The first patents for the making of welded pipe as we know it were taken out in 1824 and 1825, the latter for the butt-welding method of pulling a narrow iron plate, called “skelp,” through a bell-shaped orifice which curled it and welded the edges together very much as is done to-day by this process.
Our modern pipe of both butt-weld and lap-weld varieties is manufactured either from wrought iron or from soft steel.
The Butt-Weld Process
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Early Water Pipes
How Butt-weld Pipes Are Made
From the double refined puddled iron, in the case of wrought iron, or from billets of soft Bessemer or open-hearth steel, long narrow plates are rolled. The width and thickness of these plates, which are known as “skelps,” are exactly such as will give pipe of the desired diameter and gauge. In order that the weld may be solid all along, the skelp as it leaves the rolls has edges not exactly square but very slightly beveled, so that the surface which is to form the interior of the pipe is slightly narrower than the other.
After trimming the pieces of skelp so that each has one end with a sort of point where the tongs are to take hold, they are laid side by side in a heating furnace and left there until they have become white-hot.
Just in front of the furnace is the “bell,” with a second and slightly smaller one in front. With strong tongs the workman reaches into the furnace and fastens onto the pointed end of a piece of the white-hot skelp. Hooking the handle of his tongs into the draw chain the skelp is drawn through the first and second bell, the first bending it almost into tube shape, the second completing the operation and pressing together the edges of the plate in the top of the bell so tightly that they weld.