Evaluation of sand erosion-corrosion resistance of metallic materials was required for selecting an appropriate material to construct a pump to be used for raising particles carried in a strongly corrosive liquid. Three types of testing facilities were adopted: Stauffer's Grinding Pot Device, a magnetostriction vibratory cavitation eorsion testing facility and the newly developed magnetostriction vibratory sand erosion testing facility. The Stauffer's Device produced an unexpected result: the weight loss of test specimen under erosion-corrosion conditions was smaller than that under pure erosion conditions. The root cause is that the eroded and corroded areas on the specimen surface are not equal: the front side surface is eroded as well as corroded by the slurry stream, while the rear side surface is only corroded. We have to conclude that the Device is not suitable for an erosion-corrosion testing method. No such inexpedience was occurred in the results obtained by the magnetostriction vibratory facilities where the eroded and corroded areas on the specimen surface are completely coincide. The mechanical properties of the test specimen, however, produced a larger influence on the results obtained by the vibratory cavitation test in compared with that on the results obtained by the vibratory sand-erosion test. Thus, it was concluded that a cavitation erosion-corrosion test can not be substituted for a sand erosion-corrosion test.

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The passive films formed on Pb and Pb-Ag alloy (1 and 4wt% Ag) in 0.05 to 1M NaCl solutions have been studied by a linear potential sweeping method, potentiostatic and galvanostatic measurements. On the way to passive region of the E-I curves obtained by linear potential sweeping experiments, two distinct current peaks, peak 1 and peak 2, were observed at the concentration of 0.25M or above. An oxidation mechanism in term of peak 1 and peak 2 is proposed and discussed. It follows from comparison of Pb and Pb-Ag alloy that the use of Pb-4wt% Ag alloy induces a negative shift in oxygen evolution potential, but does a positive shift in film-dissolution potential. In addition, the alloy has a tendency to reduce slightly the retention current of passivation. The passive films, formed on both Pb and Pb-Ag alloy, have the structure which the inner layer is composed of PbO and PbO₂, and the outer layer of PbCl₂ and Pb(OH)Cl.

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Metallurgical examination and simulation test of stress corrosion cracking (SCC) were carried out to reveal the cause of SCC of Hastelloy C test vessel in hot concentrated sodium chloride solution The following results were obtained.
(1) SCC occurs from pits and develops along grain boundaries at which intermetallic compounds such as P phase and Ni₇Mo₆ precipitated because of welding heat or heat treatment.
(2) Susceptibility to intergranular corrosion at precipitated grain boundaries is very high in oxidizing environment.
(3) The brittle mode of intergranular fracture with geometric pattern was observed on the SCC fractured surface of the heat treated specimen. It seems that such mode was formed due to the effect of precipitated phases.
(4) From the point of view of the material, residual stress due to welding and high susceptibility to intergranular corrosion due to precipitation of intermetallic compounds are dominant as a cause of SCC. From the point of view of environment, diffusion of reactive species in solution such as concentration of chloride ion and supply of oxygen is dominant.

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The effect of dissolved oxygen on corrosion inhibition of Cr-Mo steel using sodium nitrite, which can be added to the circulating cooling system of marine diesel engines as a corrosion inhibitor, has been investigated in pure water with 50ppm SO₄^2- by means of the polarization resistance method and weight loss and the corrosion potential measurements. In corrosion rates over 10mdd, there was a linear relation logarithmically between corrosion rates and polarization resistance in NaNO₂-SO₄^2- ion solutions, and critical values for polarization resistance existed in the corrosion-inhibition interfacial region. When sodium nitrite more than the critical concentration required for corrosion inhibition was added, the good inhibitive effect is obtained. On the other hand, when the sodium nitrite was added under the critical concentration in the solution with high dissolved oxygen corrosion was accelerated by the depolarization of oxygen, but corrosion was retarded with low dissolved oxygen. It can be concluded that the inhibitive action of sodium nitrite results in the formation of the adsorbed layers of nitrite ion and dissolved oxygen stimulating the passivation of the steel surface.

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The present review is composed of four items, preface, conditions required for the inhibitors, inhibitors list and important chief inhibitors, including calcium ion, aluminium ion polyphosphates, polysilicates, phosphonates, molybdates and some other ones.
Special attention is given for nonpoluting inhibitors throughout the review.

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