Wrought-iron pipes appear to have been first employed to convey illuminating gas, and this remains one of the most common uses, the carrying of steam and water being others. At first they were made by hand, the plates being bent and the seams welded, a few inches at a time. The develop ment of steam engineering, however, created a demand for larger and stronger pipes, in the production of which new processes of manu facture employing special machinery have been introduced and developed to a high state of perfection. The wrought-iron pipe and tube Industry was one of the last to discard puddled iron in favor of Bessemer steel. The advan tages of increased strength and lower cost, to be obtained by the use of steel, had been fully realized for some time, but the difficulty of mak ing lap-welded and butt-welded steel pipes, hav ing the same strength in the weld as in the body of the pipe, prevented its adoption.
Methods of These difficul ties, however, have been overcome by improved methods of production in materials and ma chinery in pipe making. The general process of manufacture is as follows: A carefully selected grade of cast iron, together with the proper quantities of coke and limestone, are melted down in the cupolas of a blast furnace, drawn off and placed in the Bessemer converters, where it is heated until practically all of the carbon in the cast iron has been burned out. The metal is then poured into casting ladles, into which an amount of ferromanganese is also added, sufficient to give the proper proportion of manganese and carbon. The resulting metal is a mild steel of a very reliable welding quality. The cast ingots are then placed in the soaking pit and raised to a white heat. From the soak ing pit they are picked out by overhead cranes and rolled down into the blooms of the bloom ing mill. This mill is of massive construction and is driven by horizontal reversing engines. It consists of a set of reversible mill rolls, with a long table of rollers on each side. The action of the rollers draws the ingot quickly into the rolls and as soon as it has passed through, the engines are reversed, the rolls are brought a little closer together by a pair of screws set in the standards and the ingot is again reduced in thickness. This operation is repeated until it has been brought down to the desired section, when it is sheared into short lengths, called slabs and billets. These are re heated and passed through a continuous mill, consisting of a large number of rolls in pairs, placed one beyond the other at increasing in tervals. As the billets or slabs are carried through each successive pair of rolls, they are reduced in thickness and increased in length, until they issue from the last pair of rolls in the form of long narrow plates, known as skelp. They vary in width from a few inches
Ur to eight feet. In the narrower strips, used for smaller pipes, the width is sufficiently uni form to dispense with the necessity of trimming up with shears, but the skelp for large pipes has to be carefully trimmed to the right di mensions. In general, all wrought-iron or steel pipes may be divided into two classes — lap welded, ranging from PA to 30 inches and butt welded, from one-third to one and one-fourth inches in diameter. In lap-welding, the plate is first laid upon a traveling table and has its edges scarfed or beveled. It is then heated in a bending furnace and rolled up into the form of a pipe, with the beveled edges overlapping. This partially made pipe (known also as skelp) is brought up to a welding heat in a furnace and then passed through the concave welding rolls between which a ball-shaped mandrel, the diameter of which is equal to that of the pipe, is held in position by a long bar. As the skelp passes through the rolls, the overlapping edges are squeezed together between the rolls and the mandrel into a more or less perfect weld. The rough pipe is then passed through the siz ing rolls and brought to the exact diameter re quired; then through the cross-straightening rolls and made perfectly straight ; then rolled on a cooling table while cooling, to nrevent warp ing and finally forced through the dies of the straightening machine by hydraulic pressure. The ends are then trimmed and threaded and after being screwed into the couplings, it is tested in a hydraulic testing machine. The smaller sizes under pressures ranging from 600 to 1,500 pounds and the larger sizes from 500 to 750 pounds to the square inch. Oil-well piping is tested under pressures as high as 2,500 pounds to the square inch. In butt-welding, the edges of the plate are left square. The skelp is heated in a furnace and raised to a welding heat. It is then drawn through a hell-shaped die, the diameter of which is a little less than that of the skelp. The pressure thus induced soueezes the edges together and makes a perfect weld. The smaller pipes are usually fitted with screwed flanges and couplings. In the larger pipes the flange is formed out of a bar of steel, bored out and faced on the inner face, a half-inch fillet being left on the inner edge. The end of the pipe is swaged down slightly, the flange pushed over it and the edge of the pipe headed over to hold the flange in place while it is in the furnace. When it has reached a welding heat, it is placed on a concave anvil, stepped to receive both pipe and flange and revolved axially under the blows of the hammer which quickly effect a weld. Flanges have been welded on pipes over 30 inches in diameter, with satisfactory results.