrosion product which may hydrolyze to develope an acid and Cu₂O in the pit, and that SO₄^2- forms the mound of Cu₄SO₄(OH)₆ on the pit, which hinders the acid solution to be washed away from the pit. The low level of HCO₃^- (low buffer capacity) is in favor of the ready decay of pH value in the pit.
Pitting corrosion of the third case showed some different features, particularly with respect to water quality. Since this type of pitting has rarely been reported in Japan, it is difficult at this stage to explain its mechanism.

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The potential change of corroding systems responding to the repetitive square wave current was deduced theoretically. The corroding systems were simulated by a linear circuit which was constructed with polarization resistance, solution resistance and capacitance due to electrical double layer. The potential change, where the response reached a steady state, was obtained as
δΔE_m=I₀[(R+R_s)M(t, 2p)-(2R(-1)ⁿexp{(n+1)p-t/CR})/(exp(p/CR)+1)]
where I₀ is the amplitude of applied square wave current, R_s, solution resistance, R polarization resistance, M unit square wave function, t time, p period of square wave, and n the maximum integer which does not exceed t/p. From this equation several ways of separating R, R_s, and C, from each other were proposed being based upon the following relations.
δΔE_m(t=np)=2I₀R_s, ΔE_p(p→∞)=ΔE_p(f→0)=2I₀(R+R_s)
ΔE_p(f→∞)=2R_s, {∂ΔE_p/∂(1/f)}_(1/f→0)=2I₀/C
where δΔE_m(t=np) is potential change at the instant of polarity change and ΔE_p is the peak-to-peak value of potential change. Finally, the feature of this method was discussed.

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The stress corrosion crack growth behavior of sensitized Type 304 stainless steel has been investigated during the slow strain rate test (SSRT) in high temperature water. The test was done on center-notched thin plate specimens. An optical direct observation system, consists of single crystal sapphire windows, was employed for crack growth measurements. The specimens suffered large scale yieldings during the SSRT. Obtained crack growth rates were analyzed with six kinds of dynamic parameters; the extension rate, the net section nominal stress, the stress intensity factor, the J integral, the time differential of J, and the modified J integral (C* integral). The analytical results indicated that the J integral and the time differential of J (dJ/dt) well figure out every data obtained at different extension rates. Particularly in crack growth mechanism, the dJ/dt seemed to be the most useful parameter. The crack tip deformation rate controls the dynamic SCC growth rate in film rupture model, and the dJ/dt corresponds to the deformation rate. It is also suggested that the crack growth rate analysis by the dJ/dt during SSRT can be consistently understood corresponding to that by a frequency in cyclic loading.

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An interruption by sulfate ion on the inhibitive effect of aluminium ion for iron corrosion in water has been investigated. The inhibitive effect of aluminium ion was found to be markedly deteriorated when the water contained sulfate ion. In the absence of sulfate ion, a thin and compact protective film of hydrated aluminium hydroxide was formed on the surface of the specimen during the corrosion, while in the presence of sulfate ion a dense film with many cracks of polynuclear sulfatecontaining oxy-aluminium complex was found to be formed, which caused a considerable deterioration of the inhibitive effect of aluminium ion. In order to overcome this defect, many additives that act co-operatively with aluminium ion were examined, whereby 2-mercaptobenzothiazole and some related compounds were found to be very effective.

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