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. [Illustration: PLATES CALLED “SKELP” ARE FIRST ROLLED ] The pipe now goes through what are known as cross rolls, the axes of which are somewhere near parallel with the axis of the pipe. In these the pipe is rapidly spun around, surface-cleaned and straightened. Going up a cooling incline it goes to tables where the ends are cut off and the product inspected. A very important part of the inspection is the hydrostatic or water test. One at a time the pieces are tightly fitted in between two water-tight caps, water is turned into the pipe and gradually brought up to the testing pressure of 600 pounds or more per square inch according to specifications. [Illustration: CHARGING SKELP INTO THE HEATING FURNACE ] [Illustration: DRAWING BUTT-WELD PIPE ] Pipes of diameters between ⅛″ and 3″ are usually made by the butt-weld process. Lap-Welded Pipes Pipes larger than 3″, and boiler tubes or other particularly high grade welded tubes of 2″ and over are usually “lap-welded.” This process gives a considerably more reliable product than does the butt-welding process, for reasons which are readily seen. [Illustration: HOW LAP-WELD PIPES ARE MADE ] [Illustration: BENT SKELP FOR LAP-WELDING BEING CHARGED INTO FURNACE ] Skelp for lap-welding is rolled in just the same way as is skelp for butt-welding except that the edges are “scarfed” or decidedly beveled so that the two edges can make a considerable lap without increase of thickness of that part of the wall. These pieces of skelp are charged into the heating furnace just as occurred in the butt-weld process and, after coming to a white heat, they are drawn through a sort of bell or die which curves them so that one edge considerably overlaps the other. Back they go into the furnace to regain any heat that has been lost, for, to weld properly, the skelp must be hot enough that any scale which had covered it drips off. [Illustration: THE LAP-WELDING ROLLS WITH MANDREL IN POSITION ]