Kinds of welds

Types of Welds

In structural welding procedure, a backing plate may be attached to the back side of joint to stop the through-flow of molten metal. In contrast, in pipe welding, an opening between the two sides is usually left that way, allowing the welder to weld through to the back and leave a weld bead on the outside.

With these different objectives in mind, there are six basic types of welds below:

Groove Weld

Groove welding is a reference to the type of joint being prepared. There are different ways to prepare a groove for welding. “V-groove” is a common one with plates butted together forming a kind of “v” shape, this can be at multiple angles. Some may be prepared at specific gaps, with or without lands. There are also “U-groove” (often mad with a air carbon arc gouge), and “J-groove” (half a ‘U-groove’ and half 90 degree edge, or butt). Researching welding symbols may help you out, each groove or any other joint has a specific welding symbol on a drawing.  In any case, no matter the type of joint, the cleaner, the better.

Tack Weld

Tack welding is a major part of welding which are used as a temporary means to hold the components in the proper location, alignment, and distance apart, while welding.

The engineers use high heat input process for the welding and the tack is applied by the shielded metal arc welding process. The tack is a very rapid quench application and a brittle, crack sensitive micro structure results usually at the root of the weld.

Seam Weld

A weld made by arc seam or resistance seam welding where
the welding process is not specified.  This term infers resistance seam

Multipass Weld

Multipass welding is often employed with the submerged arc process. When plate thicknesses exceed the limitation of two pass techniques, or whereinability to provide accurate joint fit-up prevents the use of highcurrent – multiple pass submerged arc welding should be used.Where possible a split pass procedure as shown in Figure 39 should be used to allow easy flux removal andto prevent weld cracking. Each weld pass should be slightly convex as shown to assist in slag removal andpreventing weld cracking.

Multipass welding procedures also enable a variety of weld joints and plate thicknesses to be welded withthe same procedures and materials. In certain base materials, the multiple pass welding technique must beused to maintain adequate properties in the base HAZ.An example of the use of the multiple pass technique for joints which present difficult alignment problems . For pressure vessel circumferential welds such as head-to-shell and shell butts, this doublebevel plate preparation with semiautomatic or automatic Mig used to handle varying fit-up in the root area isan excellent combination procedure. Fill passes are then welded with submerged arc to provide consistentquality low cost welds. The gas metal-arc welding process is the best choice for manual or automatic root orfirst pass procedures. The resulting weld metal is free from internal slag and external slag is minimal makingthe subsequent submerged arc welds free from defects.For welding plates above two inches thick, multipass procedures must be used. Figures 41 and 42 provideexamples of joint preparation and both single and two wire welding conditions for thick plates.Welding flux and wire must be selected with multipass procedures in mind. Control of weld chemistry isespecially important to insure crack free deposits.

Spot Weld

A spot weld is a weld made by arc spot or resistance spot welding where the welding process is not specified. This term infers a resistance spot weld.

Upset Weld

A weld made by upset welding. An upset weld is a resistance welding process where fusion occurs progressively along a joint of over the entire abutting surface. The application of pressure before heating is required and occurs during the heating period. Heat comes from the resistance to the flow of electric current in the area of contact between the surfaces.

Plug Weld

plug weld is used to fasten two pieces of metal together using a welder. When joining the pieces, a hole is drilled into the top piece and it is laid over the bottom one. A weld is then made by running a bead inside of the drilled hole, thereby holding the two pieces together. When doing auto body repair, this type of weld is often used when replacing body panels. The finished result resembles a spot weld in that it is circular.

When joining two dissimilar thicknesses of metal, the plug weld is often the weld of choice. By welding the thin top piece to a thicker bottom piece, a strong weld can be produced. While this type of weld is occasionally used to connect two thick sheets of steel together, it is primarily a thin metal weld. When making one, welders need tobe careful not to burn through the bottom piece of metal.

The weld is also used when welding a rod inside of a pipe. When the fit is such that the rod or bolt stud fits snugly inside of a hollow tube, a hole is drilled into the tube and a plug weld is used to secure the rod inside of it. Occasionally, this method is also used when welding thin exhaust pipes onto a vehicle. Once the exhaust sections are installed, the pipe is welded using this method to secure the system underneath the vehicle.

Slot Weld

This is a weld made in an elongated hole in one member of a lap or
tee joint joining that member to the surface of the other member that is
exposed through the hole.

This hole may be open at one end and may be partially or completely filled with weld metal.

NOTE: A fillet welded slot does not conform to this definition.

Surfacing Weld

These are welds composed of one or more strings or weave beads
deposited on an unbroken surface to obtain desired properties or

This type of weld is used to build up surfaces or replace metal on worn surfaces. It is also used with square butt joints.

Fillet Weld

A fillet weld joins two surfaces at an approximate right angle to each other. There are several types of fillet weld:

  • A full fillet weld is a weld where the size of the weld is the same as the thickness of the thinner object joined together.
  • A staggered intermittent fillet weld refers to two lines of intermittent welding on a joint. An example is a tee joint (see below) where the fillet increments that are in one line are staggered in comparison to the other line.
  • Chain Intermittent Fillet Weld: Refers to two lines of intermittent fillet welds in a lap joint or T where the welds in one line are approximately opposite those in the other line.

Other terms associated with fillet welds include:

  • Boxing which refers to the continuation of a fillet weld around a corner of a member. It is an extension of the principal weld.
  • Convexity: Refers to the maximum perpendicular distance from the face of a convex fillet weld to a line joining the toes.

Flash Weld

A weld made by flash welding. Flash welding is referred to as a resistance welding process where fusion is produced over the entire abutting surface. Heat is created by the resistance to the current flow between two surfaces and by the application of pressure after heating is mostly complete. Flashing is accompanied by the expulsion of metal from the joint.