This paper describes characteristics of scaling mechanism in open cooling systems. The results obtained are summarized as follows: 1) Scaling of total hardness is closely related to that of silica; the probability for total hardness scaling is in inverse proportion to a value of total hardness/silica in make-up water. 2) Scaling mechanism has tow types. When total alkalinity is low, deposition of magnesium silicate dominantly occurs and high total alkalinity of make-up water accelarates scaling of calcium and then silica may act as a catalyst to the deposition of calcium carbonate. 3) Scales aboundant in silica and magnesium cause less troubles, while calcium rich scales detriorate heat-exchange performance. 4) Calcium carbonate deposition does not occur in cooling water of positive Langelier index (with total hardness as high as 500mg/l), if total alkalinity is low. Scaling in low alkalinity water is due to the synergism of hardness and silica, while in high calcium hardness and total alkalinity water calcium carbonate deposition occurs in accordance with Langerlier's expression.

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To investigate the effect of a small amount of additional elements on the selective dissolution characteristics of Al-4%Zn-1.4%Mg alloy an immersion corrosion test and electrochemical measurements were carried out. On this alloy, not intergranular dissolution but selective dissolution within grain could be observed after precipitation heat treatment, and the grain boundary remained unattacked. The phenomenon occured also on the alloy containing a small amount of Cu. On the other hand, intergranular selective dissolution could occur on the alloy containing Mn, and prominent intergranular corrosion was observed on the alloy containing Zr and Cr in addition to Cu and Mn. This kind of dissolution configuration could be well understood in terms of electrochemical polarization characteristics on the phases which could be formed by precipitation heat treatment. A galvanostatic anodic dissolution in the acidic chloride solution would be effective and convenient for the rapid estimation of selective corrosion characteristics.

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A large number of industrial plants and facilities of Japan is often constructed on the seaside area, and so steel materials of these plants and facilities are mostly located under the corrosive environment by sea-salt fine particles. These steel materials are, of course, protected by means of paints, platings or other galvanic protection methods, but some problems to investigate seem still to remain for gaining the better corrosion prevention in such a corrosive environment. In this paper, the results of outdoor atmospheric exposure test by using the small painted specimens are described. The exposure test was practised on the seashore at Tokai Research Establishment of Japan Atomic Energy Research Institute for fourteen months.
In this test, it was proved that blasting and control of film thickness could somewhat improve the grade of rust prevention of the exposed specimens, but that melamine-alkyd resin painting systems (total film thickness; 12-36μm) were generally insufficient for a long time rust prevention system in the presence of sea-salt fine particles. On the other hand, the specimens using zinc rich paint primer or hot dip galvanizing as undercoatings (total film thickness; 173-495μm) showed the perfect corrosion resistant properties against the corrosive environment of the test site under the influence of sea-salt fine particles. Moreover, even the specimens of the paint films which were artificially scratched in the shape of cross cut got hardly rust on the bare steel area and no deterioration was found on the paint films.

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The effects of the weld heat input and the pipe wall thickness on the intergranular stress corrosion cracking (IGSCC) behavior of 304 stainless steel pipe welds were studied by means of the CBB test in simulated boiling water reactor environment. Results are summarized as follows. (1) As the weld heat input becomes higher, the IGSCC susceptible region in the weld heat affected zone (HAZ) becomes more distant from the weld fusion line. However, the IGSCC susceptibility itself is not uniformly related to the weld heat input in such a manner that the IGSCC susceptibility at a weld heat input of 1, 000J/mm is rather higher than that at 2, 000J/mm. (2) As the pipe size (pipe wall thickness) becomes larger, the IGSCC susceptible region in HAZ becomes closer to the weld fusion line, and also the IGSCC susceptibility itself becomes higher. (3) These behavior are described from the viewpoints of the chromium depletion theory based on analytical results of the weld heat cycle.

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The return period is widely used on probability papers which are essential tool in the analysis of extreme values and/or dimension effect (the so-called size effect). Several considerations are indispensable in the application of the tool, however, because it requires sometimes uncertain extrapolation on the probability paper for extreme values. The problems are illustrated with corrosion pit depth data which are distributed doubly exponentially. Then a new analyzing method is proposed in connection with correct application of the return period for recognizing a reliable size effect. The possible usage of the first asymptotic distribution of the smallest values is also suggested in corrosion and its related field.

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