Cathodic protection of impressed current system was applied to submarine pipelines of 18 in, 20 in, and 30 in in diameter and about 9.2km in total length, at T Refinery, I Co., Ltd.
In potential measurement of submarine pipelines, the negative terminal of a voltmeter is usually obligated to be taken at the end point of pipelines, even if the point to be measured is very far from the end, and so measured values should be corrected considering the given conditions.
In this paper, calculations are carried out under these considerations to get a correct potential distribution curve applying suitable formulae for measured values, and protective performance and interface resistance of each pipe were confirmed.

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The effects of heat treatment on sulfide corrosion cracking of several martensitic and ferritic stainless steels were investigated. Sodium chloride solution saturated with hydrogen sulfide and containing acetic acid was adopted as corrosive medium. The results of this study may be summarized as follows:
1) With 410 steel, all of the specimens austenitized at 1, 150°C, followed by an oil quenching and tempered at various temperatures in the range from 300 to 800°C were cracked in one week or less, but the appearances of the crack varied with tempering temperatures as shown in Fig. 1. Cracking was of intergranular path with respect to the former austenite when tempered in the range from 550 to 700°C for short periods of time, but changed to transgranular with increase of tempering time.
2) With 430 and 7 Cr-Si-Al steels, fine cracks of limited length and blisters appeared in all of the specimens treated at 1, 150°C, followed by an oil quenching and annealed at various temperatures in the range from 300 to 800°C. Paths of crack are predominantly transgranular. But when the specimens are annealed in the range from 550 to 750°C, cracks are partly transgranular (in the ferrite grain) and partly intergranular (when encountered with former austenite grain).
3) 410 steels oil-quenched at 1, 300°C and annealed at various temperatures displayed a similar trend to that found in 430 and 7 Cr-Si-Al steels.
4) With 25 Cr-2.5 Ni steel, no cracking was observed during the 10 days test periods used.
5) Variations of mechanical properties with time of exposure to corrosive medium are described.

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The interrelation between the measured values by cell voltage-current curve method and those by potentiostatic polarization method was investigated, as both of the electrochemical corrosion-testing methods are commonly applied to select suitable metallic materials withstanding given corrosive environments.
Corrosion tests of the metallic samples, austenitic stainless steels and titanium, were carried out in 0.5N HCl soln. or 0.5N H₂SO₄ soln, at room temperature. There existed clearly an interrelation between the measured values of the two different testing methods when the metals were in the active or passive regions. In addition, it was also indicated that the effect of cathodic polarization to cell voltage-current curves could be completely nullified if the area ratio of cathode to anode was more than 10, and that thereby potentiostatic result could be obtained.

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