8 Types of Welding Defects (Explained With Visual Pictures)

Types of welding defects
Image credit: The welding master

Types of welding defects are mentioned below along with the visual images.

  1. Incomplete penetration
  2. Lack of fusion
  3. Undercut
  4. Slag inclusion
  5. Porosity
  6. Crack
  7. Spatter
  8. Arc blow

Let me tell you few important things about each type of welding defect one by one.

8 Types of Welding Defects

In any welding operation, the main purpose is to achieve a good defect free welded joints.

But achieving this perfect weld is not so easy.

There are always some small minute slag or other inclusions in the weld which leads to some variations in the properties of the welded joints.

When these inclusions of discontinuity are in more proportion, it is termed as a welding defect.

Reasons for welding defects

  • Welding consumables
  • Lack of cleanliness
  • Unfavorable properties of base metal
  • Insufficient workmanship
  • Wrong welding procedure
  • Atmospheric temperature and humidity, etc.

Having said that, let me explain the types of welding defects with visual images.

#1) Incomplete penetration

Incomplete penetration in welding

As the name suggests, the incomplete penetration in welding is a defect in which the weld is not completely penetrated throughout the groove.

As shown in the above image, this incomplete penetration generally occurs at the root of the welded joints.


  • Incorrect size of electrode
  • Welding current is low
  • Inaccurate fit-up and groove preparation


  • The correction of this defect is costly as the entire thickness of weld is required to be removed.
  • Re-welding is done in the groove to get the defect free weld, but care must be taken so that the weld groove is wide enough and the electrode can be manipulated correctly in the weld groove.


  • Select the proper electrode
  • Keep welding current high during the first run
  • Proper edge preparation should be done

#2) Lack of fusion

Incomplete fusion in welding

Lack of fusion is the welding defect in which the weld metal is not completely fused with the base metal.


  • Occurs due to the presence of scales, slag and other nonmetallic substances
  • Low welding current
  • Improper deslagging of metal piece
  • Uneven movement of base metal during the welding process


  • Keep the groove surface clean
  • Use recommended welding current
  • De-Slag each metal pieces thoroughly
  • Place the metal pieces correctly near to each other

#3) Undercut

Undercut welding

Undercut is a welding defect which looks like a continuous or discontinuous groove and is located on the base metal.

The undercut welding defect occurs generally on the edge of the weld in the horizontal direction.


  • Very high welding current
  • Wrong electrode angle
  • Side manipulation is more


  • This defect is corrected by filling up the undercut groove with the weld pass

#4) Slag inclusion

Slag inclusion welding

The nonmetallic particles which enter the weld during the welding process is termed as a slag inclusion.


  • This defect occurs in multipass welding due to improper cleaning
  • Weld surfacing contains scale, rust, grit, first, etc.


  • If bare filler rods are used in the welding process, then they should be perfectly cleaned
  • Use proper welding consumables
  • Cleans the salg if multipass welding is to be done
  • Remove scale, grit, slag, from the weld surface before beginning the welding process

#5) Porosity

Porosity in welding defect

The porosity are the spherical cavities that are caused due to the entrapped gases during the solidification of the weld.


  • Faulty composition of present metal
  • Oil, grease, moisture etc present on the weld surface
  • Low welding current
  • Chemically imperfect welding consumables
  • Quick freezing of the weld deposits
  • More moisture in the welding electrode

#6) Crack

welding crack

In welding, the crack is defined as a discontinuity which occurs due to tearing of the metal.

If this tearing occurs in a plastic condition, then it is termed as hot crack and if it occurs in hard state, then it is termed as cold crack.


  • This defect occurs due to excessive heating of parent metal.

Hot cracking

Hot cracking defects occur in welding at a high temperature. 

The size of the hot crack depends upon the stress involved during the solidification process.

Hot cracking can be prevented by preheating the metal to be welded.

Cold cracking

The cold cracking occurs when the weld cools down completely at room temperature.

Cold cracking occurs in the Heat Affected Zone (HAZ) region of the weld.

#7) Spatter

welding spatter

The spatters are the small globules of the metal which are produced from the electrode that scatters over the surface of the weld as well as the surface surrounding the weld.

Spatter generally occurs due to excessive current, frequent interruptions of the arc and due to the arc blow.

#8) Arc blow

The DC arc is better than the AC arc, and so it is widely used in the majority of welding operations.

But the problem with DC arc is that it deflects the arc by means of magnetic field setup due to current flow.

External links:
Visual welding defects image credit: istudiotech

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