Terms and definitions that describe the many aspects of welding are described and shown in the many diagrams below.
Guidelines for weld placement and electrode selection based on material thickness and welding position are in the tables below as well.
Nomenclature of Welds
- Fusion Zone (Filler Penetration): The fusion zone is the area of base metal melted as determined in the cross section of a weld.
- Leg of a Fillet Weld: The leg of a fillet weld is the distance from the root of the joint to the toe of the fillet weld. There are two legs in a fillet weld.
- Root of the Weld: This is the point at which the bottom of the weld intersects the base metal surface, as shown in the cross section of weld.
- Size of the WeldEqual leg-length fillet welds: The size of the weld is designated by leg-length of the largest isosceles right triangle that can be scribed within the fillet weld cross section.Unequal leg-length fillet welds: The size of the weld is designated by the leg-length of the largest right triangle that can be inscribed within the fillet weld cross section.
Groove weld: The size of the weld is the depth of chamfering plus the root penetration when specified.
- Throat of a Fillet WeldTheoretical throat: This is the perpendicular distance of the weld and the hypotenuse of the largest right triangle that can be inscribed within the fillet weld cross section.Actual throat: This is distance from the root of a fillet weld to the center of its face. f. Face of the Weld. This is exposed surface of the weld, made by an arc or gas welding process on the side from which the welding was done.
- Toe of the Weld: This is the junction between the face of the weld and the base metal.
- Reinforcement of the Weld: This is the weld metal on the face of a groove weld in excess of the metal necessary for the specified weld size.
Glossary for Heat Affected Zones in Multipass Weld
The nomenclature of the weld, the zones affected by the welding heat when a butt weld is made by more than one pass or layer, and the nomenclature applying to the grooves used in butt welding are shown in figure 6-14.
Figure 6-15 is based on weld type and position.
The primary heat zone is the area fused or affected by heat in the first pass or application of weld metal.
The secondary heat zone is the area affected in the second pass and overlaps the primary heat zone.
The portion of base metal that hardens or changes its properties as a result of the welding heat in the primary zone is partly annealed or softened by the welding heat in the secondary zone.
The weld metal in the first layer is also refined in structure by the welding heat of the second layer.
The two heating conditions are important in determining the order or sequence in depositing weld metal in a particular joint design.
Welding Position Diagram
Flat, Horizontal and Flat Weld Position Chart
Vertical Down and Overhead Weld Position Chart for Welds Under 1″
Flat and Horizontal Position for Welds 1″ or Larger
Welding Positions for Materials Over 1 Inch
Types of Welding Joints
Welding is a materials joining process used in making welds.
A weld is a localized coalescence of metals or nonmetals produced either by heating the materials to a suitable temperate with or without the application of pressure, or by the application of pressure alone, with or without the use of filler metal.
Coalescence is a growing together or a growing into one body, and is used in all of the welding process definitions.
A weldment is an assembly of component parts joined by welding, which can be made of many or few metal parts.
A weldment may contain metals of different compositions, and the pieces may be in the form of rolled shapes, sheet, plate, pipe, forgings, or castings.
To produce a usable structure or weldment, there must be weld joints between the various pieces that make the weldment.
The joint is the junction of members or the edges of members which are to be joined or have been joined.
Filler metal is the material to be added in making a welded, brazed, or soldered joint.
Base metal is the material to be welded, soldered, or cut.
The properties of a welded joint depend partly on the correct preparation of the edges being welded.
All mill scale, rust, oxides, and other impurities must be removed from the joint edges or surfaces to prevent their inclusion in the weld metal.
The edges should be prepared to permit fusion without excessive melting. Care must be taken to keep heat loss due to radiation into the base metal from the weld to a minimum.
A properly prepared joint will keep both expansion on heating and contraction on cooling to a minimum.
Preparation of the metal for welding depends upon the form, thickness, and kind of metal, the load the weld will be required to support, and the available means for preparing the edges to be joined.
Butt Joint Diagram
This type of joint is used to join the edges of two plates or surfaces located in approximately the same plane.
Plane square butt joints in light sections are shown in figure 6-17.
But Joints in Heavy Sections
Grooved butt joints for heavy sections with several types of edge preparation are shown in figure 6-18.
These edges can be prepared by flame cutting, shearing, flame grooving, machining, chipping, or carbon arc air cutting or gouging. The edge surfaces in each case must be free of oxides, scales, dirt, grease, or other foreign matter.
b. The square butt joints shown in figure 6-16 are used for butt welding light sheet metal. Plate thicknesses 3/8 to 1/2 in. (0.95 to 1.27 cm) can be welded using the single V or single U joints as shown in views A and C, figure 6-18.
The edges of heavier sections (1/2 to 2 in. (1.27 to 5.08 cm)) are prepared as shown in view B, figure 6-18.
Thickness of 3/4 in. (1.91 cm) and up are prepared as shown in view D, figure 6-18. The edges of heavier sections should be prepared as shown in views B and D, figure 6-18.
The single U groove (view C, fig. 6-18) is more satisfactory and requires less filler metal than the single V groove when welding heavy sections and when welding in deep grooves.
The double V groove joint requires approximately one-half the amount of filler metal used to produce the single V groove joint for the same plate thickness.
In general, butt joints prepared from both sides permit easier welding, produce less distortion, and insure better weld metal qualities in heavy sections than joints prepared from one side only.
Corner Joints for Sheets and Plates
The common corner joints are classified as flush or closed, half open, and full open. This type of joint is used to join two members located at approximately right angles to each other in the form of an L.
The fillet weld corner joint (view A, fig. 6-19) is used in the construction of boxes, box frames, tanks, and similar fabrications.
The closed corner joint (view B, fig. 6-19) is used on light sheet metal, usually 20 gage or less, and on lighter sheets when high strength is not required at the joint.
In making the joint by oxyacetylene welding, the overlapping edge is melted down, and little or no filler metal is added.
In arc welding, only a very light bead is required to make the joint.
When the closed joint is used for heavy sections, the lapped plate is V beveled or U grooved to permit penetration to root of the joint.
Half open comer joints are suitable for material 12 gage and heavier.
This joint is used when welding can only be performed on one side and when loads will not be severe.
The open corner joint (view C, fig. 6-19) is used on heavier sheets and plates.
The two edges are melted down and filler metal is added to fill up the corner.
This type of joint is the strongest of the corner joints.
Corner joints on heavy plates are welded from both sides as shown in view D, figure 6-19.
The joint is first welded from the outside, then reinforced from the back side with a seal bead.
Edge Joints for Light Sheets and Plates
This type of joint is used to join two or more parallel or nearly parallel members.
It is not very strong and is used to join edges of sheet metal, reinforcing plates in flanges of I beams, edges of angles, mufflers, tanks for liquids, housing, etc.
Two parallel plates are joined together as shown in view A, figure 6-20.
On heavy plates, sufficient filler metal is added to fuse or melt each plate edge completely and to reinforce the joint.
b. Light sheets are welded as shown in view B, figure 6-20. No preparation is necessary other than to clean the edges and tack weld them in position.
The edges are fused together so no filler metal is required. The heavy plate joint as shown in view C, figure 6-20, requires that the edges be beveled in order to secure good penetration and fusion of the side walls.
This type of joint is used to join two overlapping members.
A single lap joint where welding must be done from one side is shown in view A, figure 6-21.
The double lap joint is welded on both sides and develops the full strength of the welded members (view B, fig. 6-21).
An offset lap joint (view C, fig. 6-21) is used where two overlapping plates must be joined and welded in the same plane.
This type of joint is stronger than the single lap type, but is more difficult to prepare.
Single Pass Fillet Weld Tee Joint
Tee joints are used to weld two plates or section with surfaces located approximately 90 degrees to each others at the joint, but the surface of one plate or section is not in the same plane as the end of the other surface.
A plain tee joint welded from both sides is shown in view B, figure 6-22. The included angle of bevel in the preparation of tee joints is approximately half that required for butt joints.
Other edge preparations used in tee joints are shown in figure 6-23.
A plain tee joint, which requires no preparation other than cleaning the end of the vertical plate and the surface of the horizontal plate, is shown in view A, figure 6-23.
The single beveled joint (view B, fig. 6-23) is used on heavy plates that can be welded from both sides.
The double-beveled joint (view C, fig. 6-23) is used heavy plates that can be welded from both sides.
The single J joint (view D, fig. 6-23) used for welding plates 1 in. thick or heavier where welding is done from one side.
The double J joint (view E, fig. 6-23) is used for welding very heavy plates form both sides.
Care must be taken to insure penetration into the root of the weld.
This penetration is promoted by root openings between the ends of the vertical members and the horizontal surfaces