Cutting pipe is not much different than cutting structural shapes, except that you must always keep in mind that the cut will either be radial or miter. The gas cutting torch is used to cut pipe fittings for welding. Procedures relating to the use of the cutting torch are given in volume 1, chapter 4. The torch maybe hand operated, or it maybe mounted on a mechanical device for more accurate control.
Cutting machines may be used to prepare many fittings without the use of templates. These machines cut and bevel the pipe in one operation-the bevel extending for the full pipe wall thickness. When the pipe is cut by hand, beveling is done as a second operation.
For many types of welded fittings, a RADIAL cut is required before beveling. Radial cutting simply means that the cutting torch is held so it is perpendicular to the interior center line at all times. In other words, the cutting orifice always forms a continuation of a radius of the pipe, making the cut edge square with the pipe wall at every point. Figure 3-59 shows radial cutting. Except in the case of the blunt bull plug, for which the radial cut provides the proper vee, the radial cut should be followed by a beveling cut for pipe with 3/1 6 inch (4.8 mm) or more wall thickness.
In MITER cutting the torch tip is held so that the entire cut surface is in the same plane. The miter cut is followed by a beveling cut, leaving a 1/32- to 1/16-inch (.8 to 1.6-mm) nose at the inner wall. Figure 3-60 shows miter cutting.
Figure 3-60. - Miter cutting.
Any piping system of consequence will have bends in it. When fabricating pipe for such a system, you can make bends by a variety of methods, either hot or cold, and either manual] y or on a power-bending machine. Cold bends in pipe are usually made on a bending machine. Various types of equipment are available, ranging from portable handsets to large hydraulically driven machines that can cold bend pipe up to 16 inches (40.64 cm) in diameter. You will be concerned primarily with hot bending techniques, using a bending slab or using a method known as wrinkle bending.
Whatever method you use to bend pipe, you should normally have some pattern that represents the desired shape of the bend. Templates made from wire or small, flexible tubing can be invaluable in preparing new installations as well as in repair work, When properly made, they will provide an exact guide to the bend desired.
One of the simple types of bend template is the center line template. A centerline template is made to
Figure 3-59. - Radial cutting.Continue Reading