The soil-corrosion investigation which was started in 1922 was originally planned to cover 12 years, plus the time required to write the final report. In 1934 the last of the original specimens were removed from 23 soils, but additions to the original test have so altered the plans that there now remain in the ground 7,500 specimens buried by the National Bureau of Standards and approximately 2,000 specimens of protective coatings prepared by r esearch associates.In general, the results of the examination of the specimens r emoved in 1934 confirm earlier conclusions. The additional data p ermit the calculation of the standard errors for certain classes of data.The average maximum penetrations for the wrought-iron, Bessemer, and open-hearth !?pecimens do not differ by more than a few percent. The IIpecimens of open-hearth iron and of open-hearth steel containing 0.2 percent of copper apPear to pit slightly more deeply than the other wrought specimens. In some soils cast iron corrodes somewhat more rapidly than st eel.Soils differ so greatly in corrosiveness that the average rates of corrosion or the average life of a pipe have little practical value.The addition of chromium to steel reduces the loss of weight by corrosion and the number of pits, but even a large percentage of chromium will not prevent serious pitting. This is especially true with respect to soils containing chlorides. The addition of nickel, with or without chromium, tends to reduce the depth of the pits.Certain materials seem to be especially suited or unsuited to certain types of soils.
^^°f C °rrOSi0n due t0 Stra ^electric c ^rents in the earth by the American Committee on Electrolysis and the Bureau of Standards Ye g o a 2nf wing ']Soil-Corrosion Studies 453 sis, it appeared best that the pipe materials used in the investigation should be selected from stock and include the various kinds and grades of pipe ordinarily purchased by public utility companies. This decision materially affected the data subsequently obtained, for stock pipes and fittings necessarily vary somewhat in size, composition, and metallurgical history; these variations result in inconsistencies in the corrosion data and interfere with the construction of a theory as to why certain results were obtained.The lack of uniformity in the materials tested and the lack of complete knowledge concerning these materials make them somewhat unsuitable for the study of the fundamental principles of corrosion.If the purpose of the investigation had been such fundamental studies, the arrangements would have been altogether different. The results which may be obtained should have a considerable value for the public utility owners interested in the maintenance of underground pipe systems.To the original materials selected for study there have been added so many others of widely different characteristics that a logical arrangement of the data on the tests is difficult. On this account the data applicable to all or most of the materials will be given first, while the data on the individual materials will be presented in that section of the paper dealing with the tests' of the group of specimens to which the material can best be assigned. In order that the general reader may get a picture of the materials involved, they are listed below. The materials tested were buried at different times, and it will be necessary to refer to detailed data sheets in order to determine dates of burial and removal. The figures preceding the names of the specimens indicate the approximate number of specimens buried. Numbers and kinds, of specimens buried A. Unprotected pipe and other specimens buried in 1922 in approximately 46 soils: 552. Bessemer steel, butt-welded, 13^-inch pipe. Yfomanf wing '] Soil-Corrosion Studies 455 I. Metallic protective coatings applied to steel pipes and buried in six soils; buried in 1924 and 1928: 48. Calorized pipe, dry process. 48. Calorized pipe, wet process. 36. Lead-coated pipe. 98. Galvanized pipe (3 base materials). 72. Galvanized copper-bearing Bessemer sheet, 16-gauge, 3 weights of coating. 48. Galvanized open-hearth iron sheet, 16-gauge, 2 weights of coating. 24. Galvanized open-hearth iron sheet, 18-gauge, 1 weight of coating. 48. Galvanized copper-bearing Bessemer sheet, 18-gauge, 2 weights of coating. 72. Black sheet, 18-gauge, 3 materials (checks). J. Bituminous coatings applied to steel pipe and buried in 1922 in 31 soils: 62. Asphalt dip. 62. Asphalt-impregnated fabric wrapping. 62. Coal-tar pitch dip. 62. Coal-tar pitch impregnated fabric wrapping. K. Bituminous coatings applied to steel pipe and buried in 46 soils i...
Instructions are given for the several uses of the apparatus. The care of the instrument and the precautions necessary for obtaining reliable data are discussed.In the last part of the paper the interpretation of data is considered and the results of field work are quoted to show that the earth-current meter gives more reliable information regarding electrolysis conditions than can be obtained otherwise. CONTENTS
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