GOPAL ENGINEERING WORKS
One method for reducing the mass of information contained in various documents, especially drawings, is through the use of symbols. This practice replaces written words and detailed graphic illustrations with specific symbols to convey the same information in an abbreviated manner. To provide continuity, the American Welding Society has developed a standard which describes the construction and interpretation of all types of welding and nondestructive testing symbols. This document AWS A2.4 Symbols for Welding and Nondestructive Testing, details all requirements relating to the use of these symbols.
Welding and nondestructive testing symbols can be thought of as a shorthand method for conveying information pertinent to these operations. While quite simple, this system provides a powerful method of describing detailed information. The designer can communicate a vast amount of information to fabrication and inspection personnel regarding numerous aspects of some welding project. Some of the information which can be described through the use of a welding or nondestructive testing symbol includes:
01 type of joint configuration
02 specific shape of weld preparation
03 type of weld
04 welding specification or procedure
05 relevant specification or procedure
06 location of weld
07 extent of welding
08 weld quality requirements
09 methods for verification of weld quality
10 weld sequencing
11 weld size
12 final weld configurations
13 methods of producing that configuration
As can be seen from this listing, the welding or testing symbol can be used effectively to provide a great deal of information. A key point is that the symbols must be properly used to be effective. Once the welding inspector understands how reverse to gaining sight as to what is actually required for that weld to be in compliance with the symbol. Therefore, the following discussion will be an attempt to take the inspector through the various steps associated with the construction of a welding or non destructive testing symbol
Elements of the welding symbol
A basic distinction which must be pointed out is the difference between the terms weld symbol and welding symbol. As stated in AWS A2.4, the weld symbol indicates the type of weld. The welding symbol is a method of representing the weld symbol on drawings, and includes supplementary information and consists of th4 following eight elements. Not all elements need be used unless required for clarity.
1 reference line (shown horizontally)
3 basic weld symbols
4 dimensions and other data
5 supplementary symbols
6 finish symbols
8 specification, process, or other references
figure 4.1 illustrates the standard locations of the various elements of a welding symbol.
Fig No. 4.1 standard location of elements of welding symbol
In the construction of a welding symbol, the primary element which is always included is the reference line. This is simply a horizontal like segment which provides the basis for all other parts of the symbol. It must appear on the drawing as a horizontal line, because there is significance whether information lies above or below the line.
The next element of the welding symbol is the arrow. This line segment is connected to one end of the reference line and points tone side of the weld joint. This is now gives significance to the terms arrow side and other side. That is the side to which the arrow points are referred to as the arrow side, while the opposite side is called the other side. Once the arrow side and other side have been assigned by the placement of the arrow, it is now possible to specify information relating to either or both sides.
The AWS convention is that any information placed below the reference line relates to the arrow side of the joint and that information above the reference line describes what will occur on the other side of the joint. This is illustrated in Figure 4.2
Fig No.4.2 arrow side and other side
This rule will never change, no matter which end of the reference line is attached to the arrow or which direction the arrow may point. Figure 4.3 shows several welding symbols depicting arrow side welds, but with the arrow oriented in different directions and at either end of the reference line. However, the operations will be performed on the side of the joint to which the arrow points.
Fig No 4.3 arrow side welds
Similarly figure 4.4 depicts various welding symbols describing other side welds.
Fig No 4.4 other side welds
Figure 4.5 contains several welding symbol applications to illustrate the difference between the arrow and other sides in actual practice.
Once the reference line and arrow are in place the next element of the welding symbol can be added. This particular configuration will be Figure 4.6 illustrates the basic weld symbols which are commonly used.
These symbols will show on the reference line which is show as a dotted line in Figure 4.6. If they occur below the reference line, they refer to the arrow side, and if they are placed above the reference line, they refer to the other side of the joint. It is also interesting to note that some of the weld symbols are placed such that the reference line splits them in half (e.g spot, projection and seam welds). This simply implies that the weld has no side is called the arrow side. With the exception of the surfacing weld, which always appears as a arrow side weld, all other types can be show as arrow side, other side or both sides.
Fig No.4.6 basic weld symbols.
Most of the weld symbols appear much like the actual weld configuration, which makes it easier to remember exactly what type of weld is specified by a particular job.
Another feature which should be noted for all of those weld symbols which present welds having only one of the two members prepared is that the perpendicular side of the symbol will always appeared on the left side (eg., bevel, J and flare bevel grooves, fillet and corner flange welds). For these groove welds, the designer can designer can designate which of the two members actually receives the preparation by using an arrow with a break in the line. The convention is that the last segment of the arrow points to that member receiving the specified preparation. This is shown in Figure 4.7.
Also shown in Figures 4.7 (a), (b), (c) and (d) is the designation for reinforcing fillet welds to the completed groove welds in T and corner joints. The reinforcing fillet weld symbol is attached to the extended perpendicular line which makes up one side of the groove weld symbol.
Fig 4.7 Significance of Break in Arrow Line
Groove weld detailing
After designating the type of groove weld required and at which side or sides of the joint it will be deposited, other information is necessary. Most of this data relates to dimension all requirements. Features needing dimensions include the joint configuration, weld size and the extent of welding. Let’s first discuss how various groove weld configurations are detailed on the welding symbol.
Some of the groove weld dimensions are placed with in or slightly outside the weld symbol. Referring to Figure 4.8, the 1/9” dimensions relate to the required root opening which the 60 DEG notations applies to the groove angle. Another feature illustrated here is that even though both sides of the joint receive the same treatment, it is still necessary to include how the root opening is dimensioned, and Figure 4.10 depicts other examples of groove angle details.
Fig No.; 4,8 Detailing Root opening and groove angle.
Fig 4.9 Designation of Root Opening of Groove Welds
Fig. 4.10 Designation of Groove Angle of Groove welds
Another important piece of information necessary for the individual responsible for the preparation of the groove is the depth of preparation. This dimension is shown to the left of the groove weld symbol. In Figure 4.11 the specified depth of preparation in each case is that dimension outside of the parentheses.
Fig. No. 4.11 Designation of Effective throat of groove welds with specified depth of preparation.
The dimensions show in Figure 4.11 which is enclosed in parentheses refers to the joint penetration, or effective throat required by the symbol. So far figure 4.11 (b), the joint is to be preparation weld. In the case of Figure 4.11 (c), the 3/16” depth of penetration and ½” effective throats of the welds made from either side result in a complete penetration weld.
For groove welds, if no dimensions for depth of preparation or effective throat are specified, the required weld is considered to be a complete penetration weld, as shown in Figure 4.12.
Fig No. 4.12 Full penetration weld required with no specified effective throat or depth of preparation.
Figure 4.13, is an example of the use of all of these dimensions on a groove welding symbol along with the final configuration of the required weld.
Fig No. 4.13, Groove weld symbol using combined dimensions
Fig 4.14 Application of Flare Bevel and Flare V Groove Weld Symbol
The final piece of dimensional information necessary for a groove weld is the required length. This detail is shown on the welding symbol to the right of the weld symbol. If no dimension is shown, it is assumed that the specified weld is to run the entire length of the joint. If a dimension is present to the right of the weld symbol, it refers to the length of groove weld segment required.
Flare groove welds are dimensioned as shown if figure 4.14. The depth of preparation, ‘S’ is generally considered to the radius of the member being joined or the radius of the outside radius of the member being joined or the radius of the outside surface of a bend. In each case, the effective throat is shown as ‘E’
Fillet weld detailing
There is also dimensional information pertinent to some of the weld configurations other than grooves. One of those is the fillet weld. As was the case of groove welds, the size of a fillet weld is dimensioned to the left of the weld symbol. Figure 4.15 shows numerous fillet welds and how their sizes are shown on the accompanying symbols.
Another feature identical to the groove weld application is that the length of a fillet weld is dimensioned to the right of the weld symbol. No dimension indicates that the fillet weld is to be continuous for the entire length of the joint. An example of this is shown in Figure 4.15 (f).
A common welding practice is to use intermittent fillet welds instead of a continuous fillet weld to reduce distortion and the amount of time required for welding. The dimensions for intermittent fillet welds are shown as two numbers separated by a hyphen. The first number is the length of each individual weld segment and the second number refers to the center to center spacing of these segments. The dimensioning of the length of the individual segments of welds as well as their spacing is illustrated in Figure 4.16.
The spacing from one segment to the next is referred to as the pitch. The pitch is measured as the center to center distance of each adjacent length of fillet weld.
Intermittent fillet welds may be applied to both sides of a joint in one of two ways. If the individual segments are directly across from each other, it is referred to as chain intermittent welding and the dimensioning is as shown in Figure 4.16 (b). Staggered intermittent welding is when the segments on either side of the joint coincide with spaces between individual segments on the other side of the joint. Figure 4.16 (c) shown how this type of intermittent fillet weld is dimensioned. In both types of intermittent welds, the pitch distance refers to the center to center spacing on that side of the joint only.
Fig 4.15 Application of Dimensions to Fillet Weld Symbols
Fig 4.16 Application of Dimensions to Intermittent fillet weld symbols
Fig 4.17 Application of Dimensions to Plug Weld Symbols
Plug and Slot Weld Detailing
The symbolization of the next types of welds involves several different features because of the uniqueness of their configurations. They are the plug and slot welds. As learned in Module 3 of this text, the both are welds joining overlapping members by filling a hole in the top member of connect it to the backing member. The symbol for both is simply a rectangular shape. Figure 4.17 shows some of the dimensions which can be applied to plug welds.
Figure 4.17 (a) is an example showing how the diameter of the hole of the plug weld is dimensioned. If that hole is to be of a certain size and also have sloped sides, that condition would be shown as in Figure 4.17 (b). Unless noted as in Figure 4.17 (c) a plug is assumed to be required to be filled flush with the surface of the member. Figure 4.17 (d) shown how the spacing or pitch distance of a series of plug welds is symbolized.
Finally, Figure 4.17 (e) depicts how all of these dimensions can be combined in one welding symbol.
In general, the same conventions apply to the welding symbols for slot welds, An exception however, is that the length, width, spacing, included angle of counter sink, orientation and location of slot welds cannot be shown on the welding symbol. This information shall be shown on the drawing or by a detail referenced on the welding symbol.
Spot and Seam Weld
Spot and seam welds can also be effectively described using welding symbols. Figure 4.18 shows how the size of an arc spot weld is depicted on a symbol.
Fig No. 4.18, Dimensioning of Arc Spot weld symbol
Another way in which the degree of welding can be described is by specifying the required shear strength of the resulting spot weld as is shown figure 4.19.
Fig No 4.19 Specification of spot weld strength
The pitch distance of adjacent spot welds is shown in the same manner as for plug and slot welds which can be seen in Figure 4.20.
Fig No 4.20 Dimensioning of spot weld pitch
Another feature to note in Figure 4.20 is that the spot weld symbol for this resistance weld is centered on the reference line to show that there is no side significance. If a specific number of spot welds are required in a certain area, that number can be shown as in Figure 4.21.
Fig No 21 Number of spot welds required.
Figure 4.22 Shows the combined use of several dimensions on a single symbol
Figure 4.22 Combination of spot weld dimensions.
As might be expected, the dimensioning of seam welds is similar to that of spot welds. Figure 4.23 shows the dimensioning of the size, length and pitch of intermittent seam welds, the strength of seam welds, and the extent of seam welding.
Fig 4.23 Application of dimensions to seam weld symbols
Back to Backing Weld Detailing
Two other types of welds requiring attention are the back and backing welds. While both are represented by the same weld symbol, they differ in that the back weld is deposited after one side has been welded and the backing weld is deposited before depositing the opposite side. We see in Figure 4.24 that one way to show this sequencing is through the use of a note. We will see later that multiple reference lines can be used to show a sequence of operation, so this is another way to detail which weld is deposited first. So if the back / backing weld symbol is present without some further explanation, it will be difficult to determine which type of weld is required.
Fig No 4.24 Back and Backing Weld symbols
Surfacing weld detailing
Figure 4.25 shows the various ways in which surfacing welds can be described on a welding symbol. The primary piece of information required is the thickness of this surfacing. As seen in figures 4.25 (b) and (c) the area of the surfacing cannot be shown on the symbol, but must be detailed some how on the drawing. When the symbol appears as in Figure 4.25 (c), it means that the entire surface to which the arrow points is to be covered with surfacing.
Flange Weld Detailing
The final weld symbols to be discussed are those for the various types of flange welds. Their dimensioning shows not only the size of the weld but also details as to how the flange is to be formed. Figure 4.26 shows both arrow side and other side edge flange welds are shown in Figure 4.27.
Figure 4.28 illustrates how these welds are dimensioned. The ‘C’ dimension refe3rs to the inside radius of the flange bend, while dimension ‘B’ describes the length of that flange. The final dimension ‘A’ specifies the effective throat of the required weld.
Fig 4.25 Application of Surfacing weld symbol
Fig 4.26 Application of Edge Flange weld symbol
Fig 4.27 Application of corner flange weld symbol
Fig 4.28 Application of Edge and Corner Flange weld symbol
Although we have discussed the basic weld symbols land how they are dimensioned, there are still additional symbols which can be employed to detail other important information. This group of symbols to as supplementary symbols, because they can be combined with many of the weld symbols already discussed. These supplementary are shown in Figure 4.29.
Fig No 4.49 supplementary symbols
The first of these symbols to be talked about here is the weld all around symbol. This symbol, consisting of a circle around the junction of the arrow and reference line, describes a weld which is to be continuous around some joint. Even though there may be abrupt changes in direction. Figure 4.30 and 4.31 give examples of how the weld all-around symbol is to be utilized.
Another commonly used supplementary symbol is the field weld symbol. This symbol, shown as a flag at the junction of the arrow and reference line, details those welds requiring welding in the field rather than being done in the shop. As a matter of convention. The symbol will always appear above the reference line, regardless of on which side the welding will be performed. Also, as shown in Figure 4.32 the flan will always point away from the arrow.
Fig No 4.32 Field Weld Symbol
The next supplementary symbol commonly utilized is the melt thru symbol. As shown in Figure 4.33 it can be applied to numerous types of weld symbols to describe weld penetration beyond the back surface of the joint. The melt thru symbol itself appears as a darkened in back / backing weld symbol. The amount of melt thru can be detailed by including a dimension to the left of the symbol
Another way to show the backside treatment of a weld is through the use of symbol for backing or spacer material, if a weld requires some type of backing material or a spacer with in the joint, it can be symbolized as shown in Figure 4.34
Fig 4.30 Application of weld All Around Symbol
Fig 4.31 Application of weld All Around Symbol
Fig 4.33 Application of Melt-Thru Symbol
Fig 4.34 Joints with Backing
Fig 4.35 Joints with Spacers
Fig 4.36 Application of Flush and convex symbols to groove weld symbol
While this symbol appears similar to the plug weld symbol, it differs in that there are the letter ‘M’ or ‘MR’ within the symbol. The ‘M’ refers to the type of material to be used for backing. It could be the same metal as the base material copper ceramic flux etc. what ever type of material is desired there must be some note to that effect on the drawing. If the ‘MR’ notation appears, it means that whatever backing has been specified must be removed following welding.
The use of spacers and their accompanying symbols is shown in figure 4.35. As shown here, these spacers can be applied to various types of weld configurations, like the backing material symbol, specific details of the spacer must be given else where on the drawing.
The last group of supplementary symbols to be discussed are those which describe the desired shape of the completed weld. There are contour symbols for various configurations, including, flush, convex and concave. The symbols for these contours correspond to the actual configurations desired. Figure 4.36 shows some examples of how these contour symbols are utilized
The Tail of the Symbol
The final element of the welding symbol is referred to as the tail. While not considered to be an essential element of a welding symbol, it can be used effectively to convey other important information which cannot be conveniently communicated elsewhere on the welding symbol, when utilized, the tail is placed on the end of the reference line opposite the arrow. Some of the typical information which cold be included in the tail are, procedure number, process type, specification number, filler metal type, need for back gouging, reference to other drawing details etc. Figure 4.37 shows how the tail is used reference particular specifications.
Fig No 4.37, Specification References in Tail of Welding Symbol
In figure 4.38, the tail contains information relating to the type of welding process to be used, where the process is identified by its proper letter designation
Fig No 4.38 Process reference in Tail of welding symbol
The complete listing of the letter designations for all of the welding and allied processes in shown in Figure 4.39
Figure 4.40 illustrates how the tail can be used to specify complete penetration weld requirement where the actual joint preparation is optional. That is, the weld is required to be a complete penetration weld, but the designer has left the choice of weld preparation to the fabricator.
Fig No 4.40 complete penetration required joint preparation optional
Use of Multiple Reference Lines
All of the discussion thus far has dealt with the use of various weld symbols along with other elements to create a welding symbol capable of describing the requirements for welding some particular weld joint. It some times becomes important to convey more detailed explanations of exactly how a weld is to be performed. For one thing, it is often convenient to describe the order, or sequence, of the entire welding operation. This becomes more important when the weld joint in question requires measures to prevent excessive distortion or reduce the possibility of cracking due to high restraint.
One way to describe this sequence of operations is to combine several individual reference lines on the same arrow. Each reference line could contain information to be applied at a certain step in the welding operation. The convention is that the order of these operations depends on the relative location of each reference line with respect to the arrow. That is the first operation is described by the reference line closest to the arrow. Reference lines for subsequent operations will then appear in order moving away from the arrow such that the last operation is described by that reference line furthest from the arrow. Examples of welding symbols utilizing multiple reference lines are illustrated in Figure 4.41
Fig No. 4.41 Sequence of operations shown by multiple reference lines
The use of multiple reference lines is often convenient to show the need for back gouging, as shown in Figure 4.42
Fig No 4.42 Use of multiple reference lines to show need for back gouging.
Figure 4.43 shows some what of a summary of many of these types of welding symbols by depicting their use on a structural drawing.
Fig 4.43 Use of Welding Symbols on structural drawing
The use of welding symbols can also be applied to various brazing joints as well, with some minor changes, Figure 4.44 illustrates how some brazing symbols are applied.
Since there are so many different types of brazing (see subject 9), it is necessary to specify which process is to be used by placing its letter designation in the tail of the symbol.
When a brazing symbol is utilized, there are certain dimensions which should be specified to fully describe the important aspects of the braze joint. Figure 4.45 shows examples of brazing symbols for lap joints.
The ‘C1’ dimension within the square-groove symbol describes the amount of clearance between the two members when fit up. The ‘L; dimension refers to the amount of overlap and the ‘S’ details the size of the reinforcing fillet on the outside of the joint. While the symbols for some of the braze joints are identification those used for welding, the scarf groove is a joint design specifically for use with brazing. Figure 4.46 is an example of the application of a brazing symbol to a scarf groove.
Fig 4.44 Application of Brazing Symbols
Fig 4.45 Application of Braze symbols on lap joints
Fig No 4.46 Braze symbols on scarf joint
Fig 4.47 Application of Brazing Symbols