PARTS OF JOINTS
While there are many variations of joints, the parts of the joint are described by standard terms. The root of a joint is that portion of the joint where the metals are closest to each other. As shown in figure 3-7, the root may be a point, a line, or an area, when viewed in cross section. A groove (fig. 3-8) is an opening or space provided between the edges of the metal parts to be welded. The groove face is that surface of a metal part included in the groove, as shown in figure 3-8, view A. A given joint may have a root face or a root edge. The root face, also shown in view A, is the portion of the prepared edge of a part to be joined by a groove weld that has not been grooved. As you can see, the root face has relatively small dimensions. The root edge is basically a root face of zero width, as shown in view B. As you can see in views C and D of the illustration, the groove face and the root face are the same metal surfaces in some joints.
The specified requirements for a particular joint are expressed in such terms as bevel angle, groove angle, groove radius, and root opening. A brief description of each term is shown in figure 3-9.
The bevel angle is the angle formed between the prepared edge of a member and a plane perpendicular to the surface of the member.
The groove angle is the total angle of the groove between the parts to be joined. For example, if the edge of each of two plates were beveled to an angle of 30 degrees, the groove angle would be 60 degrees. This is
Figure3-10.-Root penetration and joint penetration of welds.
Figure 3-11.-Weld reinforcement.
often referred to as the "included angle" between the parts to be joined by agroove weld.
The groove radius is the radius used to form the shape of a J- or U-groove weld joint. It is used only for special groove joint designs.
The root opening refers to the separation between the parts to be joined at the root of the joint. It is sometimes called the "root gap."
To determine the bevel angle, groove angle, and root opening for a joint, you must consider the thickness of the weld material, the type of joint to be made, and the welding process to be used. As a general rule, gas welding requires a larger groove angle than manual metal-arc welding.
The root opening is usually governed by the diameter of the filler material. This, in turn, depends on the thickness of the base metal and the welding position.
Figure 3-12.-Simple weld bead.
Having an adequate root opening is essential for root penetration.
Root penetration and joint penetration of welds are shown in figure 3-10. Root penetration refers to the depth that a weld extends into the root of the joint. Root penetration is measured on the center line of the root cross section. Joint penetration refers to the minimum depth that a groove (or a flange) weld extends from its face into a joint, exclusive of weld reinforcement. As you can see in the figure, the terms, root penetration and joint penetration, often refer to the same dimension. This is the case in views A, C, and E of the illustration. View B, however, shows the difference between root penetration and joint penetration. View D shows joint penetration only. Weld reinforcement is a term used to describe weld metal in excess of the metal necessary to fill a joint. (See fig. 3-11.)
Figure 3-13.-Standard groove welds.