Thin-wall pipes are categorized as having a wall thickness less than 5/ie inch. The diameter of thin-wall pipes may be as small as I inch and as large as 42 inches, or larger, such as that used for cross-country pipelines. When the pipeline is horizontal, or the pipes are in the 5G position, either the […]

The shielded metal-arc welding process has been widely used for many years to weld pipe material It is still used, even in the most modem industries. The process is used with various types of alloy pipe materials in constructing power plants, oil refineries, chemical plants, nuclear power plants, and oil and gas transmission lines. Specifically […]

Multilayer welds are used to weld all thick-wall and most thin­wall pipes. The multilayer weld is more ductile and free from defects than a large single-layer weld would be. A multilayer weld is also easier to make because it is more difficult to control the large puddle of molten metal of a single-layer weld. Since […]

Gas tungsten arc welding has been used to great advantage in all kinds of pipe welding applications. Besides affording the welder excellent visibility due to the lack of smoke and spatter, there is no porosity due to slag entrapment, and the deposits are essentially hydro- gen free. The GTAW process is particularly useful, due to […]

1. Pure tungsten 2. 1 or 2 percent thoriated tungsten 3. Zirconiated tungsten. Recommendations for the applications of the types of electrodes are provided in Table 6-1. Thoriated tungsten electrodes are used for most pipe welding applications, including mild steel pipe. The shape of the electrode tip has a marked influence on the contour, penetration, […]

In the literature of welding the Gas Tungsten Arc Welding pro­cess is usually shortened to GTAW. It is also sometimes called TIG (Tungsten Inert Gas) welding. When root beads of exceptional quality must be made, the GTAW process is very frequently used. Entire welds are seldom made by this process except in situations where unusually […]

A perfect root bead should be free from undercuts, porosity, incomplete fusion, insufficient penetration, and excessive penetra­tion (see Fig. 5-14). All of these defects can be avoided by learning and practicing the correct welding procedures. It should be kept in mind that these defects are the responsibility of the welder. Porosity cannot be blamed on […]

-WELL FUSED *SLIOHT CROWN END EVEN RIPPLE TOP SLIGHT CROWN BOTTOM Fig. 544. Weld quality inspection showing good weld and common welding COMMON WELDING MISTAKES POOR APPEARANCE 1. Wefding current too high 2. faulty joint preparation 3. Lack of arc control INSUFFICIENT PENETRATION t. Weidmg current too low 2. Travel speed too fast 3. Fk>Ot […]

The process of joining a bead, in this case the root bead, is called a tie-in. The previous weld may be a tack weld or it may be the first half of the root bead. In either case, the two welds must be brought together smoothly and without discontinuities. Making a tie-in requires extra care […]

With the keyhole and the puddle established and with the elec­trode held at the correct angle, the electrode is advanced around the bottom of the pipe. There is no back-and-forth motion across the pipe joint, only a linear, or straight, movement along the joint in the direction of welding. The movement of the electrode should […]