How To Read Welding Blueprints 

Thinking of pursuing a career in welding? A great place to start is getting acquainted with welding blueprints by learning welding symbols that guide the welder. Accurately decoding the symbols of a blueprint goes a long way to decide the quality of work done and consequently saves time. In other words, reading blueprints saves costs because projects can be completed in the very first attempt. 

Welding symbols provide the means of accurately explaining welding pieces of information with the use of diagrams, but having a deep understanding of these diagrams is quite complicated, this is why in this article we will make some explanation on that. Just like every other type of drafting, welding also has sets of symbols that help to make it easy to communicate, between the designer and the welder. This blueprint language will look strange at first which is why it is advisable to learn the symbols one at a time so as not to confuse symbols with each other or mix them up when working.

What is a welding blueprint

According to the American Welding Society (AWS), a blueprint is a “technical drawing of an architectural or engineering design” which in wielding refers to symbols that indicate to the welder such necessary information on designs, sizes, locations and other details of construction. Reading and understanding wielding blueprints are similar to the ability of the cartographer to read a map signifying bus routes, geographical landscapes, rivers and oceans, and other terrains. However, how the welder is able to work with the blueprint is heavily reliant on his ability to interpret the symbols accurately. Though not many possess the skill, especially those unaffiliated with the field of engineering, anyone can learn to develop it. Therefore, we shall start from the simple to the complex. 


These are the basic directional and communicational tools used in blueprints. They are of different types representing peculiar meanings to the welder. Some of the common lines, descriptions, and their uses are listed below:

Visible Lines: This is characterized by heavy unbroken lines that indicate visible edges of an object.

Hidden Lines: A direct opposite of visible lines that are broken (medium lines with short evenly spaced dashes) and are used to show concealed objects.

Center Lines: Like hidden lines, center lines are broken but are unevenly spaced dashes. It shows the symmetry of an axis and the location of centers.

Dimension Lines: Dimension lines are thin lines terminated with arrowheads at each end that indicate measured distance.

Extension Lines: These are thin unbroken lines indicating the extent of a dimension usually placed on both ends of the calculated distance.

Break (long): This is a thin and solid line with a zig-zag that is used to reduce the size of the drawing required to space objects or reduce any detail.

Break (short): This break is a thick and solid line that specifies the need to create a space between objects.

Phantom or Datum Line: A medium series of one long dash and too short dashes evenly spaced to end with a long dash. 

Stitch Line: A medium line of short dashes, evenly spaced and labeled used to indicate stitching or sewing. 

Cutting Plane Line: it is simply used to designate where an imaginary cutting took place.

Viewing Plane Line: It indicates the direction of sight from a partial view.

Chain Line: The chain line is used to communicate that a surface or zone needs additional treatment or consideration.

Section Lines: They indicate the surface in a section imagined to have cut along the cutting plane line.

Welding Blueprint Symbols

Taking from the Universal Technical Institute (a group of technical colleges headquartered in Arizona (USA), welding blueprint symbols are communicative links between designers such as an architect, a welding engineer, foreman or supervisor, and the welder. These symbols are likened to shorthand codes that refer the welder to the type of weld, size, processing, and finishing detail. The symbols are incorporated into the blueprint regardless of its form. This means the welding blueprint can be isometric, orthographic, or in 3D. 

Furthermore, the welding symbols exist in different varieties to represent the different types of welds to be done. Though they are not entirely utilized in every industry, the construction industry requires these symbols largely because it requires parts and pieces of objects to meet exact specifications. This is why welders will always rely heavily on blueprints to carry out their jobs. 

Just as there are many types of lines, welding blueprints house a lot of symbols. A standard welding blueprint provides a front, top and rearview, with welding symbols residing in specific areas of the sketch. It is important to learn and memorize all the symbols. However, let us take a quick look at the structure of the welding symbols before plunging into the basic and common symbols the welder should be familiar with.

The structure of the welding symbols is drawn to specifically describe the direction and type of weld to make. Every welding symbol has an arrowhead that points to the location where a weld should be made. An integral part of this structure is the reference line. The reference line, also called the horizontal line, is an important structure of any welding symbol. It secures other welding symbols and serves as an anchor. Every instruction tied to welding on the blueprint is strung along the reference line. An arrow connects the reference line to the joint that is to be wielded. 

Also, there is the tail of a welding symbol which is used to indicate designations where the welder has to engage in the brazing, welding, and cutting process. This is done in complement to the specifications, procedures, and supplementary information laid down in making the weld. This is where the identification of the filler metal and other data are placed in the tail of the welding symbol.

What’s more? Welding symbols may include other elements to convey specific welding information. Welding information can be conveyed in ways such as by drawing notes, specifications, or codes which eliminates the need to include corresponding elements in the symbol. In addition, an important concept for welders to be familiar with is basic welding joint types, which include butt, corner, tee, lap, and edge joints. A joint is an edge or point where two or more plastic or metal pieces are joined together. 

Letters on the Welding Symbols

As capable welders, it is vital to decoding the meaning of letters attached to a blueprint. When you start reading welding blueprints, you will letter attached to the charts. These letters reveal important information to consider when making the welds, such as length and root openings. Here is a reference to use for the letters: 

  • A: Angle of Countersink
  • C: Chipping Finish
  • F: Finish Symbol
  • G: Grinding Finish
  • L: Weldlength
  • M: Machining Finish
  • N: Number of spot welds
  • P: Pitch of Welds (Center-to-Center Spacing)
  • R: Root Opening; Depth of Filling
  • S: Depth of Preparation; Size of Strength
  • T: Specification Process

Needless to say, letters are big parts of the welding specifications. These letters can be found with the welding symbols on the blueprint.

We also have the designation of the welding process using letters 

Gas welding

Oxyhydrogen welding- OHW

Pressure gas welding- PGW

Air-acetylene welding- AAW

Oxyacetylene welding- OAW

Flow welding

Upset welding- UW

Percussion welding- PEW

Flash welding- FW

Induction welding- IW

Resistance welding- RW


Dip brazing- DB

Block brazing- BB

Induction brazing-

Flow brazing- FLB

Torch brazing- TB

Furnace brazing- FB

Twin carbon arc brazing- TCAB

Forge welding

Die welding- DW

Hammer welding- HW

Roll welding- RW

Arc welding

Flux corded arc welding- FCAW

Gas carbon arc welding- GCAW

Gas metal arc welding- GMAW

Stud welding- SW

Submerged arc welding- SAW

Atomic hydrogen welding- AHW

Bare metal arc welding-  BMAW

Twin carbon arc welding- TCAW

Gas tungsten arc welding- GTAW

Shielded metal arc welding- SMAW

Carbon arc welding- CAW

Gas shielded stud arc welding- GSSW

Shielded metal arc welding- SMAW

Thermit welding

Pressure thermit welding- PTW

Non-pressure thermit welding- NTW

Methods of applying the above processes welding symbols

Manual welding- MA

Automatic welding- AU

Semi-automatic welding- SE

Machine welding- ME

The cutting process is also assigned with letters

Metal powder cutting- POC

Oxygen cutting- OC

Arc cutting- AC

Carbon arc cutting- CAC

Arc oxygen cutting- AOC

Metal arc cutting- MAC

Chemical flux cutting- FOC

Air carbon arc cutting- AAC

The method of applying the above processes are also written in these form

Machine cutting- ME

Manual cutting- MA

Automatic cutting- AU

Semii automatic cutting- SA


Symbols may be used without specifications, reference and process if

The welding procedure to be used has already been described somewhere else like in a process sheet or in a shop instruction or better still when a note similar to words like ‘unless otherwise designated, all welds are to be made in accordance with specification number’ appears on the drawing. Also when no specification process or reference is used with a welding symbol then the tail may be omitted. General notes might also be placed on the drawings to provide detailed information relating to the predominant welds and these pieces of information may not be repeated on the symbols. When the use of a definite process is required these processes may be indicated with the use of letter designations explained above. When it comes to locating weld symbols they are shown only on the welding symbol reference line and not on the lines of drawing except the resistance seam and the resistance spot.

Dimensions and Angles

The angles and dimensions of the welding symbol are very important to note as they make it easier to understand the welding blueprint. The blueprints are packed with a lot of details that are captured in very few words. It takes an experienced blueprint reader to decode They can be used to communicate length, width, depth, and the opening of the weld. Meanwhile, the diameter or width of the weld is generally noted on the left of the welding symbol and will be written down as a fraction in inches. The length also expressed in inches, is written on the right of the weld symbol.

Weld Types

The very first point of call is to know to understand the different types of welds and the symbols that represent them on the blueprint. Each welding position has its symbol placed at the center of the reference line. At this point, a geometric shape or two parallel lines can be placed to aid in identifying what type of weld should be performed on the metal. This is called the weld symbol (not to be confused with the overall welding symbol ). 

When reading a blueprint, one must pay close attention to the placement of the symbol on the reference line. If the welding symbol is present below the reference line, the weld should be carried out on the arrow side of the joint. On the other hand, if the welding symbol is present on top of the reference line on the diagram, the weld should be made on the opposite side of the joint from where the arrow is pointing. If the weld symbol is noted on both sides of the reference line, then multiple welds must be made on both sides of the joints.

 Among the different types of weld, here are six basic types we have fillet, groove, plug and slot weld, spot weld, seam weld, and stud weld.


This is one of the most recognized weld symbols. It is used to make lap joints, corner joints, and T-joints. Though not always appearing as an isosceles or right-angle triangle, it comes into view as a triangle. A small quantity of welding metal is deposited in the corner of the joint formed by the two members. It penetrates and fuses with the material of the frames to form the joint.


A groove weld is a weld on a blueprint between edges and surfaces. It is commonly used to make an edge to edge joints and often used in corner joints, T joints, and joints between curved and flat pieces. Groove welds are made of an arrow line, reference line, a tail, weld procedure specification (which is a document that gives direction to the welder by providing information such as material thickness, the general position the part needs to be welded in, the electrodes to use and more), and a groove weld symbol. It is considered more complicated than the fillet weld symbol, and can also be combined with it. 

There are varieties of groove weld symbols and that suggests many ways to have a groove weld which are differentiated by the preparation of the edges to be joined and its dimensional shape. There are types of groove welds such as Square groove, V-groove, Bevel groove, U-groove, J-groove, Flare V-groove, and Flare Bevel groove. 

Plug and slot welds

Welders use plug and/or slot weld to connect overlapping parts by drilling holes through one of them (round for plug welds, elongated for slot welds). In this case, weld metal is deposited in the holes to penetrate and fuse with the base metal of the two parts in order to form the joint. 


This type of weld connects overlapping pieces of metal by applying pressure and using electricity. To do this, electrodes are brought to the parts to be joined before the pressure is applied; afterward, electricity is applied to melt the metal leaving the electrodes to help solidify the material. 

Seam Weld

A seam weld uses a similar process to a spot weld. Seam welding is the art of welding two materials using the heat generated from electrical resistance. The weld projects through the top surface and melts into the other part with the help of heat. The process is mostly used on metals since they conduct electricity easily and can sustain relatively high pressures.

Stud Welds

This is mostly practiced by many store owners. It is a fast, reliable, and accurate welding method. Here, a metal stud is joined to a metal piece and heated with an arc. The equipment required for stud welding is composed of the following:

A direct current Power Supply

A Controller

A Weld Gun

Cables to tie the system components and base metal together

In most systems, the power supply and controller are combined as one component called the “Welder”.


When it comes to welding, it is quite important to be able to read welding symbols really well. You cant understand how welding works without reading the blueprints

As a new entrant into welding construction, you may find it difficult to read and understand how the blueprints work. Sometimes, the drawings are too complicated and confusing, even for experts. It takes time, practice, and patience to learn how to read them.

Once you master the basic of welding you will be ready to learn and understand the so many other drawings and symbols on blueprints and shop drawings


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