WRINKLE BENDS

It may seem odd that after describing precautions necessary to keep a bend free of wrinkles, we next describe a method which deliberately produces wrinkles as a means of bending the pipe. Nevertheless, you will find the wrinkle-bending technique a simple and direct method of bending pipe, and perhaps in man y pipe-bending situations, the only convenient method. This would particularly be the case if no bending slab were available or if time considerations did not permit the rather lengthy sand-packing process.

Basically, wrinkle bending consists of a simple heating operation in which a section of the pipe is heated by a gas welding torch. When the metal becomes plastic (bright red color), the pipe is bent SLIGHTLY, either by hand or by means of tackle rigged for that purpose. The unheated portion forms the heel (outside) of the bend, while the wrinkle is formed at the throat (inside) of the bend due to compression.

It should be understood that the pipe should not be bent through very large angles (12 degrees being considered the maximum for one wrinkle) to avoid the danger of the pipe buckling. The procedure in making a large bend is to make several wrinkles, one at a time. If, for example, you want to produce a bend of 90 degrees, a minimum of eight separate wrinkles could be made. Figure 13-65 shows a 90-degree bend made with ten separate wrinkles. The formula to determine the number of wrinkles is to divide the degrees per wrinkle required into the degrees of the bend required.

Figure 3-65.-90-degree bend made with ten separate wrinkles.

Wrinkle bending has been successful on pipe of more than 20 inches in diameter. Experience has shown that, for 7-inch-diameter pipe and over, more complete and even heating is accomplished using two welding torches, rather than one. In any event, the heating procedure is the same-the torch or torches being used to heat a strip approximately two thirds of the circumference of the pipe (fig. 3-66). The heated strip need not be very wide (2 to 3 inches, or 5.08 to 7.62 cm, is usually sufficient) since the bend will only be through 12 degrees at most. The heated portion, as we have noted, is the part which will compress to become the inside of the bend. The portion which is not heated directly will form the outside of the bend.

The technique most often used to bend the pipe, once it has been heated, is simple and straightforward. The pipe is merely lifted up by hand (or by tackle), while the other end is held firmly in position.

Figure 3-66.-Part of pipe heated before wrinkle bending.

Chapter 4

FIBER LINE

Starting with this chapter, we explore another major area of steelworking skills-the erection and assembly of steel structure. Steelworkers require tools to hoist and maneuver the steel members into place to erect a structure of any magnitude. These hoisting tools range from uncomplicated devices, such as tripods and gin poles, to more complex mechanisms, such as cranes and motor-powered derricks. Whatever the case, one of the most important components of these hoisting mechanisms is the fiber line or wire rope that must be attached to and hold the load to be hoisted and maneuvered. Before you, as a Steelworker, can become skilled in the supervision of hoisting devices, you must first understand the use and maintenance of fiber line and wire rope.

FIBER LINE

This chapter and the next are designed to familiarize you with the different types of fiber line and wire rope commonly used by Steelworkers. We also discuss knots, bends, hitches, clips, and fittings and describe how they are used. Other topics discussed include the handling and care of fiber line and wire rope, making splices in fiber line, and methods of determining safe working loads.

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