Corrosion. The use of steel for welded pipe was made possible, in the first place, through the manufacture by the National Tube Company of a special grade of low-carbon steel, equal in welding quality to the wrought iron which had formerly been exclusively used for this purpose. Steel pipe has in later years superseded wrought-iron pipe by proving its superiority in strength, ductility, and finally, as made under modern processes, by its superior durability. As manufacturers of both wrought-iron and steel pipe for many years, we have had a special interest in this question of durability, about which there has been so much debate, and with our dual interest have had exceptional opportunities to make comparison of these materials under all manner of service. Moreover, we have always shipped a wrought-iron coupling on steel pipe, so that in case there was any outside corrosion, a comparison of the two materials could be readily made under the same conditions. As a result of an extended study of this question in the laboratory and in the field, and with the experience of many large consumers of pipe, who have made careful observations from cases where both iron and steel pipe were used under the same conditions, there was no further room for doubt as to the advantage of steel pipe, made under our methods of manufacture, in respect to its resistance to corrosion, particularly as to pitting; hence we abandoned the manufacture of charcoal and puddled iron for welded tubes and pipe after January, 1909. For the information of those wishing to follow up the discussion of this subject, and obtain data regarding the tests and experiments which have been made on the relative corrosion of iron and steel, we give a list of publications below to which reference may be made: * Proceedings of Engineers' Society of Western Pennsylvania, 1907. T. N. Thomson, two reports, 1908-10, American Society of Heating and Ventilating Engineers. American Society for Testing Materials, 1906, 1908 (Howe). "Corrosion of Iron," A. Sang (McGraw-Hill Publishing Company). (Extensive bibliographs.) '' 'Corrosion and Preservation of Iron and Steel," A. S. Cushman and Hy. A. Gardner (McGraw-Hill Publishing Company). "Metallurgy of Iron and Steel," Bradley Stoughton. "Electrolytic Theory of the Corrosion of Iron and Its Applications," Wm. H. Walker (Journal Iron and Steel Institute, 1909). "Function of Oxygen in the Corrosion of Metals," Wm. H. Walker (Transactions American Electrochemical Society, Vol. 14, p. 175). "Corrosion of Iron and Steel," by J. N. Friend, 1911 (Longmans, Green and Company). "Corrosion of Boiler Tubes," Jour. Am. Soc. Nav. Engrs., May, 1904. National Tube Co. bulletins are published from time to time giving results of experience on this subject. Cause of Corrosion. There is hardly space here to go very deeply into the question of corrosion in all its phases, about which there is still some * An additional list of references will be found in appendix. (See index for difference of opinion, but a few underlying facts which have recently been well established by experiments may be useful to those interested in protecting the metal. It has been noticed by many who have worked on the problem of corrosion, that differences of electrolytic potential between two adjacent places on the surface of the metal causes local pitting. This difference may be due to lack of homogeneity in the metal, but more often is caused by foreign matter, electro-negative to iron, attached to the surface; such as mill scale, carbon, or rust itself. Without going into a discussion as to the fundamental causes, it has been clearly established that corrosion consists of two main reactions, viz.: the solution of a small portion of the iron in water, and the subsequent oxidation of the ferrous iron in solution to ferric hydroxide, which is then precipitated out as "rust." The amount of the corrosion is still further increased by the combination of free oxygen with the hydrogen, which was deposited on the surface of the metal when iron went into solution. This cycle of reactions is repeated, and the rust continues to accumulate so long as both water and air are present. Other agencies may accelerate the process of corrosion, but in the absence of either one of these elements no corrosion can take place. Steel will remain clean and bright for an indefinite time in dry air, and also in water that is free from air. Hence the necessity to see to it that, as far as possible, oxygen and other corrosive gases are removed from water, and that iron and steel exposed to moist air are protected by impervious and durable coatings. We invite correspondence on this subject with our research department. Mill Inspection and Tests. Every piece of pipe made in National Tube Company's mills is inspected for surface defects, and must stand an internal hydrostatic pressure test, without leaking, before shipment. Machines for applying this test are installed at convenient places throughout the mill. The amount of pressure applied depends on the use to which the pipe or tube is to be put, but in no case is it deemed advisable to test the finished pipe to more than one-half the elastic limit of the material, this being, however, as a rule, considerably above the actual working pressure. All boiler tubes and lap-weld pipe for certain purposes are subject to a flattening test made on the crop ends cut from each piece of pipe. This is done to insure strong welds and sound material. (For list of test pressures see pp. 68-76.) Besides the regular internal pressure tests described above, lap-welded boiler tubes for locomotive service are given individual inspection and tests at the mill as follows: 1. Inspection of external and internal surface (the latter by the aid of reflected light). 2. The ends on being cut off are placed in a flanging press, designed by us especially for this purpose. The rough end is first pressed flat by a horizontal hydraulic press, then a die attached to a vertical plunger comes down and turns over a flange on the cut end of the sample, this combines a flattening, crushing-down, and flange test in one. As this 1 has the utmost assurance that the material is of uniformly satisfactory quality. Tubes which fail to stand this test, on account of imperfect welding, are given another run through the furnace and rewelded, and are again subjected to the same test on the ends. Other physical tests are described in Standard Specifications for Locomotive Boiler Tubes, given on pages 99 to 102. 3. Our research department is continually testing and experimenting with the material for locomotive boiler tubes; this being the most severe service to which tubes are put, it is naturally the branch of the business to which we give most attention. To this end, tests of the safe ending quality are made on each lot; roller expander tests in the flue sheet, to determine the power of the material to withstand repeated working in the flue sheet without developing brittleness, are also made from time to time. Improvements in this line are reflected in the product designed for other purposes, where the demands of service are not so rigorous. SHELBY SEAMLESS STEEL TUBES Methods of Manufacture. The process employed in the manufacture of Shelby Seamless Tubes in our mill may be classified as follows: A. Tubes made from solid round billets.. B. Tubes made from steel plates. (a) Hot finish. (b) Cold finish. S (a) Hot finish. Class A includes by far the larger percentage of seamless tubes. The preliminary operations are the same for hot and cold-finished tubes made from solid round billets. The steel, of a special quality, made by the basic open-hearth process, is rolled into rounds approximating in diameter that of the finished tube; these are cut to suitable length to contain sufficient steel for a required length tube, then heated to a soft plastic state and pierced. Before heating these billets a hole is drilled in the center of one end, so that the piercing point may be started accurately in the center of the billet, thereby minimizing, so far as possible, the variations of thickness in the wall. There results from this operation a rather rough, thick-walled seamless tube, retaining on its surface evidence of the manipulation required to work the hot billet into this shape. The roughly pierced tube is now transferred, without loss of time and without reheating, to a rolling mill, where it is passed between rolls having semicircular grooves between which various sizes of mandrels are placed, and are supported in this position on the ends of stiff bars. By repeatedly passing the rough tube through these rolls and over mandrels, the steel is gradually elongated and the walls proportionately reduced in gage. Hot-finished Tubes are taken direct from the rolling mill while still retaining sufficient heat, and passed through a reeling machine of special design, which further slightly reduces the gage. The tube is straight Cold-finished Tubes. Where cold finish is required, the ends of the tubes after they leave the rolling mill are reduced, so that they may be firmly caught by the heavy tongs of the drawbench. They are first immersed in hot dilute acid to remove all scale outside and inside, so that a smooth, even surface may result from the cold drawing which follows. A mandrel is held in position by a long bar which lies inside the tube, and holds the mandrel just even with the die while the tube is being drawn. All tubes, except those having an inside diameter smaller than six-tenths of the outside diameter or smaller than 1⁄2 inch, are drawn over mandrels varying in diameter until the required diameter and thickness are obtained. The drawing operation hardens the steel, so that it is usually necessary to anneal the tube after each pass to restore its ductility, after which it is necessary to again put it through the acid pickling bath to remove the oxide-of-iron scale from the surface. After the last drawing operation the hammered points are cut off, and the tube is ready for testing and final inspection. Tubes Made from Steel Plates. As in the case of tubes made from round billets, these may be hot or cold finished, according to requirements. Hot-finished tubes are not as smooth as those cold drawn, hence, when it is necessary to produce a tube with smooth walls, it is given two or three cold passes, each operation being preceded by annealing and pickling. The "cupping" process is used in making seamless tubes over 51⁄2 inches outside diameter. Plates of the best-quality basic open-hearth steel of the required thickness are trimmed into circular shape and heated to a bright redness, then pressed roughly into the shape of a cup. This is re peated three or four times, reheating between each operation, and using smaller dies and punches as the process proceeds, until the cup has the shape of a cylinder closed at one end. The piece is then taken to the drawbench, where it is further elongated and reduced in gage by forcing through dies of successively decreasing diameter. Where a number of drawings are required, the piece is reheated before each draw. Finally the closed end, or head, is cut off and the tube cut to length. Carbonic Acid Cylinders. These are made from specially selected steel plates (see cylinder specifications). The preliminary operations in the making of these cylinders are as above described, except that the head is not cut off, and the other or open end is swaged down to receive a head. Materials. Three principal classes of material are used in the manufacture of seamless steel tubes, namely: all of which are of special quality as before stated. In addition to these materials, such as chrome-vanadium steels, higher-carbon steels, etc. The physical qualities of all these materials vary with the heat treatment, especially after the cold-drawing operation, which hardens the tube. The .17%-carbon steel tubes are suitable for boiler tubes and other purposes requiring great ductility; the .35%-carbon steel tubes are suitable for purposes in which higher elastic limits and ultimate strengths are required; and the 32% nickel-steel tubes are suitable for purposes requiring ductility combined with high elastic limits and ultimate strengths. Hot-finished tubes are not given any further heat treatment after leaving the hot mills. Cold-drawn tubes, however, are given regular heat treatments, which consist of either a soft anneal or a hard (finish) anneal, while for special purposes the heat treatment is varied to give properties suited to the purpose for which the tubes are to be used. The average chemical and physical qualities of the three main classes of materials, when same are given the regular heat treatments after the final cold drawing, are shown in the following table. *Foot-pounds Energy Absorbed under Impact, 6.97. (Material of this temper is of the maximum strength, with but slight ductility. The surface is bright and free from scale. Material of this temper is usually furnished for hose poles, cream separator bowls, etc.) *The impact test is made on a machine of special design, constructed as follows: A pendulum with a light rigid frame system and a heavy lower part is hung on roller bearings; these are supported in a frame of sheet iron, attached to a heavy cast iron base. The pendulum is always dropped from a fixed height; in swinging, it moves before it a pointer which records the maximum height to which the pendulum swung. In making a test, the specimen to be tested is clamped firmly in the base of the machine; it is placed so that it will be struck by the pendulum at the lowest point in the swing. The test piece is 516 inch 16 inch X 24 inches long, with a 60° notch cut 16 inch deep, 15% inches from the end of the piece. When the test piece is firmly clamped in the base, the pendulum is suddenly released and, when striking the test piece, it is checked a certain amount depending on the toughness of the test piece. The height of the swing after hitting the test piece is recorded by the pointer. Knowing the weight of the pendulum, the height of the free swing and the height of the swing after striking the test piece, it is possible to calculate the |