Welding Complicated Pipe Joints
The principles of pipe welding have been treated in the last six chapters. Much emphasis has been placed on small, but important, details, such as the preparation of the pipe joint, striking the arc, the arc length, the electrode angle, and controlling the molten pool of metal. Procedures for welding root beads, intermediate layers, and cover passes have also been explained in detail. These same principles and procedures are used when welding more complicated pipe joints, with some slight differences.
Welding Variations for Complicated Pipe Joints
In this chapter, emphasis will be placed on slight variations in the procedures, which are required for welding more complicated pipe joints, as those illustrated in Fig. 10-1. This does not mean that details such as the preparation of the pipe joint, striking the arc, etc., can be neglected. On the contrary, they are just as important as before, and if the weld is to be sound throughout, they must be performed in a craftsmanlike manner.
Root Beads. The foundation of any successful pipe weld is the root bead. When welding more complicated pipe joints the same holds true and procedures are exactly the same as those described in previous chapters.
The welder must determine whether to weld the root bead uphill or downhill. Usually, uphill welding is preferred. By this method it is easier to control the weld metal and to obtain a good weld, especially when consideration is given to the various directions in which the weld must be deposited on some of the pipe joints. Moreover, root beads deposited by the downhill method must be ground and grinding certain parts of some of the more complicated weld joints, such as in sharp corners, is difficult.
Courtesy of (he Hobart Brothers Co. Fig. і0-1 - A variety of perfectly welded pipe joints.
When welding a root bead on a complicated pipe joint, the welder must also decide in advance what procedure to use. Usually, he
should start to weld at the lowest part of the pipe joint. If this requires overhead welding, the electrode should be advanced at a slow, steady pace, with or without whipping the electrode. When the joint requires welding in the vertical uphill or in the flat position, the whipping procedure is used to control the puddle. Whipping is also used to weld in the horizontal, or nearly horizontal, welding position; here the arc length must be shortened somewhat.
This is but a brief review of root-bead welding. For more details, the reader should refer to previous chapters. In the remainder of this chapter, root bead welding is not discussed in detail; however, when actually welding a more complicated weld joint this part of the weld must be given as much attention as welding the filler layers. Failure to do so will most certainly result in a defective pipe joint.
Intermediate and Cover Passes. There are also great similarities between the procedures already described and those used to weld the intermediate and cover layers on more complicated joints. A welder who has mastered the principles and procedures treated up to this point should have no great difficulty in learning how to weld the filler passes on the pipe joints to be treated further on.
The intermediate and cover layers on the more complicated pipe joints might be called weave layers because a weave is usually necessary to control the pool of molten metal and to fill the weld joint with sound metal. The weaves to be described in the following pages have all beer, used to make high-quality weld joints. Other techniques have also been used, but they are not likely to produce better welds. The beginner should first master the procedures described in this chapter; then, if he chooses, he can experiment with other techniques.
There are exceptions when the following procedures should not be used. These exceptions will be treated at the end of this chapter. However, when these procedures are used, the welder must not neglect the following details;
1. Remove the slag from the previous layers and clean the weld joint thoroughly.
2. Supply adequate heat input by having the correct current setting for the weld to be made.
3. Strike the arc in the joint, allow it to stabilize, then allow time for the gaseous shield to form before the arc is shortened; continue to maintain the correct arc length at all times.
4. Maintain the correct electrode angle.
5. Manipulate the electrode smoothly and maintain the correct speed of travel
Some of the joints will require welding in two or three directions. In such cases the welder must be alert to change the electrode manipulation and angle as required. He determines when these changes are required by the behavior of the molten pool of metal. He must avoid undercuts, sagging, and a bead of poor appearance.
The recommended procedures to follow are described by illustrations which show the weave pattern to be used as in Fig. 10-2. In studying the illustrations of the weave pattern on the following pages, the lines that describe these patterns have the following meaning:
1. Heavy lines indicate a normal speed of travel, where filler metal is, therefore, deposited.
2. Light lines indicate a faster speed of travel to avoid any regular deposit of filler metal and, at the same time, to temporarily remove the arc from the puddle in order to cool the molten metal and prevent it from sagging.
Fig. 10-2. Designation of weave pattern symbols. Heavy lines: normal welding speed; light lines: faster speed of travel; dots: pauses.
3. Dots indicate a pause in the movement of the electrode in order to heat the metal and to deposit filler metal. Often this is done to prevent undercutting.