426 Modern Welding Copyright Goodheart-Willcox Co., Inc. Bevel angles can be cut at the same time the metal is being cut to size and shape. A bevel can also be cut as a separate operation. The technique used to cut a bevel is similar to the technique used to cut thick metal. How- ever, the torch is held at an angle to the base metal, and the cut is generally made at an existing edge of the metal. It is important to obtain a high-quality cut when making the bevel. This minimizes any further plate preparation and ensures a good fi t-up of the joint to be welded. 15.5.6 Cutting Pipe or Tubing Oxyfuel gas cutting torches are commonly used to prepare pipe for joining by welding. Cutting torches are especially useful for preparing pipe connections other than end-to-end connections. Examples are T, K, and Y connections. These are discussed in Chapter 23, Pipe and Tube Welding. Cutting torches are also often used to bevel the edges of thick pipe to create a bevel- groove or V-groove joint. A standard pipe bevel angle commonly made is 37.5°. 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 (intersecting the pipe at a single point) to the inner circumference of the pipe. See Figure 15-30. This prevents cutting through both sides of the pipe at once. Attempting to cut through the two thicknesses of the pipe simultaneously will result in a poor cut. With a pipe diameter of approximately 4″ (100 mm) or larger, the torch tip can be kept perpendicular to the pipe surface while cutting, without burning through the other side. See Figure 15-31. 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. Pipe can be cut to length with a square end, no bevel, by cutting at 90° to the pipe surface. Pipes can be cut to length and beveled with the same cut. To pro- duce a bevel cut, point the torch toward the open end of the pipe. Roll the torch to produce the desired bevel angle. With skill, a welder will produce a clean bevel with no slag on the cut surface. Oxyfuel gas cutting machines that revolve the torch around the pipe pro- duce excellent beveled edges. Figure 15-32 shows how to use a cutting torch to bevel or chamfer the end of a pipe. Remember that for cutting pipe, it is the thickness of the pipe wall rather than the diameter of the pipe that determines the size of the cutting torch tip. All relevant welding codes and procedures must be followed whenever pipe is cut for structural or pressure vessel applications. Thermadyne Industries, Inc. Figure 15-31. The cutting torch tip can be kept perpendicular when cutting pipe with a diameter greater than 4″ (100 mm). 45° Goodheart-Willcox Publisher Figure 15-32. A cutting torch being used to cut a bevel on a steel pipe. A B Goodheart-Willcox Publisher Figure 15-30. Proper angles for cutting small-diameter pipe. A—The red lines are tangent to the circle. If the lines were extended, they would still intersect the circle at a single point. B—The proper torch angle for cutting small-diameter pipe. Note that the kerf marks are roughly tangent to the inner diameter of the pipe.