Groove Welds

The groove weld is commonly used to make edge-to-edge joints, although it is also often used in corner joints, T joints, and joints between curved and flat pieces. As suggested by the variety of groove weld symbols, there are many ways to make a groove weld, the differences depending primarily on the geometry of the parts to be joined and the preparation of their edges. Weld metal is deposited within the groove and penetrates and fuses with the base metal to form the joint. (Note: for the sake of graphical clarity, the drawings below generally do not show the penetration of the weld metal. Recognize, however, that the degree of penetration is important in determining the quality of the weld.)

The various types of groove weld are:

The square groove weld, in which the "groove" is created by either a tight fit or a slight separation of the edges. The amount of separation, if any, is given on the weld symbol.

The V-groove weld, in which the edges of both pieces are chamfered, either singly or doubly, to create the groove. The angle of the V is given on the weld symbol, as is the separation at the root (if any).

If the depth of the V is not the full thickness--or half the thickness in the case of a double V--the depth is given to the left of the weld symbol.

If the penetration of the weld is to be greater than the depth of the groove, the depth of the effective throat is given in parentheses after the depth of the V.

The bevel groove weld, in which the edge of one of the pieces is chamfered and the other is left square. The bevel symbol's perpendicular line is always drawn on the left side, regardless of the orientation of the weld itself. The arrow points toward the piece that is to be chamfered. This extra significance is emphasized by a break in the arrow line. (The break is not necessary if the designer has no preference as to which piece gets the edge treatment or if the piece to receive the

treatment should be obvious to a qualified welder.) Angle and depth of edge treatment, effective throat, and separation at the root are described using the methods discussed in the V-groove section.

The U-groove weld, in which the edges of both pieces are given a concave treatment. Depth of edge treatment, effective throat, and separation at the root are described using the methods discussed in the V-groove section.

The J-groove weld, in which the edge of one of the pieces is given a concave treatment and the other is left square. It is to the U-groove weld what the bevel groove weld is to the V-groove weld. As with the bevel, the perpendicular line is always drawn on the left side and the arrow (with a break, if necessary) points to the piece that receives the edge treatment. Depth of edge treatment, effective throat, and separation at the root are described using the methods discussed in the V-groove section.

The flare-V groove weld, commonly used to join two round or curved parts. The intended depth of the weld itself are given to the left of the symbol, with the weld depth shown in parentheses.

The flare bevel groove weld, commonly used to join a round or curved piece to a flat piece. As with the flare-V, the depth of the groove formed by the two curved surfaces and the intended depth of the weld itself are given to the left of the symbol, with the weld depth shown in parentheses. The symbol's perpendicular line is always drawn on the left side, regardless of the orientation of the weld itself.

Common supplementary symbols used with groove welds are the melt-thru and backing bar symbols. Both symbols indicate that complete joint penetration is to be made with a single-sided groove weld. In the case of melt-thru, the root is to be reinforced with weld metal on the back side of the joint. The height of the reinforcement, if critical, is indicated to the left of the melt-thru symbol, which is placed across the reference line from the basic weld symbol.

When a backing bar is used to achieve complete joint penetration, its symbol is placed across the reference line from the basic weld symbol. If the bar is to be removed after the weld is complete, an "R" is placed within the backing bar symbol. The backing bar symbol has the same shape as the plug or slot weld symbol, but context should always make the symbol's intention clear.

Fillet Welds

The fillet weld (pronounced "FILL-it," not "fil-LAY") is used to make lap joints, corner joints, and T joints. As its symbol suggests, the fillet weld is roughly triangular in cross-section, although its shape is not always a right triangle or an isosceles triangle. Weld metal is deposited in a corner formed by the fit-up of the two members and penetrates and fuses with the base metal to form the joint. (Note: for the sake of graphical clarity, the drawings below do not show the penetration of the weld metal. Recognize, however, that the degree of penetration is important in determining the quality of the weld.)

The perpendicular leg of the triangle is always drawn on the left side of the symbol, regardless of the orientation of the weld itself. The leg size is written to the left of the weld symbol. If the two legs of the weld are to be the same size, only one dimension is given; if the weld is to have unequal legs (much less common than the equal-legged weld), both dimensions are given and there is an indication on the drawing as to which leg is longer.

The length of the weld is given to the right of the symbol.

If no length is given, then the weld is to be placed between specified dimension lines (if given) or between those points where an abrupt change in the weld direction would occur (like at the end of the plates in the example above).

For intermittent welds, the length of each portion of the weld and the spacing of the welds are separated by a dash (length first, spacing second) and placed to the right of the fillet weld symbol.

Notice that the spacing, or pitch, is not the clear space between the welds, but the center-to-center (or end-to-end) distance.

For more information, see ANSI/AWS A2.4, Symbols for Welding and Nondestructive Testing.

Plug and Slot Welds

Plug welds and slot welds are used join overlapping members, one of which has holes (round for plug welds, elongated for slot welds) in it. Weld metal is deposited in the holes and penetrates and fuses with the base metal of the two members to form the joint. (Note: for the sake of graphical clarity, the drawings below do not show the penetration of the weld metal. Recognize, however, that the degree of penetration is important in determining the quality of the weld.)

For plug welds, the diameter of each plug is given to the left of the symbol and the plug-to-plug spacing (pitch) is given to the right. For slot welds, the width of each slot is given to the left of the symbol, the length and pitch (separated by a dash) are given to the right of the symbol, and a detail drawing is referenced in the tail. The number of plugs or slots is given in parentheses above or below the weld symbol. The arrow-side and other-side designations indicate which piece contains the hole(s). If the hole is not to be completely filled with weld metal, the depth to which it is to be filled is given within the weld symbol.

The structure of the welding symbol

The horizontal line--called the reference line--is the anchor to which all the other welding symbols are tied. The instructions for making the weld are strung along the reference line. An arrow connects the reference line to the joint that is to be welded. In the example above, the arrow is shown growing out of the right end of the reference line and heading down and to the right, but many other combinations are allowed.

Quite often, there are two sides to the joint to which the arrow points, and therefore two potential places for a weld. For example, when two steel plates are joined together into a T shape, welding may be done on either side of the stem of the T.

The weld symbol distinguishes between the two sides of a joint by using the arrow and the spaces above and below the reference line. The side of the joint to which the arrow points is known (rather prosaically) as the arrow side, and its weld is made according to the instructions given below the reference line. The other side of the joint is known (even more prosaically) as the other side, and its weld is made according to the instructions given above the reference line. The below=arrow and above=other rules apply regardless of the arrow's direction.

The flag growing out of the junction of the reference line and the arrow is present if the weld is to be made in the field during erection of the structure. A weld symbol without a flag indicates that the weld is to be made in the shop. In older drawings, a field weld may be denoted by a filled black circle at the junction between the arrow and the reference line.

The open circle at the arrow/reference line junction is present if the weld is to go all around the joint, as in the example below.

The tail of the weld symbol is the place for supplementary information on the weld. It may contain a reference to the welding process, the electrode, a detail drawing, any information that aids in the making of the weld that does not have its own special place on the symbol.

Types of welds and their symbols

Each type of weld has its own basic symbol, which is typically placed near the center of the reference line (and above or below it, depending on which side of the joint it's on). The symbol is a small drawing that can usually be interpreted as a simplified cross-section of the weld. In the descriptions below, the symbol is shown in both its arrow-side and other-side positions.

Bolt tension & joint behaviorThe usual purpose of a bolted joint is to clamp two or more parts together. The clamping force is achieved by applying torque to the bolt head and the nut; the mechanical advantage of the wrench and threads allows one to actually stretch the section of the bolt between the head and the

nut (an area known as the grip), creating tension in the bolt. This tension is known as pretension because it exists before any other forces are applied to the joint.

The pretension is transmitted to the mating parts through the head, nut, and any washers that may be present. It squeezes the mating parts together, and--if the joint is designed, assembled, and maintained properly--prevents the mating parts from separating or sliding under normal loads.

The pretension in a bolt is often quite high--70% of the bolt's tensile strength is not uncommon. At first glance it may seem that this leaves very little strength left to carry the externally applied loads, but it turns out that bolted joints are pretty clever when it comes to carrying loads, and their capacity is greater than you might expect.

Consider the joint shown below, two D-shaped yokes clamped together with a single bolt. First the bolt is tightened. This draws the faying surfaces (the portions of the mating parts that come in contact) together and applies a compressive force to the mating parts. The joint is in equilibrium, with the compressive force across the faying surfaces equal in magnitude to the pretension in the bolt.

As the external tensile load is applied to the joint, the joint responds by distributing the load. As expected, part of the load goes into the bolt, increasing its tension. But part of the load also goes into the mating parts, decreasing the compression at the faying surfaces. In most joints, this decrease in compression absorbs most of the applied load, shielding the bolt from large increases in tension. Exactly how much is shielded depends on the geometry and material makeup of the joint, but it is not unusual for as much as 90% of the applied load to be taken by the faying surfaces, leaving only 10% to be borne by the bolt.

Of course, the compression at the faying surfaces can only decrease so far. Once the compression has been reduced to zero, the faying surfaces lose contact with each other and the bolt then carries all the applied load. A graph of the bolt tension vs. the applied load shows this change in behavior as a kink at the point at which the faying surfaces part (sometimes referred to as the decompression point.

Parting of the faying surfaces is generally considered a bad thing, especially in joints that are subjected to fluctuating loads. If the applied load cycles back and forth between levels below the decompression point, the cyclic stress range in the bolt is relatively low. If, however, the applied load cycles to levels beyond the decompression point, the cyclic stress range in the bolt jumps dramatically and can lead to an early fatigue failure. The graph below shows how a lowered pretension can create this effect.

For this reason, fatigue failures in bolts are often associated with low pretension.

Hex Head Bolt MarkingsThe strength and type of steel used in a bolt is supposed to be indicated by a raised mark on the head of the bolt. The type of mark depends on the standard to which the bolt was manufactured. Most often, bolts used in machinery are made to SAE standard J429, and bolts used in structures are made to various ASTM standards. The tables below give the head markings and some of the most commonly-needed information concerning the bolts. For further information, see the appropriate standard.

SAE Bolt Designations

SAEGradeNo.

Sizerange

Tensilestrength,

ksi Material Head marking

1

2

1/4 thru 1-1/2

1/4 thru 3/47/8 thru 1-1/2

60

7460

Low or mediumcarbon steel

5 1/4 thru 11-1/8 thru 1-1/2

120105

Medium carbon steel,quenched & tempered

5.2 1/4 thru 1 120 Low carbonmartensite steel,

quenched & tempered

7 1/4 thru 1-1/2 133 Medium carbonalloy steel,

quenched & tempered

8 1/4 thru 1-1/2 150 Medium carbonalloy steel,

quenched & tempered

8.2 1/4 thru 1 150 Low carbonmartensite steel,

quenched & tempered

ASTM Bolt Designations

ASTMstandard

Sizerange

Tensilestrength,

ksi Material Head marking

A307 1/4 thru 4 60 Low carbon steel

A325Type 1

1/2 thru 11-1/8 thru 1-1/2

120105

Medium carbon steel,quenched & tempered

A325Type 2

1/2 thru 11-1/8 thru 1-1/2

120105

Low carbonmartensite steel,

quenched & tempered

A325Type 3

1/2 thru 11-1/8 thru 1-1/2

120105

Weathering steel,quenched & tempered

A449 1/4 thru 11-1/8 thru 1-1/2

1-3/4 thru 3

12010590

Medium carbon steel,quenched & tempered

A490Type 1

1/4 thru 1-1/2 150 Alloy steel,quenched & tempered

A490Type 3

1/4 thru 1-1/2 150 Weathering steel,quenched & tempered

Often one will find "extra" marks on a bolt head--marks in addition to those shown above. Usually these marks indicate the bolt's manufacturer.

ASTM A325 Type 2 bolts have been discontinued, but are included above because they can be found in existing structures. Their properties can be important in failure investigations.

While the bolts shown above are among the most common in the U.S., the list is far from exhaustive. In addition to the other bolts covered by the SAE and ASTM standards, there are a host of international standards, of which ISO is perhaps the most well known.

WELDING SYMBOLS

Special symbols are used on a drawing to specify where welds are to be located, the type of joint to be used, as well as the size and amount of weld metal to be deposited in the joint. These symbols have been standardized by the American Welding Society (AWS). You will come into contact with these symbols anytime you do a welding job from a set of blueprints. You need to have a working knowledge of the basic weld symbols and the standard location of all the elements of a welding symbol.

A standard welding symbol (fig. 3-43) consists of a reference line, an arrow, and a tail. The reference line becomes the foundation of the welding symbol. It is used to apply weld symbols, dimensions, and other data to the weld. The arrow simply connects 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. The tail of the welding symbol is used only when necessary to include a specification, process, or other reference information.

Weld Symbols

The term weld symbol refers to the symbol for a specific type of weld. As discussed earlier, fillet, groove, surfacing, plug, and slot are all types of welds. Basic weld symbols are shown in figure 3-44. The weld

Figure 3-44.-Basic weld symbols.

Figure 3-45.-Weld symbols applied to reference line.

Figure 3-46.-Specifying weld locations.

Figure 3-47.-Arrowhead indicates beveled plate.

symbol is only part of the information required in the welding symbol. The term welding symbol refers to the total symbol, which includes all information needed to specify the weld(s) required.

Figure 3-45 shows how a weld symbol is applied to the reference line. Notice that the vertical leg of the weld symbol is shown drawn to the left of the slanted leg. Regardless of whether the symbol is for a fillet, bevel, J-groove, or flare-bevel weld, the vertical leg is always drawn to the left.

Figure 3-46 shows the significance of the positions of the weld symbols position on the reference line. In view A the weld symbol is on the lower side of the reference line that is termed the arrow side. View B shows a weld symbol on the upper side of the reference line that is termed the other side. When weld symbols are placed on both sides of the reference line, welds must be made on both sides of the joint (view C).

When only one edge of a joint is to be beveled, it is necessary to show which member is to be beveled. When such a joint is specified, the arrow of the welding symbol points with a definite break toward the member to be beveled. This is shown in figure 3-47.

Figure 3-48 shows other elements that may be added to a welding symbol. The information applied to the reference line on a welding symbol is read from left to right regardless of the direction of the arrow.

Dimensioning

In figure 3-48, notice there are designated locations for the size, length, pitch (center-to-center spacing), groove angle, and root opening of a weld. These locations are determined by the side of the reference line on which the weld symbol is placed. Figure 3-49 shows how dimensions are applied to symbols.

Figure 3-48.-Elements of a welding symbol.

Figure 3-49.-Dimensions applied to weld symbols.

Figure 3-50.-Dimensioning of welds.

Figure 3-51.-Supplementary symbols.

Figure 3-50 shows the meaning of various welding dimension symbols. Notice that the size of a weld is shown on the left side of the weld symbol (fig. 3-50, view A). The length and pitch of a fillet weld are indicated on the right side of the weld symbol. View B shows a tee joint with 2-inch intermittent fillet welds that are 5 inches apart, on center. The size of a groove weld is shown in view C. Both sides are 1/2 inch, but note that the 60-degree groove is on the other side of the joint and the 45-degree groove is on the arrow side.

Supplementary Symbols

In addition to basic weld symbols, a set of supplementary symbols may be added to a welding symbol. Some of the most common supplementary symbols are shown in figure 3-51.

Contour symbols are used with weld symbols to show how the face of the weld is to be formed. In addition to contour symbols, finish symbols are used to indicate the method to use for forming the contour of the weld.

When a finish symbol is used, it shows the method of finish, not the degree of finish; for example, a C is used to indicate finish by chipping, an M means machining, and a G indicates grinding. Figure 3-52 shows how contour and finish symbols are applied to a weldng symbol. This figure shows that the weld is to be ground flush. Also, notice that the symbols are placed on the same side of the reference line as the weld symbol.

Figure 3-52.-Finish and contour symbols.

Figure 3-53.-Specifying additional welding information.

Another supplementary symbol shown in figure 3-51 is the weld-all-around symbol. When this symbol is placed on a welding symbol, welds are to continue all around the joint.

Welds that cannot be made in the shop are identified as field welds. Afield weld symbol is shown in figure 3-51. This symbol is a black flag that points toward the tail of the welding symbol.

Specifying Additional Information

It is sometimes necessary to specify a certain welding process, a type of electrode, or some type of reference necessary to complete a weld. In this case, a note can be placed in the tail of the reference line. (See

Figure 3-55.-Example of welding symbol in use.

fig. 3-53.) If additional information is not needed, then the tail is omitted.

Multiple-Weld Symbols

When you are fabricating a metal part, there are times when more than one type of weld is needed on the same joint; for example, a joint may require both a bevel groove weld and a fillet

weld. Two methods of illustrating these weld symbols are shown in figure 3-54. Note that in each welding symbol, the bevel groove weld is to be completed first, followed by the fillet weld.

Applying a Welding Symbol

Figure 3-55 shows an example of how a welding symbol may appear on a drawing. This figure shows a

steel pipe column that is to be welded to a baseplate. The symbol tells the welder that the pipe is to be beveled at a 30-degree angle followed by a bevel groove weld all around the joint. This is followed by a 1/2-inch fillet weld that is also welded all around the joint. Finally, finish the fillet weld by grinding it to a flush contour. As the field weld symbol indicates, all welds are to be accomplished in the field.

For additional information about welding symbols, refer to

The British Standard for weld symbols is BS EN 22553. When identification of the weld process is required as part of the weld symbol the relevant weld process code is listed in BS EN ISO 4063.

Basic Weld Symbol

The weld symbol always includes

1. An arrow line 2. A reference line 3. A symbol

Note: Weld symbols on the full reference line relates to welds on the near side of the plate being welded. Weld symbols on the dashed line relates to weld on the far side of the plate. If the

welds are symmetrical on both sides of the plate the dashed line is omitted. If the dashed line is above the full line then the symbol for the nearside weld is drawn below the reference line and the symbol for the farside weld is above the dashed line

More Detailed Symbolic Representation of Weld

Welding.....Weld process numbers.

Table of Weld Symbols

Complementary Symbols

Supplementary Indication

Dimensioning Welds

A review of the application of weld symbols on drawings - Part 1

Weld symbols have been used for many years and are a simple way of communicating design office details to a number of different industrial shop floor personnel such as welders, supervisors, and inspectors. Subcontractors are often required to interpret weld symbols on engineering drawings, from perhaps the main contractor or client. It is essential that everyone should have a full understanding of weld symbol requirements to ensure that the initial design requirement is met.

There are a number of standards which relate to weld symbols including British, European, International and American (American Welding Society) standards. Most of the details are often similar or indeed, the same, but it is essential that everyone concerned knows the standard to be used. One of the first requirements therefore is:

Which standard?The UK has traditionally used BS 499 Part 2. This standard has now been superseded by BS EN 22553, however in many welding and fabrication organisations there will be old drawings used that make reference to out of date standards such as BS 499 Pt 2.

BS EN 22553 is almost identical to the original ISO 2553 standard on which it was based. Therefore we can say, for at least this article's scope, there are no significant differences, but it is essential that the reader consults the specific standard. The American system is also similar in many respects but will not be covered here.

Basic requirementsAll the standards have the same requirements in relation to the following items:

• Arrow line and arrow head • Reference line

The arrow line can be at any angle (except 180 degrees) and can point up or down. The arrow head must touch the surfaces of the components to be joined and the location of the weld. Any intended edge preparation or weldment is not shown as an actual cross sectional representation, but is replaced by a line. The arrow also points to the component to be prepared with single prepared components. See Figs. 1-4.

Fig. 1. Fig. 2.

Fig. 3. Fig. 4.

Symbol typesTo the basic set-up of the arrow and reference line, the design draughtsperson can apply the appropriate symbol, or symbols for more complex situations.

The symbols, in particular for arc and gas welding, are often shown as cross sectional representations of either a joint design or a completed weld. Simple, single edge preparations are shown in Fig. 5.

For resistance welding, a spot weld and seam weld are shown in Fig. 6:

Fig. 5. Fig. 6.

Joint and/or weld shapeThe above examples can be interpreted as either the joint details alone or the completed weld, however, for a finished weld it is normal to find that an appropriate

weld shape is specified. Using the examples above, there are a number of options and methods to specify an appropriate weld shape or finish.

Butt welded configurations would normally be shown as a convex profile (Fig.7 'a', 'd' and 'f') or as a dressed-off weld as shown in 'b' and 'c'. Fillet weld symbols are always shown as a 'mitre' fillet weld (a right angled triangle) and a convex or concave profile can be superimposed over the original symbol's mitre shape. See Fig. 7.

Fig. 7.

Part 2 of this explanation of weld symbols covering more complex situations will appear in the next issue.

Weld sizing

In order that the correct size of weld can be applied, it is common to find numbers to either the left or to the right of the symbol.

For fillet welds, numbers to the left of the symbol indicate the design throat thickness, leg length, or both design throat thickness and leg length requirements. Figure 1 gives examples of symbols used in different Standards.

Fig.

For fillet welds:

Superseded BS499 Pt 2 gives

a = design throat thickness b = leg length

ISO 2553/EN 22553 requirements

a = design throat thickness z = leg length s = penetration throat thickness

For butt joints and welds, an S with a number to the left of a symbol refers to the depth of penetration as shown in Fig.2.

Fig.

When there are no specific dimensional requirements specified for butt welds on a drawing using weld symbols, it would normally be assumed that the requirement is for a full penetration butt weld ( Fig.3).

Fig.

Numbers to the right of a symbol or symbols relate to the longitudinal dimension of welds, eg for fillets, the number of welds, weld length and weld spacing for non-continuous welds, as Fig.4.

Fig.

On fillet welded joints made from both sides, a staggered weld can be shown by placing a 'Z' through the reference line ( Fig.5).

Fig.

Supplemetary symbols

Weld symbols indicate the type of preparation to use or the weld type. However, there may still be occasions where other information is required. The basic information can therefore be added to in order to provide further details as shown in Figs.6, 7 and 8.

Fig.

Fig.7 Fig.8

Weld all round

For a Rectangular Hollow Section (RHS) welded to a plate, for example:

Weld in the field or on site

The box attached to the arrow can be used to contain, or point to, other information.

Welding process type

ISO 4063 gives welding processes specific reference numbers. As shown in Fig.9 the appropriate process number is placed in the tail of the arrow. Other processes are given a unique number. In this example, 135 refers to MAG welding.

Fig.

There are a number of additional symbols given in the Standards ( eg ISO 22553) which refer to additional welding or joint requirements. Figure 10 shows the requirement for a sealing run.

Fig.1

Compound joints/welds

A compound weld could be a 'T' butt weld which requires fillet welds to be added to increase the throat thickness as shown in Fig.11.

Fig.1

The broken reference line

The main feature that distinguishes weld symbol standards is that for ISO 2553 and BS EN 22553, there is an additional feature of a broken reference line.

This method is used when a weldment or weld preparation needs to be specified on the 'other side' of the arrow as shown in Fig.12.

Any symbol that is used to show a joint or weld type feature on the other side of the arrow line is always placed on a dotted line.

BS 499 and AWS require symbols to be placed above the reference line (which indicate the other side) or below the reference line (indicating the arrow side).

Summary

Weld symbols are a very useful way of communicating welding requirements from the design office to the shop floor.

It is essential that the 'rules' of the standard used are correctly applied by drawing office personnel. However, it is also important that shop floor personnel are able to read and understand the details of weld symbols.

Much of this requirement can be met by reference to the standard being used within the organisation and by the drawing office personnel considering the needs of the end user such as the welders, welding supervisors, welding inspection personnel and welding engineers in order to minimise costly mistakes due to misinterpretation.

Training of all personnel in the correct use of weld symbol specifications also plays an important role in ensuring that weld symbols are both correctly applied and correctly read.

Welding Symbols: A Useful System or Undecipherable Hieroglyphics?

Bill Green Former National Board ConsultantRetired Professor Emeritus in Welding Engineering, The Ohio State University

Winter 1996

Category: Design/Fabrication

Fig.12

Summary: The following article is a part of National Board Classic Series and it was published in the National Board BULLETIN . (6 printed pages)

Welding symbols, when properly applied to drawings and, as importantly, when correctly interpreted, offer a potentially convenient way of controlling the welding of a particular joint.

The need for consistency in both the application of welding symbols to engineering drawings, and the accurate interpretation by personnel directly involved in manufacturing or construction, led to the development of a standard for these activities. The current American standard for welding symbols was originated by the American Welding Society and approved by the American National Standards Institute as ANSI/AWS A2.4-93, Standard Symbols for Welding, Brazing and Nondestructive Examination.

Part A of this standard covers welding symbols, Part B deals with brazing symbols, and Part C describes symbols for specifying nondestructive examinations.

Welding SymbolsAlthough the basic symbol system is uniform, there is a need for some flexibility, as specific circumstances differ from one shop to another and field operations may involve entirely different situations. There are, therefore, often several ways to specify a given weld. Also, because cost is a consideration and is related to the specific equipment to be used, the details of joint geometry will vary from one manufacturer to another.

There is a considerable advantage to developing a shop standard for use with welding symbols. A shop standard for this purpose will establish the details that apply to all normal or standard joints. Welding symbols can therefore specify the welding without including all of the many possible details within the symbols. Simpler welding symbols are easier to add to a drawing and to interpret. Fewer errors are a benefit of this approach.

This article focuses on those welding symbols associated with typical applications with ASME Code items.

The ArrowThe first element of a welding symbol to consider is the arrow. The arrow is an essential part of every welding symbol and must point to the joint to be welded. The stem of the arrow should not be a horizontal line on the drawing. The side of the joint to which the arrow points is, by definition, the "arrow side" of the joint, and the opposite side of the joint is the "other side" of the joint (Figure 1).

Often only limited space is available on a drawing for welding symbols. To minimize the number of welding symbols required, it is permissible to use more than one arrow in a single welding symbol if each joint to which an arrow is pointing is to be welded in exactly the same way. Since a welding symbol specifies welding of only the joint to which an arrow is pointing, and a change of direction or change in geometry constitutes the end of a joint, a multiple arrow welding symbol can be very helpful, particularly around closed corners (Figure 2).

The Reference LineAnother essential part of all welding symbols is the reference line, which is a straight line, drawn horizontally on a drawing, and connected to the arrow. The arrow may be connected to either end of the reference line (Figure 1).

Information relating to the "arrow side" of the joint is placed below the reference line and information relating to the "other side" of the joint is placed above the reference line. These positional relationships exist whether the arrow is attached to the left or right end of the reference line, and do not change as the angle between the arrow and the reference line varies (Figure 1).

The sequence of operations necessary to produce a specified weld is not indicated by the normal single-reference-line welding symbol. For example, if welding is to be done on both the "arrow" and "other" sides of a joint (typically called a double weld), a single-reference-line welding symbol does not

specify which side of the joint is to be welded first. In fact, the symbol does not specify completion of the welding from one side prior to the start of the welding on the opposite side. These details are normally left to the personnel interpreting the welding symbol, with the requirements of the completed weld specified by the symbol.

If the sequence of operations needs to be specified, a multiple-reference-line welding symbol may be used. Two or more reference lines may be connected to the same arrow, with the reference line closest to the arrow specifying the first operation, followed by the operations specified by the sequence of reference lines reading upward or downward from the arrow (Figure 3). It should be noted that operations other than welding, such as nondestructive examinations, can be specified by a multiple-reference-line symbol.

The TailA third element to be considered is the "tail" of the welding symbol. The tail is drawn as agreater-than (>) or less-than(<) symbol, connected at the end of the reference line opposite the arrow. Information for which there is no specific provision elsewhere in the symbol is placed to the left or right of the tail as appropriate.

Reference to the approved welding procedure specification (WPS) is an example of information appropriate in the tail of a welding symbol. Since a WPS can contain all of the details applicable to a specific joint, a welding symbol composed of an arrow, reference line, tail and applicable WPS designation would be sufficient to completely specify the welding of the joint.

The welding process to be used is often specified by entering process designation letters in the tail of the welding symbol. The American standard includes two lists of processes and their corresponding designation letters. Table 1 groups similar processes, such as arc welding, brazing, resistance welding, and thermal cutting, while Table 2 arranges the processes alphabetically.

Groove WeldsAdditional information may be included in a welding symbol, even if also included in a WPS. For example, V-, U-, bevel-, or J-groove welds may be specified to provide increased weld size in a given joint, compared to that obtainable with a square-groove weld. The choice is usually made on the basis of cost for the completed weld. A groove-weld symbol may be added to a welding symbol, below the reference line, to specify a weld only on the "arrow side" of the joint (single weld); above the reference line, to specify a weld only on the "other side" of the joint (also a single weld); or weld symbols may be added both below and above the reference line, to specify a double weld (Figure 4).

Complete Joint PenetrationSince many applications require welds providing complete joint penetration (CJP), there are several ways to specify this condition. One way is to use an arrow, a reference line, and add CJP in the tail of the symbol. This symbol specifies complete joint penetration with no detail as to how the final condition is to be achieved. Such a symbol may be appropriate when there is uncertainty as to what specific equipment will be available when the work is to go through the shop. Later, when equipment availability is known, it is a good practice to submit assembly drawings to engineering for final approval, with welding symbols containing all pertinent details.

A second way to specify complete joint penetration is to include a single groove-weld symbol or double groove-weld symbols (must be the

same weld symbol on both sides of the reference line), without any dimensions to indicate depth of bevel or weld size. It should be noted that partial joint penetration can be specified by adding the

depth-of-bevel dimension and the required weld size (in parentheses) to the left of the groove-weld symbol or both symbols of a double weld (Figure 5).

Inclusion of a backing weld symbol or back-weld-symbol, opposite a groove-weld symbol, specifies complete joint penetration if no depth-of-bevel or weld-size dimensions are added. Also, the inclusion of a backing symbol, opposite a groove-weld symbol, again without depth-of-bevel or weld-size dimensions, specifies complete joint penetration (Figure 6). Although there are provisions for specifying the root opening (gap), groove angle, and finish contours of welds, it is suggested that these details are best specified by a shop standard.

A discussion of groove welds should include at least mention of the scarf weld, a type of weld used on lighter gage material in small diameter piping, tube-to-tubesheet applications, and attachment of seats in smaller valves. This type of weld is intended for use with brazed joints, covered in Part B of the standard. There are two additional groove-weld types: the flare-bevel and the flare-V. These welds are used extensively in industries in which solid rounds, piping, and square and rectangular tubing are employed for structural purposes, rather than withstanding internal pressures typical of boilers and pressure vessels. The flare-type groove welds are therefore more common in the construction of buildings that house ASME Code items than in the manufacture of the items.

In a few cases there may be need to specify complete joint penetration plus a measurable reinforcement on the root side of a single-welded joint (welding from one side only). The addition of the "melt-through" symbol, on the opposite side of the reference line from a groove-weld symbol, identifies this requirement. The height of the root reinforcement may be specified by adding the appropriate dimension to the left of the melt-through symbol (Figure 7).

The use of consumable inserts has become more popular over the years, particularly in pipe joints, creating the need for a symbol to specify them. An open square, placed on the reference line opposite a groove-weld symbol, indicates the requirement for a consumable insert. The AWS consumable insert class must be added to the tail of the welding symbol, unless that information is specified in some other way (Figure 7).

Fillet WeldsFillet welds are used extensively in industries including those producing boilers and pressure vessels. The fillet weld symbol is a right triangle placed on the reference line with the perpendicular leg always on the left. The dimension specifying the leg size of a fillet weld is placed to the left of the fillet weld symbol, and on the same side of the reference line.

Since the load-carrying capacity per pound of fillet weld is greatest for equal-leg fillet welds, they are used unless some geometry restriction requires the use of unequal-leg fillet welds. In these few cases, both leg dimensions, separated by a multiplication sign, are placed to the left of the fillet weld symbol. The order of the leg dimensions is not significant and the orientation of the weld must therefore be shown on the drawing.

In contrast to groove-type welds, fillet welds do not always extend for the full length of the joint. The length of a fillet weld, which has a length less than the length of the joint, is specified by placing the required dimension to the right of the fillet weld symbol. If the exact location of such a weld is critical, dimension lines, hatching, or detailing is necessary. The omission of a length dimension, of course, specifies a fillet weld for the full length of the joint.

Also, in contrast to groove welds, fillet welds are often specified as intermittent welds, meaning they are not continuous welds. For an intermittent weld, the segment length dimension is placed to the right of the fillet weld symbol, followed by a hyphen and pitch dimension. The pitch is the distance between centers of segments on one side of the joint.

Intermittent fillet welds can be specified on both sides of a joint by placing a fillet weld symbol both below and above the reference line. Intermittent fillet welds with the segments directly opposite across the joint are called chain intermittent fillet welds. If the segments of intermittent fillet welds are to be staggered in a symmetrical manner on both sides of a joint, the sequence of fillet size, fillet weld symbol, segment-length dimension, multiplication sign and the pitch dimension are offset, left to right, on one side of the reference line (Figure 8).

There are also provisions in the American standard for specifying the contours of fillet welds and even the method by which the contours are to be produced. As with groove welds, these details are best controlled through a shop standard.

Non-North American Company StandardsIncreased interaction between domestic and non-North American companies has led to more frequent interpretation of drawings away from their country of origin. Fortunately, the American standard has included metric dimensions along with U.S. customary units for many years, which should minimize any associated problems.

The ISO standard for welding symbols, though very similar to the American standard, has some differences. The ISO standard provides for the specification of a fillet weld size as either the leg dimension (as with the American standard) or the throat dimension. Since with equal-leg fillet

welds, the throat dimension is approximately 70 percent of the leg dimension, it is essential that this potential difference be recognized. Also, the ISO standard locates the pitch dimension of intermittent welds in the same location specified by the American standard. However, the pitch dimension, by definition of the ISO standard, is the clear distance between segments rather than the distance between centers of segments.

Brazing SymbolsBrazing symbols are similar to those used to specify welds. An arrow, reference line, and tail are used in the same way they are used in welding symbols. Because of the resulting mechanical properties, square- and scarf-groove symbols are more appropriate than the other groove symbols. The root opening or gap is also much more emphasized in brazing symbols compared to symbols specifying fusion welds. The approved WPS may be referenced in the tail of the brazing symbol. Current industry practices rely more on detail drawings to specify brazing applications than the use of brazing symbols.

Nondestructive Examination SymbolsThe arrow, reference line, and tail used to specify a nondestructive examination (NDE), appear exactly the same as those used to specify welds and have the same significance. The various examination methods have been assigned designation letters which are placed below, above or both below and above the reference line to specify, respectively, examination on the "arrow side," "other side" or both sides of the part. Combinations of examinations may be specified by adding additional designation letters with an additional sign separating the methods. In those cases where there is no arrow or other side significance, or there is no preference from which side the examination is made, the designation letters are centered on the reference line.

The approved NDE procedure may be referenced in the tail of the NDE symbol. There is a provision that allows the number of examinations to be specified, and the field-examination and examine-all-around symbols may also be used.

DEFINITION OF QA/QCQuality Control (QC) is a system of routine technical activities, to measure and control the qualityof the inventory as it is being developed. The QC system is designed to:(i) Provide routine and consistent checks to ensure data integrity, correctness, andcompleteness;(ii) Identify and address errors and omissions;(iii) Document and archive inventory material and record all QC activities.QC activities include general methods such as accuracy checks on data acquisition andcalculations and the use of approved standardised procedures for emission calculations,measurements, estimating uncertainties, archiving information and reporting. Higher tier QCactivities include technical reviews of source categories, activity and emission factor data, andmethods.Quality Assurance (QA) activities include a planned system of review procedures conducted bypersonnel not directly involved in the inventory compilation/development process. Reviews,preferably by independent third parties, should be performed upon a finalised inventory followingthe implementation of QC procedures. Reviews verify that data quality objectives were met,ensure that the inventory represents the best possible estimates of emissions and sinks given thecurrent state of scientific knowledge and data available, and support the effectiveness of the QCprogramme.Before implementing QA/QC activities, it is necessary to determine which techniques should be used, and whereand when they will be applied. There are technical and practical considerations in making these decisions. Thetechnical considerations related to the various QA/QC techniques are discussed in general in this chapter, andspecific applications to source categories are described in the source category-specific good practice guidance inChapters 2 to 5. The practical considerations involve assessing national circumstances such as availableresources and expertise and the particular characteristics of the inventory. The level of QA/QC activities shouldbe compatible with the methods or tiers used to estimate emissions for particular source categories. In addition,resources should be focused on priority areas, such as the key source categories (

Depending on the type of metal, sometimes it is necessary to preheat the base metal to lessen distortion, to prevent spalling or cracking, and to avoid thermal shock The preheating temperature depends on the car- bon and alloy content of the base metal. In general, as carbon content increases so does the preheating tem- perature. Improper heating can adversely affect a metal by reducing its resistance to wear, by making it hard and brittle, or by making it more prone to oxidation and scaling. To preheat properly, you must know the composi- tion of the base metal. A magnet can be used to deter- mine if you are working with carbon steel or austenitic manganese steel. Carbon steel is magnetic, but be

care- ful because work-hardened austenitic manganese steel is also magnetic. Make sure that you check for magnet- ism in a nonworked part of the austenitic manganese steel. There are other ways to tell the difference between metals, such as cast iron and cast steel. Cast iron chips or cracks, while cast steel shaves. Also, some metals give off telltale sparks when struck by a chisel. In preheating, you should raise the surface tempera- ture of the workpiece to the desired point and then soak it until the heat reaches its core. After wearfacing, cool the work places slowly. TECHNIQUES Where possible, position the workpiece for down- hand welding. This allows you to finish the job quicker and at less cost. The building up and wearfacing of cast iron is not generally recommended because cast iron tends to crack. However, some cast-iron parts that are subject to straight abrasion can be wearfaced successfully. You must preheat these parts to temperatures of 1000°F to 1200°F and then allow them to cool slowly after wear- facing. Peening deposits on cast iron helps to relieve stresses after welding. Welding materials for building up worn parts differ from those used in wearfacing the same parts. Before wearfacing a badly worn part, you must first build it up to 3/16 to 3/8 of an inch of its finished size. The buildup material must be compatible with both the base metal and the wearfacing overlay as well as being strong enough to meet the structural requirements. Also, they must have the properties that enable them to resist cold flowing, mushing under high-compressive loads, and plastic deformation under heavy impact. Without these properties, the buildup materials cannot support the wearfacing overlay. When the overlay is not properly supported, it will span. Many times high-alloy wearfacing materials are deposited on the parts before they are placed in service. The maximum allowable wear is usually no more than two layers deep (1/4 inch) before wearfacing. Try to deposit the wearfacing alloy in layers that are not too thick. Thick layers creates more problems than no over- lay at all. Usually you only need two layers. The frost layer produces an admixture with the base metal; the second forms a wear-resistant surface. In wearfacing built-up carbon-steel parts, maintain high interpass temperatures and use a weaving bead, rather than a stringer bead. (See fig. 7-46.) Limit the thick- ness of a single pass bead to 3/16 inch. Use the same technique for each layer and avoid severe quenching. Deposits made with check on the surface. high-alloy Checking electrodes should reduces residual Figure 7-47.—Comparison between cross-checking and cracking. 7-28

PostweldHeat TreatmentKey Concepts in Welding Engineeringby R. Scott Funderburk

The need for post heating assumes a potential hydrogen cracking problem exists...

Figure 1. Criteria for hydrogen induced cracking (HIC). Welding Innovation Vol. XV, No. 2, 1998residual stresses. Carbon steels are typically held at 1,100 to 1,250°F (600 to 675°C) for 1 hour per inch (25 mm) of thickness.Stress relieving offers several benefits.For example, when a component with high residual stresses is machined, the material tends to move during the metal removal operation as the stresses are redistributed. After stress relieving, however, greater dimensional stability is maintained during machining,providing for increased dimensional reliability.In addition, the potential for stress corrosion cracking is reduced, and themetallurgical structure can be improved through stress relieving. The steel becomes softer and more ductile through the precipitation of iron carbide at temperatures associated with stress relieving.Finally, the chances for hydrogen induced cracking (HIC) are reduced, although this benefit should not be the only reason for stress relieving. At the elevated temperatures associated with stress relieving, hydrogen often will migrate from the weld metal and the heat affected zone. However, as discussedpreviously, HIC can be minimized by heating at temperatures lower than stress relieving temperatures,resulting in lower PWHT costs.Other ConsiderationsWhen determining whether or not to postweld heat treat, the alloying systemand previous heat treatment of the base metal must be considered. Theproperties of quenched and tempered alloy steels, for instance, can beadversely affected by PWHT if the temperature exceeds the temperingtemperature of the base metal. Stress relief cracking, where the componentfractures during the heating process, can also occur. In contrast, there aresome materials that almost always require PWHT. For example, chromemolybdenumsteels usually need stress relieving in the 1,250 to 1,300°F(675 to 700°C) temperature range. Thus, the specific application and steelmust be considered when determining the need, the temperature and time oftreatment if applied, and other details regarding PWHT.The filler metal composition is also important. After heat treatment, theproperties of the deposited weld can be considerably different than the “aswelded” properties. For example, an E7018 deposit may have a tensilestrength of 75 ksi (500 MPa) in the “as welded” condition. However, afterstress relieving, it may have a tensile strength of only 65 ksi (450 MPa).Therefore, the stress relieved properties of the weld metal, as well as thebase metal, should be evaluated. Electrodes containing chromium and

molybdenum, such as E8018-B2 and E9018-B3, are classified according tothe AWS A5.5 filler metal specification in the stress relieved condition. TheE8018-B2 classification, for example,has a required tensile strength of 80ksi (550 MPa) minimum after stress relieving at 1,275°F (690°C) for 1 hour.In the “as welded” condition, however, the tensile strength may be as high as120 ksi (825 MPa). The objective of this article is to introducethe fundamentals of postweld heat treatment; it is not meant to beused as a design or fabrication guide. For specific recommendations, consultthe filler metal manufacturer and/or the steel producer.

When determining whether or not to PWHT, the alloyingsystem and previous heat treatment of the base metal must be considered

The purpose of preheat:-

1. Reduce the risk of hydrogen cracking 2. Reduce the hardness of the weld heat affected zone 3. Reduce shrinkage stresses during cooling and improve the distribution of

residual stresses.

If preheat is locally applied it must extend to at least 75mm from the weld location and be preferably measured on the opposite face to the one being welded.

• Got To The Pre-Heat Calculator

Background To Preheating

When hydrogen diffusing from a solidified weld meets a hard microstructure under a tensile stress a crack is likely!

Hydrogen cracking normally occurs in the heat affected zone where hard microstructure is to be found, occasionally it can occur in weld metal.

HydrogenThis is a very searching gas that can be liberated by oil, grease, rust etc. and water under the right conditions.

The greatest risk comes from hydrogen generated within the arc from damp or contaminated welding consumables, mainly fluxes or electrode coatings.

Contamination on the parent metal can also be a risk unless the heat from the welding arc can drive it away. Moisture from condensation on the parent metal will normally be driven off by the heat from the arc before it can get into the weld pool.

Hydrogen in the atmosphere is unlikely to penetrate the arc envelope unless welding is carried out in very damp and humid conditions.

A hydrogen crack can take anything from a few hours to 24 hours to occur. After 24 hours cracking is still possible but less likely, although there have been some reported cases of cracking at 72 hours. It is therefore good practice to allow at least 48 hours before carrying out any NDE.

Hydrogen will eventually disperse from the parent metal, within a few days at room temperature or a few hours if held at around 200°C.

Hydrogen cracking is only possible at room temperature, this is why it is also referred to as cold cracking

Parent MetalA hydrogen crack requires a hard microstructure which is created by a hardenable material subject to fast cooling from 800°C to 500°C. Cooling can be slowed down by:-

• applying preheat, • maintaining a high interpass temperature, • increasing welding power and reducing travel speed.

The heat sink caused by the parent metal thickness and the number of available paths the heat can take to escape, also influence cooling rate. (However once the heat sink reaches a certain size further increases have a negligible effect on cooling rate.). This is why when determining preheat the term combined thickness is used, for a butt weld it is twice the thickness of the parent material and for a T fillet weld three times the thickness.

The hardening of a carbon manganese steel/low alloy steel is influenced primarily by carbon content and to a lesser extent other constituents such as manganese, chrome, silicone etc.

The Carbon Equivalent is a formula used to express the harden-ability of a particular alloy steel in terms of an equivalent plain carbon steel. Several such formula exist, the one favoured for low alloy steel is the IIW formula:

CEIIW = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15

Current steel specification do not restrict or limit the Carbon Equivalent and as most steel specs permit a wide range of composition it is possible that one batch of steel may require pre-heat and another may not.

Very low sulphur ( < 0.015%) will increase hardening and special precautions are required when determining the minimum preheat level. Additions of niobium also require special consideration.

For welds subject to high restraint more preheat is advisable (suggest, Increase CE by 0.3 or go down one hydrogen scale).

EN1011 Part 2 (English version available from British Standards)This standard is highly recommended as it gives details on this preheat method and also includes methods covering fine grain and creep resisting steels. It also includes practical guidance on the avoidance of other

cracking mechanisms. Much of the data contained in this standard comes from TWI research tempered by practical experience from industry. (It replaces BS5135)

Welding Steels Without Hydrogen Cracking. http://www.woodhead-publishing.com/ This book is based on the original research work carried out by TWI. It covers the avoidance of hydrogen cracking and preheat in great detail. The preheat graphs tend to require a higher preheat than the equivalent ones in EN1011.

The Welding of Structural Steels Without Preheat The Welding Journal April 2000A very informative article covering recent TWI research into welding low hardenability steels without preheat. The article won the Lincoln arc welding foundation gold award.

Preheat calculator Lincoln arc welding foundationA simple to use and inexpensive calculator. It is based on practical experience and tends to be very conservative when compared with the TWI method.

Welding Calculations

For more information on Mohrs Circle got to efunda.com

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Production Sequence 1. Clean weld and 25mm borders to bright metal using approved solvent.2. Position items to be welded ensuring good fit up and apply purge3. Tack weld parts together using TIG, tacks to at least 5mm min length4. Deposit root run using 1.2mm dia. wire.5. Inspect root run internally6. Complete weld using 1.6mm dia wire using stringer beads as required.7. 100% Visual inspection of completed weld

These symbols are based on the old British Standard, BS499. They are very similar, if not identical, to the American Welding Society standard. The European Standard EN22553 is similar except that it has a dotted reference line which allows the welding symbol to be drawn either way up, see example below.

Click For Further details of AWS welding symbols:-

Further details of AWS welding symbols:-

• A useful PDF file can found at www.aws.org

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Last Modified 15 July 2001