WROUGHT-IRON PIPES. The earliest wrought iron pipes appear to have been made from an over-stock of gun barrels, early in the nine teenth century. The small end of one tube was screwed into the large end of the other. The pipes thus made were used to convey illuminat ing gas. The longitudinal joints were lap-welded. The increasing demand for wrought-iron gas pipe led to the adoption of butt-welded pipes of uniform size and thickness, united by sockets or couplings into which the ends of the pipe were screwed. Like the gun barrels, these pipes were welded by hand, a few inches at a time. In 1525 Cornelius Whitehouse invented a process of butt-welding which was, in its essential:. con tinued in use through the remainder of the cen tury. He first rounded up the iron plate, or skelp. then heated half the length of the pipe and drew it through two dies by means of a chain. The dies pressed the heated metal to °ether. This patent was bought by .James and John Russell. pipe manufacturers. one of whom had just patented a proves., of butt-welding by pressing the edges together, but in which only a few inches could be welded at a time.
With the development of steam engineering larger and stronger pipes were demanded. The Russells bent their energies to meeting this demand by improving on the old lap-welding process already described. This appears to have been about 1S35, but whgtever the (late, their process for lap-welding, like theirs for butt welding, involved the main principles still fol lowed. In the recent process of lap-welding pipe and tubes the strips or plates of metal are heat ed, have their edges beveled or scarfed by pass ing through rolls, and then drawn through a die and formed with edges overlapping, ready to be welded. The partly made pipe, or skelp. is now
heated a second time and welded by passing it through two rolls, the inner lop resting on a stationary mandrel, which corresponds to a blacksmith's anvil. Finally, the pipe thus made is straightened, threaded, screwed into a coup ling, and tested by means of water pressure. Butt-welded pipes are now made by drawing a heated plate. by means of tongs. through a conical-shaped die, thus pressing the edges so firmly together that they unite. The further steps in the process are the same as for lap welded pipe. Butt-welded wrought-iron pipe is made in small sizes, from to about 1 inch in diameter, and is tested at an internal pressure of 300 pounds per square inch. Lap-welded pipe is made in sizes from 1l or to 30 inches in diameter, and is often subjected to very high pressures.
Pipes are also drawn from hollow or cylin drical ingots formed by passing a heated round billet through diagonal rolls and over a mandrel. By reheating and rolling under pressure the ingot is finally brought down to the desired diameter and thickness. It is then annealed, pickled, and cold-drawn, to give it the desired finish. In the Mannesman process, invented in Europe, and patented in America in 1557, pipe is rolled from a solid, but heated, bar or rod by means of two tapering rolls and a mandrel.