From corrosion survey of burned pipelines, several interesting results were obtained as follows.
1) Cathodic protection utilizing A. C. stray current:
The underground water pipelines in a certain industrial area were cathodically protected by making use of alternating stray current with simple arrangement which merely comprised driving earth pipes (size: 34mmφ×10m) into ground near the pipelines and connecting them electrically to the pipelines through silicon diodes.
2) Relation between gas-pipe-to-soil potential and current in a certain city:
On the gas pipelines which have the drainage system to electric railway, relation between the pipe-to-soil potential and the line current was examined. The relation curve showed hysteresis for a certain range of line current. This phenomenon was considered to be related to the polarization of pipeline surface.
3) Case of cathodic protection for pipelines in some cities:
These pipelines having tendency of suffering from stray-current corrosion, could not drain the current to electric railway for several reasons, and were too small to apply the expensive impressed-current method. Therefore, the method by earth pipe with low resistance was adopted to get the drainage effect. The result of experiments showed that the better effect of drainage was obtained for the lower resistance of earth pipe and the higher resistance of pipe-surface coating.

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In the conventional catholic protection by impressed current system of one-step transformer-rectifier type, there has been the disadvantage that the power loss in the direct current wiring circuits was quite large because of large current in the circuits.
A new cathodic protection system, which consisted of a main control transformer and some numbers of small transformer-rectifier sets installed in short distance from electrodes, has been developed.
In the new cathodic protection system, the power loss in the wiring circuits is almost negligibly small because of much shorter direct current wiring circuits.
Some technical problems concerning the design, installation and field experiences of the newly developed two-step transformer-rectifier cathodic protection system for marine structure are discussed.

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In order to investigate the influence of the nature of corrosion products on apparent difference in the susceptibility to sulfide corrosion cracking between nickel-free and nickel-containing high strength steels, the corrosion products formed on surfaces of these steels in hydrogen sulfide aqueous solution have been compared and discussed by means of optical microscopy, X-ray diffraction and electron diffraction. The corrosion weight losses of the steels in the similar medium were also determined.
The results are summarized as follows:
1) The corrosion product formed on the steel surface in saturated aqueous hydrogen sulfide appears to be composed primarily of tetragonal iron sulfide and it is not kansite as so far considered.
2) Nickel in these steels acceralates the crystallization of tetragonal iron sulfide formed on the steel surface.
3) Nickel also increases the corrosion rate of the steels in hydrogen sulfide solution.
4) The structure of corrosion products in the initial stage of corrosion reaction differs from that of nickel-containing steel to that of nickel-free steel and the difference in the structure of sulfide becomes more distinctive after aging. The particular sulfide formed on nickel-containing steel is believed to be relevant to the sulfide stress-corrosion cracking.

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