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Welding Symbols Explained
In the complex world of metal fabrication and welding, communication is crucial in ensuring precision and consistency. Welding symbols are a universal language of lines and figures that serves as a vital communication tool between engineers, designers, and welders.
These seemingly cryptic symbols convey vital information about joint types, dimensions, and welding techniques, bridging the gap between design intent and real-world execution. Therefore, unraveling the enigma of welding symbols enhances collaboration and guarantees the structural integrity and quality of welded components.
In this article, we'll delve into the fundamental concepts behind welding symbols, deciphering their meanings and empowering both novices and professionals in welding interpretation.
What are the welding symbols, and why are they so important?
Welding symbols are graphical representations used in engineering and manufacturing to communicate essential information about welds and welding processes. These symbols are standardized and universally understood, allowing engineers, designers, and welders from different backgrounds and locations to effectively communicate and understand the requirements for weld joints and connections.
For engineers and designers, these symbols help specify the type of weld required, the dimensions of the weld, and any other necessary information, ensuring that the design intent is accurately translated into the final product. On the other hand, you, as a welder, rely on these symbols to understand how to perform the weld, which welding techniques to use, the required filler material, and the acceptable tolerances. This standardized communication minimizes errors, reduces rework, and ensures consistent quality across different projects.
Location Of The Elements Of A Welding Symbol
A welding symbol can be a pretty complex drawing that consists of basic weld symbols and supplementary symbols, numbers, and letters that can define every single aspect of a specified weld. Therefore, you can get a weld symbol that seems messy and needs clarification. However, each element of the welding symbol has its specified location and meaning, and you can see it illustrated in the picture below.
As a beginner, this may still seem confusing, so we will go through each element of the welding symbol. We'll be going back to this picture as a reference for future explanations, so try to remember the elements you've seen here.
Structure Of Basic Welding Symbol
The basic form of a welding symbol consists of three vital elements, including the following:
- arrow,
- reference line,
- tail.
These three elements are the most straightforward representation of a welding symbol, and each has a unique role that affects the finished weld, so let's closely explain what they mean and do.
The arrow
The arrow is a crucial element of the welding symbol, connecting the reference line to the joint. The arrow points to the location where the weld is to be applied. If you have been around blueprints, the arrow may look a lot like a leader line.
Simply put, you should consider an arrow as a pointer representing a "Weld here!" sign. As long as the weld is carried out at the specific joint location, even if the weld symbols call for multiple weld passes, there is always only one arrow in the weld symbol.
Source: https://www.weldingandndt.com/welding-symbols-part-1/
Reference line
The reference line is the horizontal line that serves as the anchor for all welding symbols and elements. The reference line is a simple line that carries vital information such as the joint design, the weld pattern, the weld size, etc. This info is handy when each side comes with different joint details. Also, it helps to diminish the usage of too many welding symbols in one joint.
Simply put, consider a reference line as a blank notebook line that designers use to illustrate their thoughts on joint design, required weld process, size of the weld, angle of bevel, size weld profile, depth of penetration, number of welds, spacing, and more. Instead of words, they will use a series of welding symbol elements to help you understand what they are expecting from your weld.
Besides the information, the reference line carries information about the side of the weld. If the engineering drawings call for multi-process weld operation, you'll see multiple reference lines that may contain different data for each weld pass. In the multi-pass symbol, the line closest to the arrow line is considered a first operation or first pass, while each above calls for the following operations.
The Tail
The tail is the last part of the welding symbol, which is drawn at the end of the reference line opposite the arrow. The tail is used to provide welders with additional information for which there is no provision elsewhere. For example, a welding engineer can use the tail to provide supplementary information about the required welding process, the reference document, the electrode, or the examination process.
Even though the tail is the structural part of the welding symbol, it is reserved for supplementary information, so it is often omitted from the drawing. If the required weld is straightforward, the engineer can omit the tail so it doesn't cause confusion on the already complex welding symbol.
The Orientation Of The Weld
When we talked about the reference line, we noted it can also carry information about the side of the weld. The information above or below the reference can represent the location or the side of the joint on which the weld is carried out. Understanding the difference between the two sides is important because even if you create sound and successful welds, you might've been doing them on the wrong side of the joint.
If the information is written below the reference line or on the arrow side of the weld symbol, the weld is carried out on the side of the joint at which the arrow points. If the information is written above the reference line, the weld is carried out on the opposite side of the joint, not on the side where the arrow is pointing. Engineering drawings sometimes call for welds on both sides of the weld metal piece so that you will see information written on both sides of the reference line.
In specific situations, engineers can request that you weld all around the piece. In that case, they will provide the information on the arrow side of the reference line and use the weld all-around supplementary symbol. If the weld side is not important, the element will be placed on top of the reference line.
Numbers In The Welding Symbols
The numbers play a crucial role in weld symbols, as they can highlight various information about the size or length of the weld, number of welds, angle of bevel opening, size of the root, spacing, and much more. The role of the number will depend on a specific location in the weld symbol, so to closely understand them, you'll need to consult the first picture in our blog, which represents the location of the elements of the weld symbols.
The number placed nearest to the tail of the weld symbol (S) represents the size of the weld, depth of bevel, or strength for certain welds. These dimensions are very important because they are directly responsible for the joint’s ability to withstand the needed load. Next to it, or between the size of the weld and the main symbol, the number (E) is used to designate the actual depth of penetration in groove welds,
If the drawing doesn't require welding an entire length of the joint, engineers use numbers between the arrow and the main weld symbol. Closer to the arrow, the number (P) represents the pitch or spacing between the welds (center to center) if welders use multiple welds across one joint. The number (L) represents the length of the weld.
When using groove welds with root opening, engineers can use numbers to represent the size of the root or the angle of the root. The number closer to the groove weld symbol (R) represents the size of the root or depth of metal filling for plug and slot welds. Below or above groove size (depending on the side of the weld), the number (A) denotes a groove angle. Additionally, a number (N) on the arrow side of the reference line can be used to specify the number of spot, seam, projection, or slot welds.
Types of Welding Symbols
The last part of our equation, called welding symbols, are the primary welding symbols that can be divided into two groups:
- Basic welding symbols
- Supplementary symbols
Source: Turn Your Passion for Welding into Income | YesWelder
Basic welding symbols are located in the center of the reference line, above, below, or in the center of it, and they carry information about joint configuration or specific processes. Keep in mind that these won't represent the required welding process but the weld geometry required to make sound and solid weld.
Basic Welding Symbols
Basic welding symbols are graphical representations used to communicate essential information about welds and welding processes in a standardized and concise manner. They are a fundamental part of engineering drawings, blueprints, and other technical documents. Some of the common basic weld symbols are fillet welds, groove welds, spot welds, projection welds, and more. So let's briefly explain each one of them.
Fillet Weld Symbol
Fillet welds are used to join two pieces of metal at an angle, typically perpendicular or at a 45-degree angle, creating lap joints, corner, and T joints. The fillet weld symbol represents a type of weld joint characterized by its triangular cross-section. As a result, The fillet weld symbol is often depicted as a right-angled triangle.
Source: https://weldguru.com/fillet-weld-symbols/
When making a fillet weld, the weld metal gets deposited in the corner that is formed by the two elements to be joined. The weld then penetrates and fuses with the elements to form a solid joint. A number (S) is usually used to represent the size of the fillet weld. However, if the size of the fillet weld is not even, designers can use two numbers in the form of, e.g., 1/4 X 1/2". Additionally, when making intermittent fillet welds or stitch welds, engineers can add length and spacing (L and P) on a welding symbol reference line.
Groove Weld Symbol
Groove welds are one of the most common designs you'll encounter during your welding career. Groove welds involve filling a prepared groove between two pieces of metal with weld metal. While it is often used to weld edge-to-edge joints, the shape of the groove can vary, and these are represented by specific symbols in welding drawings.
As a result, we are seeing a vast variance of groove welds, including:
- Square groove weld,
- V groove welds,
- Bevel groove weld,
- U-groove welds,
- J groove welds,
- Flare bevel groove weld
- Flare V groove welds
The appearance of the groove is often related to the weld symbol, so in the U-groove weld, the groove is in the shape of the letter U; in the V-groove weld, that's V, and so on. You get the point. However, there are specific differences.
Groove weld symbols can represent both regular and root-opening welds. If your welding drawing only shows the groove angle (A), you should prepare the pieces according to the groove appearance and angle of the opening, but there is no root or spacing between the two pieces. However, when welding significantly thicker parts, an engineer can set the root opening (R), which represents the size of the gap between two pieces you are about to weld.
Additionally, engineers can use numbers (S and E), to specify the depth of preparation and depth of penetration you'll need to ensure when preparing and welding two pieces in groove weld joint design.
Plug Weld And Slot Welding Symbols
Plug and slot welding symbols are used to connect two overlapping pieces. One of these pieces will have holes (plug welds have round holes/slot welds have elongated holes), which are filled with weld metal. Weld metal fills the gaps and penetrates through other pieces, creating a strong bond.
Even though they differ in appearance, the weld symbol that represents plug and slot welds is a rectangle. Due to the nature of these processes, this symbol cannot be represented as weld on both sides.
Numbers in plug and slot welds can be used to determine the size or diameter of the plugs (S), the length of the plug hole (L), the number of plugs or slots (N), and the pitch, or center-to-center spacing between each plug weld or slot weld (P). In specific situations, an engineer can state the depth of filling inside the spot or plug (R).
Spot And Projection Weld Symbols
Spot and projection welds are similar to plug and slot welding, used to weld two overlapping pieces. However, within the arc spot welding method, there is no plug or slot to fill. Instead, the pieces are welded without opening, as the pieces melt due to high heat input into the faying surface.
The spot weld symbols are illustrated as a plain circle that can be centered on the reference line or placed above or under it. When the circle symbol is placed on top of the reference line, the side of the joint is not important, and you can weld whichever piece is easier to get to.
Similar to plug weld, numbers in spot weld symbol can be used to specify the required number of spots, center-to-center spacing, or diameter of spot weld at the contact surface.
Resistance Seam Weld Symbols
Similar to spot welding, resistance seam welding uses the resistance between two overlaying pieces to produce heat and eventually fuse them. However, compared to spot welding, the heat is not concentrated in multiple spots. Instead, the resistance seam weld is carried out in a linear form.
The resistance seam welding, therefore, also uses a circle as a weld symbol, but there are two lines inside the circle (representing the linear form of the weld). Like with spot welding, a circle can be placed above, below, or in the center of the reference line to indicate the location of the weld. The numbers can be used to specify the width and length of the seam weld.
Surfacing Weld symbol
Surfacing welds are commonly used to reinforce a piece or to repair worn-down elements. The welds are applied across the surface. The surfacing can be made using single or multi-pass welds, and the weld symbol is in the shape of two pain half circles, always drawn below the reference line, as the welds are applied to the arrow side of the joint.
The number can be added to the basic surfacing weld symbol to specify the minimal weld size. When welding, the surfacing welds should never be lower than specified.
Backing Weld symbol
Backing is defined as material placed at the root of a weld joint for the purpose of supporting molten weld metal. Its function is to facilitate complete joint penetration. The backing can be permanent or removable, and if it is permanent, it is part of a basic weld symbol illustrated in the form of a pain half circle.
When backing weld is used, numbers are usually not necessary. In addition, backing is usually a part of groove weld symbols, but an engineer can add R to the symbol to note that backing should be removed after welding.
Stud Welding Symbol
Stud Welding is a fast and permanent system for welding metal studs to a metal base. The welds are produced by a standalone unit and are widely used in various applications and workshops. The welding symbol for stud welding is a crossed circle that is strictly placed below the reference line since the welds are always performed on the arrow side of the joint.
Like spot welding, engineers and designers can use numbers to indicate the number of required studs, the spacing between them, and the diameter of studs required to produce solid weld.
Source: https://openoregon.pressbooks.pub/weldsymbols/chapter/chapter-5/
Edge Weld Symbol
The edge weld is a specialized weld that has limited fields of application and is mostly used for the joining of sheet metal components, but it can also be used to join the edges of thin tubes. These welds can be used on a minimum of two sheets being welded on their edge or can be used with multiple sheet metals.
The edge weld symbol is in the shape of two rectangles that illustrate the edges of pieces. Even though edge welds can join multiple edges, the symbols still stay the same. Numbers can be used to specify the depth of penetration or length of the edge weld and spacing in case multiple shorter welds are used.
Source: https://openoregon.pressbooks.pub/weldsymbols/chapter/chapter-7/
Supplementary Symbols
Supplementary symbols, as their name states, are usually used to provide supplementary information about the final product. These elements can be added to elementary symbols to specify the desired finishing, surface shape, or other information.
Field Weld Symbol
Sometimes, usually in pipeline welding, engineers can require that specific welds be carried out in a field. In that case, you will encounter a flagpole symbol (field weld) that is also placed on the intersection of the reference line and arrow line. This is not such a common symbol, and it is usually used due to logistics or other specific reasons.
Melt-thru Weld Symbol
Melt-through is a type of visible root reinforcement produced in a joint welded from one side. This is the penetrated weld metal that extends beyond the base metal on the backside of a joint welded from the opposite side. The symbol is similar to a backing, but in this case, the half circle is filled (black). The engineer can use numbers to specify the height of the weld through reinforcement.
Consumable Insert Weld Symbol
Consumable inserts are another not-so-common supplementary symbol that denotes the inserts that provide the highest quality root pass for welds that require radiography. These are metal strips in special sizes and dimensions that are used for root pass welding with one-side access. The symbol is in the form of a small pain square, and the additional information is usually not required.
Weld All-Around Symbol
As we already noted, in specific situations, an engineer can draw a symbol on a fillet weld that requires welding all around the piece. In that case, a simple supplementary symbol in the form of a circle on a place where the reference line and arrow line intersect is drawn. In the symbol, the designer doesn't use the weld on both sides but rather a separate symbol that means well all around the piece.
Backing/Spacer Weld Symbol
Backing or spacer bars are supplementary symbols in the form of a plain rectangle. The backing is used on the other side of the weld to support the weld or absorb excessive heat, while a spacer is inserted into the root to control the size of the gap.
Contour Weld Symbols
Weld contour is a supplementary symbol that indicates the appearance of the surface of the weld in the end. The surface can be flush, concave, or convex, and this is indicated by a line that is either straight, convex or concave line, placed above the symbol that represents the type of weld or joint configuration.
Finishing Symbols
Finishing symbols are used to explain what finishing method should be used to achieve the desirable and specified weld appearance or contour. The finishing method is specified by a letter placed above the contour symbol and above the reference line. The letters denote the first letter of the finishing method, and these are:
- C = Chipping
- M = Machining
- G = Grinding
- H = Hammering
- P = Planishing
- R = Rolling
- U = Unspecified
Additional Tail Information
As we noted, the tail can be used to provide additional information about the required electrodes, references, or more. Most importantly, an engineer can call for a specific welding process required to produce the specified weld. In that case, letter designation for welding and allied processes is used, and designers use forms such as GMAW, GTAW, or SMAW to call for MIG, TIG, or Stick welding when necessary.
Conclusion
Welding symbols can seem pretty confusing to beginners, and to effectively interpret them, you will need to understand each element of a welding symbol. The most basic ones are the arrow, reference line, and tail. The arrow points to the location of the weld, the reference lines are the foundation of each symbol, and the tail carries additional information.
Engineers and designers provide information through weld symbols, numbers, and letters on top, below, or above the reference lines. The location, shape, or letter of each element of the weld symbol will have different meanings, and we believe our article helped you decipher what each one means.
🧐Welding Symbols Explained - FAQ
1. What are the three vital elements of the basic form of a welding symbol?
The basic form of a welding symbol consists of three vital elements, including the following:
- arrow,
- reference line,
- tail.
These three elements are the most straightforward representation of a welding symbol, and each has a unique role that affects the finished weld, so let's closely explain what they mean and do.
2. What are the common basic weld symbols?
Some of the common basic weld symbols are fillet welds, groove welds, spot welds, projection welds, plug weld and slot welding, groove, surfacing and more.
3. What are groove welds symbols?
Groove welds involve filling a prepared groove between two pieces of metal with weld metal. While it is often used to weld edge-to-edge joints, the shape of the groove can vary, and these are represented by specific symbols in welding drawings. As a result, we are seeing a vast variance of groove welds, including:
- Square groove weld,
- V groove welds,
- Bevel groove weld,
- U-groove welds,
- J groove welds,
- Flare bevel groove weld
- Flare V groove welds
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