13 Common Welding Defects you need to avoid

This article will shed light on the various types of welding defects, why they occur, and how to prevent them.

During the welding process, welders may experience some defects.

Welding defects can weaken the joint and, in severe cases, may ruin the workpiece.

So to avoid this from happening, you need to grasp a good understanding of the various defects. 



Slag Inclusions 

Lack of Fusion 

Incomplete Penetration 




Excess Reinforcement or Penetration 

Burn Through 



Mechanical Damage 

1. Porosity

It causes pores on the surface or within the bead, damaging the workpiece.

A welding defect occurs due to the accumulation of gas bubbles inside the welded zone.

What causes it?

Porosity happens due to:

  • The presence of moisture, grease, oil, or surface contamination.
  • The use of a longer arc
  • The use of high gas flow
  • Insufficient or excessive shielding gas. Or when the electrode is not well coated.

How to prevent it?

To avoid the occurrence of this defect, all you have to do is:

  • Cleaning the surface well before starting the welding process
  • Avoid the use of a long arc.
  • Set the shielding gas flow correctly
  • Choosing suitable electrode and filler materials

2. Cracks

Welding cracks refer to a depression left at the termination of a weld where the weld pool is left unfilled.

Cracks are one of the most severe and apparent defects in the weld. They can grow fast, worsening the problem and may cause the failure of the welded structure.

There are three main types of cracks: cold, hot, and crater.

Hot cracks occur when using the wrong alloy filler material. 

Deformities in the base metal often cause cold cracks. 

Crater cracks occur at the end of the welding process before the welder completes the welding joint.

What causes them?

Cracks occur when:

  • Applying low current with high welding speed
  • The base metal is not clean.
  • The metal contains a high mixture of sulfur and carbon.
  • Using hydrogen while welding ferrous metals
  • Using inadequate preheating
  • Rapid cooling of the weld joint
  • Residual stress solidification due to shrinkage
  • The design concept is poor.

How to prevent them?

To prevent cracks from happening, all that you have to do is:

  • Use suitable materials
  • Clean the metal surface before starting the welding process
  • Avoid rapid cooling of the weld area.
  • Preheat the metal to the required level before starting welding
  • Use the correct joint design.
  • Use a good mixture of sulfur and carbon in the metal.
  • Ensure that the crater is adequately filled to prevent crater cracks.
  • Utilize the appropriate welding speed and current.

3. Slag Inclusions

Slag inclusions occur when impurities are trapped inside a weld, decreasing the joint’s strength and weakening it.

This (i.e., the impurities trapping) happens when the flux, a solid shielding material applied when welding, melts on the surface of the weld region.

What causes them?

Slag inclusions occur due to:

  • The use of low welding current
  • Gaps and asymmetries in the joint
  • Improper metal cleaning
  • Fast welding speed
  • Incorrect electrode angle
  • Poor electrode selection
  • Wrong electrode manipulation

How to prevent them?

To avoid this problem, you can follow these steps:

  • Reduce The speed of welding 
  • Clean the material before starting the welding process
  • Decrease the rapid cooling 
  • Increase the current density
  • Ensure good joint fit-up and correct any asymmetries
  • Adjust the angle of the electrode

4. Lack Of Fusion

Incomplete fusion happens when there is a lack of suitable fusion between the metal and weld. It produces a gap inside the joint that is not filled with molten metal.

Due to the gaps and voids resulting from the lack of fusion, the joint will be structurally impaired.

What causes it?

Lack of fusion can result from:

  • Low heat input
  • The contamination of metal surface
  • Too fast travel speed.
  • Wrong electrode angle
  • Using the wrong electrode diameter compared to the thickness of the material

How to prevent it?

You can avoid the lack of fusion by:

  • Using the proper heat input
  • Cleaning the welding area properly
  • Decreasing the travel speed to minimize the chances of incomplete fusion
  • Ensuring that the electrode angle is suitable for welding
  • Using the correct diameter of the electrode to fit the thickness of the workpiece

5. Incomplete Penetration

Incomplete penetration occurs when the metal groove is not filled perfectly. 

Thus, the weld metal does not fully spread through the joint thickness.

What causes it?

Poor penetration results from:

  • Moving the bead too fast does not allow enough metal to accumulate in the joint
  • Using a low amperage setting may not be enough to melt the metal completely.
  • Incorrect position of the electrode
  • The use of larger diameter electrode
  • The use of improper joints
  • Too much space between the welded metal

How to prevent it?

To prevent poor penetration, you can follow these steps:

  • Use correct joint geometry and ensure proper alignment
  • Select an appropriate amperage of welding
  • Improve the design of the joint
  • Adjust the position of the electrode and make sure it is very accurate
  • Use right diameter electrodes as suitable for your welding.
  • Decrease the arc travel speed

6. Spatter 

It occurs when metal particles from the weld are stuck near the weld area. Once they cooled, they became tough to remove.

Spatter is very common in the gas-metal arc welding type.

What causes it?

Spatter can emerge because of:

  • The contamination of the weld surface
  • Improper gas shielding
  • Utilizing too high amperage current and too low voltage settings
  • Using incorrect polarity
  • Positioning the electrode at a very steep angle
  • Using the larger arc and wet electrode

How to prevent it?

Although eliminating all spatter is quite impossible, there are still a few steps you can do to reduce it.

  • Adjust the amperage settings
  • Use the proper arc and electrode according to the welding.
  • Clean the metal surface before starting the welding process
  • Decrease the arc length and increase the electrode angle
  • Use proper gas shielding.
  • Use correct polarity

7. Undercut

Undercuts can be defined as many grooves that emerge in the base metal near the weld toe or root of the weld.

Those mentioned above can introduce weak points that reduce the strength of the weld and workpiece and lead to some cracks.

What causes it?

Among the causes of Undercut, we can mention the following:

  • Improper electrode angle
  • improper selection of a gas shield and filler metal
  • The use of high welding current
  • The contamination of the base metal 
  • Too fast weld speed
  • Using larger diameter electrodes

How to prevent it?

We can avoid this welding defect by following these steps:

  • Decrease the arc length and use a suitable electrode angle
  • Ensure the cleanliness of the surface
  • Select the shielding gas with the proper structure
  • Ensure that the gas flow meter is configured with the correct flow settings
  • Decrease the travel speed of the electrode

8. Overlap

It occurs when the molten metal does not fuse with the base metal resulting in an overlap.

This overlap may extend to form an angle not exceeding 90 degrees.

When this happens, it means that the metal is not fused well.

What causes it?

Many factors lead to the occurrence of this defect, which we can mention:

  • Using large-size electrodes in welding
  • Using too much electric current
  • Wrong electrode angle
  • Applying improper welding technology
  • Wrong torch angle

How to prevent it?

There are some remedies for overlaps, such as:

  • Employ the proper welding technique to avoid the wrong arc length
  • Be sure not to use large-size electrodes.
  • Keep the correct torch angle.
  • Use low welding current.

9. Excess Reinforcement or Penetration

It happens when there is too much filler material in the welding joint. Thus the weld becomes too big or has too much convexity.

What causes it?

It occurs due to:

  • The use of improper levels of current or heat 
  • big gap between the welding pieces
  • Uneven travel speed on the feed wire
  • Too low voltage

How to prevent it?

You can avoid excess reinforcement from happening by:

  • Keeping the torch moving at a proper speed
  • Adjusting your voltage and make sure it is not too low
  • Setting the current correctly and avoiding excess heat.
  • Aligning the pieces well so that the gap is not too large

10. Burn Through

Burn through is the result of using a high degree of heat. This will generate holes that destroy the joint.

What causes it?

There are many reasons for burn-throughs, such as:

  • The use of excessive heat input into the weld joint
  • Slow travel speed
  • Poor joint preparation
  • The contamination of base metal
  • Incorrect arc length

How to prevent it?

Here are some tips to avoid the occurrence of this defect:

  • Clean the base metal before welding
  • Maintain a moderate arc length
  • Use a lower current level.
  • Complete passes quickly
  • Use a shallow travel angle.
  • Verify machine settings before welding
  • Avoid excessive gaps between the pieces.

11. Whiskers 

Whiskers happen when short lengths of electrode wire stick through the weld on the root side of the joint.

This undesirable result occurs when the welding wire is pushed ahead of the weld pool.

What causes them?

The reasons behind the occurrence of whiskers are:

  • Excessive travel speed
  • Increase in the electrode wire feed speed

How to prevent them?

You can prevent this from happening by:

  • reducing the electrode wire feed speed
  • Reducing the wire-feed speed

12. Underfill 

Underfill emerges when there is not enough filler metal welded into the groove. 

It makes the total thickness of the weld less than the entire thickness of the base material next to the weld.

What causes it?

The leading causes of Under-fill defects are:

  • High welding travel speed
  • High heat inputs
  • Improper size electrode/filler wire

How to prevent it?

You can prevent Underfill from happening by:

  • Using correct current and heat input
  • Utilizing the right size electrode/filler wire
  • Avoid using high travel speeds.

13. Mechanical damage

It is an indentation in the workpiece’s surface caused by poor techniques during the welding process.

What causes it?

Mechanical damage can occur because of:

  • an extra force applied during chipping
  • incorrect handling of the electrode holder
  • Incorrect use of a grinder

How to prevent it?

To avoid facing mechanical damage during welding, try to:

  • Avoid heavy hammer blows
  • handling the holder and the welding electrode carefully
  • Don’t let pieces of metal impact or fall over your welds.


While welding, the defects can show at any moment and seem impossible to avoid. 

So, if you want to prevent them from happening, you should learn more about welding fundamentals, adopt good welding techniques, and practice as much as you can.

Picture of Jeremiah Lambert

Jeremiah Lambert

A certified welder with almost a decade of experience in MIG, Flux, Arc, TIG welding, and metal forgery. Welding certificate course graduate with excellence. Also familiar with and enthusiastic about real estate and home improvement.
Arc Welding

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