Т-Joint with intersection at the Side
Another common orientation at which T-joints must be welded is shown in Fig. 10-8. In this case, the weld must be made in three welding positions, namely: overhead, vertical uphill, and flat, in the order given. The overhead weld is made using a slanted “loop” weave while for the other two welding positions, a slant weave is used.
A Y-joint is illustrated in Fig. 10-9. The pipes are first joined together by a root bead after which the filler beads are added. Welding is done by working from the bottom toward the top of the joint. Three tie-ins must be made. One tie-in is made at the highest part of the joint and two are made at the sides of the joint (one on each side) at the point of intersection of the three pipes.
It is best not to start a bead at the point of intersection of the three pipes because the heat will be withdrawn more rapidly at this point than anywhere else. For this reason, one of the beads should be continuously welded past this part of the weld. This bead should be
deposited first. The bead below the other pipe then can be welded up to this point, where the tie-in is made.
This joint requires welding to be done in three basic welding positions. A slanted “loop” weave is used to weld in two places where overhead welding is required. The parts of the joint that require vertical uphill and flat welding are welded by using a slant weave, as shown in Fig. 10-9.
Portions of the pipe joints that require welding in the horizontal (2G) position, in some instances, should not be welded by using a weave. While the recommendations given in the preceding pages usually can be used, they must sometimes be modified when it is necessary to weld a bead in the 2G position.
When the weaving procedure cannot be used in the horizontal welding position, the weld is made by depositing a series of “stringer” beads in this portion of the joint. Stringer beads are deposited by moving the electrode at a slow, steady pace, with very little weaving. The situations where a weave pattern cannot be used in the 2G position are listed below:
1. When welding high-аІІоу pipe joints
2л When using low-hydrogen electrodes
3. When welding very heavy-wail pipe joints.
Using a wide weave pattern to weld in the horizontal position will momentarily expose the hot metal to the atmosphere. When welding pipe having a higher alloy content, this pattern will result in oxidation and porosity in the weld metal. Welding stringer beads provides better protection against oxidation and porosity as the gaseous shield will be maintained over the hot metal. Therefore, stringer beads instead of a weave should be used to deposit the bead when welding higher alloy pipe in the horizontal welding position.
The weld metal deposited by heavily-coated, low-hydrogen electrodes is very fluid and cools very slowly. When the deposit is in the horizontal welding position, it will tend to sag and entrap slag. Also, the temporary removal of the gaseous shield resulting from a wide weave pattern will cause the slowly cooling metal to absorb oxygen, forming oxides. For these reasons, stringer beads should be used to weld in the horizontal position when welding with low-hydrogen electrodes.
Heat will dissipate more rapidly and the molten metal will solidify more rapidly in thick-wall pipe than in thin-wall pipe. Moreover, more heat is required to melt the metal in thick-wall pipes because a larger amount of heat from the arc is lost to the walls of the pipe. To overcome this difficulty the current setting is increased to provide more heat input, which creates a larger pool of molten metal. In the horizontal welding position the large pool of molten metal will tend to sag and, if a wide weave is used, difficulty will be experienced in preventing cold lap and undercutting at the upper edge of the weld bead. Therefore, heavy-wall pipe should be welded with stringer beads when in the horizontal, or similar, positions.