The inhibition effect of compounds with double bonds on the corrosion of pure iron was studied in a 6.1M HCl solution by polarization measurement. The compounds used as the inhibitors were hydrocarbons, alcohols, carboxylic acids, ethyl esters, halogenated compounds, mercaptans and amines containing C₂-C₆ non-polar group with and without a double bond. The inhibitor with the double bond inhibited the cathodic process rather than the anodic one, and was more effective than the corresponding compound without the double bond. Relationship between the inhibition efficiency and the polar substituent constant of the non-polar group showed that the adsorption by the action of the polar group was of little importance to the inhibition. Both delocalized unshared electrons of the polar atom and delocalized π-electrons of the double bond in the inhibitor molecule were concluded to play an important role in the enhanced inhibition efficiency of the compound with the double bond. It was considered that back-coordination of metal electrons to the vacant orbitals of the inhibitors cooperated with the donation of electrons to the metal orbitals in the chemical adsorption of the effective inhibitors.

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Some Preventive Methods for SCC were studied on vertical heat exchangers of austenitic stainless steels in which the field cooling water was on the cell side. The results obtained are as follows; both the normal type (expanded and seal welded type) and the strength welded type heat exchangers caused SCC from the cell side withers a year. The normal type heat exchangers using aluminum sprayed tubes suffered from SCC after 5-6 years service. In normal type heat exchangers whose tube sheets were SUS 316L cladded steels, SCC occurred in the tubes at the upper tube sheet after 1-3 years service. However, no SCC was observed at the position of the lower tube sheet even after 6 years service. A practical preventive method for SCC has been found by using the stainless cladded steel as the tube sheet and the aluminum sprayed tubes as heat exchanger tubes at the same time.

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The fracture mode in stress corrosion cracking of several stress corrosion cracking tests of austenitic stainless steels in boiling MgCl₂ solution was fractographically investigated by scanning electron microscopy. The results obtained are as follows: (1) The fracture mode depended on stress corrosion cracking testing method under the same environmental condition. Namely, transgranular fracture was observed in stress corrosion cracking of U-bend tests and WOL tests where K_I was below about 37MPa√m, while intergranular fracture was found in the transitional region from transgranular fracture to mechanical ductile fracture in both constant load tests and slow strain rate tests. (2) The effect of alloying elements on the fracture mode was revealed in the intergranular fracture in both constant load tests and slow strain rate tests. P, N and Mo promoted susceptibility to intergranular fracture, while Si acted to prevent susceptibility to intergranular fracture.

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For the purpose developing an insoluble anode, nickel-tantalum and nickel-niobium alloys of 19 different compositions were prepared by vacuum arc melting and electron beam remelting processes. Anodic behavior of the alloys was studied in 0.5M H₂SO₄ and 1M NaCl at room temperature. The results showed that hypo-eutectoid nickel alloys containing less than 30wt.%Ta(Nb) dissolved severely both in sulfuric acid and in chloride solution at an anodic current of 5A/dm². The intermetallic compound, Ni₃Ta(Ni-50wt.%Ta) showed the lowest dissolution rate of 0.3g/A·Y and 1.69V vs. SCE in 0.5M H₂SO₄, while the compound Ni₃Nb showed somewhat higher dissolution rate in sulfuric acid under the galvanostatic condition. Electrode performance of the berthollide compound, Ni₃Nb was better in 1M NaCl than that in 0.5M H₂SO₄. However, the lowest dissolution rate of the alloy in 1M NaCl was 6.2g/A·Y at 5A/dm². Electron beam remelting of the alloys decreased chlorine and oxygen overvoltage remarkably and improved their electrochemical properties for the insoluble anode.

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The studies related to hydrogen damage of stainless steels have been reviewed with emphasis on the recently published results. This review is composed of seven items, preface, diffusion and trapping behavior of hydrogen, internal hydrogen embrittlement, hydrogen environment embrittlement, hydrogen damage at the elevated temperature, creep behavior in hydrogen environment, and anomalous corrosion by hydrogenation. Special attention is given for hydrogen damage of austenitic stainless steels.

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