Weld: introduction, properties, and its functions

the weld

Weld refers to joining pieces of metal together by heating them, with or without pressing.


A weld is defined as a union of metals by welding, due to heat, and or pressure.

BS 499-1:1991
weld profile


The following terms include in a weld property:

Size, and shape, the width of the bead, throat dimension, height and width of the shape, and weld area. etc.

weld beads


Weld bead

beads have a greater impact on the quality of a sound joint. In terms of the properties of a joint, bead geometry has considerable parameters that can alter the mechanical properties of a welded joint. 

Further information >>>weld bead and its properties

Face is the surface of the fusion weld on that side where the welding forms.

weld profile

Leg is The distance from the root of the joint to the weld toe.

Welding toe is the interface of the base metal and weld metal.

Heat affected zone

The part of the base metal that is close to the weld metal and which has not been melted but whose mechanical properties or microstructure changed by the effect of heat is called the heat-affected zone.

Types of weld

According to BS standard, it can be classified as follows:

  • Buttweld:(but weld can be configured in a:)
    • butt joint
    • T joint
    • corner joint
  • Fillet
  • Slot
  • Plug
  • Autogenous

Further information >>>Preparation of welding joints

Weld terms


Preparation of Joints

Root Opening: A separation between workpieces at the root area of the joint.

Root Face: portion of the groove face adjacent to
the joint root.

Groove Face: the surface of the joint members included in the groove.

Bevel Angle: the angle formed between the prepared
edge of a member and a plane perpendicular to the surface of the member

Groove Angle: The total included the angle of the groove between workpieces.

Groove Size: The size of joint penetration of a groove weld.

Weld discontinuities

Welding defects that impede the continuity of the weld metal and base metal, come under the category of welding discontinuities. These types of welding defects can occur in different parts of the metal which can be described as follows:

Related to the welding process

  • Geometric
    • Misalignment
    • Undercut
    • Concavity
    • Convexity
    • Overlap
    • Burn-through
    • Incomplete penetration
    • Shrinkage
    • Surface irregularity
  • Other
    • Slag inclusion
    • Oxide films
    • Spatters
    • Arc craters


  • Cracks or Fissures
    • Hot cracks
    • Cold crack
  • Porosity
    • Spherical
    • Elongated
    • Worm-hole
  • Microstructure alternation
  • Weld metal and (HAZ) segregation.
  • Base plate laminations.

Related to design

  • Changes in section and other stress concentrations
  • Joint types

Further information >>> Welding Defects

Absorption of gases

Absorption of gases can cause a significant metallurgical change in the formation of molten metal. The gases may react with the molten welds and with each other. Gases such as hydrogen, nitrogen, and oxygen are the most frequently absorbed in molten metal.


welding symbols

Symbols are used to indicate the welding location, length, termination, and a good deal of other information.

Further information >>> Welding symbols

The information on theweldings.com is published in good faith and for educational purposes only.

References: API577, BS 499-1:1991