424 Modern Welding 14.6.4 Cutting Pipe or Tubing One of the most common uses of oxyfuel gas cutting torches is to prepare pipe for joining by welding. See Chapter 22 for more pipe welding instructions. Cutting torches are especially useful for preparing odd-shaped joints on the job. They are also often used to chamfer the edges of thick pipe to create a bevel or V-groove joint. The exact procedure to follow when cutting pipe depends on the pipe’s diameter. For small-diameter pipe, it is best to keep the tip almost tangent (inter- secting the pipe at a single point) to the inner circum- ference of the pipe. See Figure 14-31. This prevents cutting through both sides of the pipe at once. Attempting to cut through the two thicknesses of the pipe simultaneously usually results in a poor cut. With a pipe diameter of approximately 4″ (102mm) or larger, it is possible to keep the torch tip perpendic- ular to the pipe surface while cutting, without burning through the other side. See Figure 14-32. Of the two methods, the perpendicular position permits a cleaner and straighter cut. If the welder’s helper rotates the pipe as it is being cut, a very clean cut can be obtained. If the pipe is being chamfered, most welders start the cut at the extreme edge of the pipe and then cut back to the marked chamfer ring. The cutting operation can be cut to length and chamfered with the same cut. Point the torch toward the end of the pipe when chamfering pipe by hand. This procedure provides a clean chamfer, permits more accurate cutting, and should not leave any excess oxide clinging to the pipe when the cut is completed. Cutting machines that revolve the torch around the pipe produce excellent chamfered edges. Figure 14-33 shows how to use a cutting torch to bevel or chamfer the end of the pipe. Remember that when cutting pipe, it is not the diameter of the pipe that determines the size of the cutting torch tip. Figure 14-31. Proper angles for cutting small-diameter pipe. A—The red lines are tangent to the circle. Note that if the lines were extended, they would still intersect the circle at a single point. B—Proper torch angle for cutting small-diameter pipe. Note that the kerf marks are roughly tangent to the inner diameter of the pipe. A B Figure 14-32. The cutting torch tip can be kept perpendicular as shown when cutting pipe with a diameter greater than 4″ (100mm). (Thermadyne Industries, Inc.)