c) Vertical - On the wall d) Horizontal - On the wall Fig. 9 Different weld positions 7.0 TYPES OF JOINTS There are five basic types of common joints. They are Butt joint Lap joint T joint Corner joint, and Edge joint Each joint is suitable for a specific situation. The choice of the joint for a particular job depends on the size and shape of the members to be welded at the joint, the type of loading, area available for welding at the joint and relative cost of various types of welds. 7.1 Butt Joint Fig. 10 Typical butt joint
Butt joints are used to join the ends of flat plates of nearly equal thickness. A typical butt joint is shown in Fig. 10. This joint avoids eccentric transfer of force at the connection. It is preferable to have full penetration of welds at the butt joints so that the joint is fully efficient. The size of connection is quite small and hence is very economical. It is aesthetical to look at. Face reinforcement (weld beyond the surface) is normally provided in Butt joints. This increases the efficiency of the joint and ensures that depth of weld is at least equal to the thickness of the plate. 7.2 Lap Joint Fig. 11 Typical lap joint Lap joints are easy to fit and join any two members. A typical lap joint is shown in Fig. 11. It is the most commonly used joint. It does not require any special preparation. Lap joints utilize fillet welds. They are well suited for shop and field welding. Lap joints can accommodate minor errors in fabrication and minor adjustment in length. The main advantage of lap joints is that it can join plates with different thicknesses without any difficulty (Fig. 12). The main disadvantage of this joint is that it introduces eccentric transfer of loads at the connection. Fig. 12 Lap joint with plates of different thickness
7.3 T Joints Fig. 13 Typical T - joint A T-joint is usually used to fabricate built-up sections from simple members. A typical T-shaped joint is shown in Fig. 13. Some of the commonly used built-up shapes where T-joints are seen are I-sections, Plate girders, Hangers, Brackets, and Stiffeners. The members in the built-up sections are joined by means of fillet welds or groove welds. 7.4 Corner Joint Corner joints are normally seen in built - up rectangular box sections. A typical corner joint is shown in Fig. 14. They are generally seen at places which are subjected to high torsional moments. Fig. 14 Typical corner joint
Corner joints are seen in the built - up rectangular box sections. A typical corner joint is shown in Fig. 14. They are commonly seen at places which are subjected to high torsional moments. 7.5 Edge Joint Fig. 15 Typical corner joint Edge joints are generally not used in structural applications. They are used to keep two or more plates in position in a given plane. A typical edge joint is shown in Fig. 15. 8.0 WELD SYMBOL AND WELDING SYMBOL A weld symbol is a symbol which indicates the type of weld to be adopted to joint the metal pieces. However, a welding symbol is a concise way of describing all particular information related to the weld on drawings. 8.1 Weld Symbol Weld symbol is unique for each specific type of weld. Hence the weld symbol used is different for fillet, groove, plug, and slot welds. 8.1.1 Basic Weld Symbols The basic weld symbols for the commonly used welds are shown in Table 3.
Table 3 Basic weld symbols Weld symbol is only a part of the information regarding the welding operation to be performed at a joint. As indicated in Table 3, whenever a weld symbol consists of both vertical and inclined legs, the vertical is always drawn towards the left side of the inclined line. 8.2 Welding Symbol The welding symbol contains all the information necessary in connection with a welding operation. It also includes the type of weld, where welds are to be located, the type of joint to be used, and the size and amount of weld metal to be deposited in the joint. The symbols used are standardized by the various codes of practice so that the entire information can be concisely represented in a drawing. The basic welding symbol comprises of three parts, namely a reference line an arrow, and a tail
Apart from this there are also supplementary welding symbols to represent Dimensions and other data Supplementary symbols Finish symbols Specification, process or other reference 8.2.1Basic Welding Symbols Fig. 16 Basic welding symbols Reference Line The reference line is always drawn horizontally. It is mandatory and forms the foundation of a welding symbol. All information with respect to the welding process is to be indicated around this line. Arrow The arrow line is present at one end of the reference line. It simply connects one end of the reference line to the joint or area to be welded. The direction of the arrow has no bearing on the significance of the reference line. Some of the possible types of arrows used in the welding symbol are shown in Fig. 17.
Fig. 17 Different types of arrows used in welding symbol Tail The tail is shown on the other end (away from arrow end) of the reference line. It is not mandatory. The tail is used to specify a certain welding process. It is used only when necessary. It is used to mention some special characteristic of the weld like type of electrode, some type of reference or specification, welding or cutting process, procedures or other supplementary information. If additional information is not needed, then the tail will be omitted. The representation of tai with additional information is shown in Fig. 18. Fig. 18 Representation of tail with additional information 8.2.2 Interpretation of Symbols Fillet weld on arrow side Symbol Meaning
Fig. 19 Fillet weld, Arrow side Fillet weld on other side Symbol Meaning Fig. 20 Fillet weld, Other side Fillet weld on both sides Symbol Meaning Fig. 21 Fillet weld, Both sides Bevel edge Symbol Meaning
The symbol indicates that one edge of a joint is to be beveled. The arrow should points towards the member to be beveled. Hence, the arrow should show a definite break so that the member to be beveled can be clearly identified. Fig. 22 Bevel edge 8.2.3 Standard Location of Elements of a Welding Symbol The standard location of various elements of a welding symbol to be indicated in drawing is summarized below. Fig. 23 Standard location of welding symbols 8.3 Supplementary Symbols
There are some supplementary weld symbols used in addition to the basic weld symbols which are indicated in section 8.1. These include Finish and contour symbols, All round weld, and Field or site weld which are shown in Table 4. Table 4 Supplementary weld symbols 8.3.1 Finish and contour symbols Finish symbol shows the method of finish to be carried out to a weld. Generally, the finish of welding is either by chipping (C) or by machining (M) or by grinding (G). Contour symbols are used with weld symbols to show how the face of the weld is to be formed. The face of the weld will be either flat, convex or concave as shown in Table 4. 8.3.2 All round weld Fig. 24 Typical representation of all round weld