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WELDING DEFECTS

What are Welding Defects?

Welding Defects can be defined as the irregularities formed in the given weld metal
due to wrong welding process or incorrect welding patterns, etc. The defect may
differ from the desired weld bead shape, size, and intended quality.

Welding defects may occur either outside or inside the weld metal. Some of the
defects may be allowed if the defects are under permissible limits but other defects
such as cracks are never accepted.

Types of Welding Defects:

Welding defects are broadly classified into two categories, and those are:

External welding defects (Defects occur on the upper surface of the welded work).

Internal welding defects (Defects occur under the surface of the welded work).

External welding defects

• Weld Crack
• Undercut
• Spatter
• Porosity and Blow holes
• Overlap
• Crater

Internal welding defects

• Slag Inclusion
• Incomplete Fusion
• Necklace cracking
• Incompletely filled groove or Incomplete penetration

External Welding Defects

The various types of external defects with their causes and remedies are listed below:

1. Weld Crack

This is the most unwanted defect of all the other welding defects. Welding cracks can
be present at the surface, inside of the weld material or at the heat affected zones.

Crack can also appear at different temperatures:

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Hot Crack – It is more prominent during crystallization of weld joints where the
temperature can rise more than 10,000-degree Celsius.

Cold Crack – This type of crack occurs at the end of the welding process where the
temperature is quite low. Sometimes cold crack is visible several hours after welding
or even after few days.

Causes of Weld Crack:

• Poor ductility of the given base metal.

• The presence of residual stress can cause a crack on the weld metal.
• The rigidity of the joint which makes it difficult to expand or contract the
metals.
• If there is high content on sulfur and carbon then also the cracks may appear.
• Using hydrogen as a shielding gas while welding ferrous materials.

Remedies for Weld crack:

• Using appropriate materials may decrease the chances of crack.

• Preheating the weld and reducing the cooling speed joint helps in reducing
crack.
• Reduce the gap between the weld joints by using reasonable weld joints.
• While welding releases the clamping force slowly which increases fill to
capacity of welding material.

2.Undercut

When the base of metal melts away from the weld zone, then a groove is formed in
the shape of a notch, then this type of defect is known as Undercut. It reduces the
fatigue strength of the joint.

Causes of Undercut:

• If the arc voltage is very high then this defect may

occur.
• If we use the wrong electrode or if the angle of
the electrode is wrong, then also the defect may
form.
• Using a large electrode is also not advisable.
• High electrode speed is also one of the reasons for this defect.

Remedies for Undercut:

• Reduce the arc length or lower the arc voltage.

• Keep the electrode angle from 30 to 45 degree with the standing leg.
• The diameter of the electrode should be small.
• Reduce the travel speed of the electrode.
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3.Spatter

Spatter is the small metal particles that are thrown out of the arc during welding and
get deposited on the base metal around the weld bead along its length.

Causes of Spatter:

• High Welding current can cause this defect.

• The longer the arc the more chances of getting
this defect.
• Incorrect polarity.
• Improper gas shielded may also cause this
defect.

Remedies for Spatter:

• Reducing the arc length and welding current

• Using the right polarity and according to the conditions of the welding.
• Increasing the plate angle and using proper gas shielding.

4.Porosity and Blowholes

Porosity is a group of small voids and blowholes are comparatively bigger isolated
holes or cavities.

They are mainly generated due to entrapped gases.

Causes of Porosity and Blowholes:

• Use of improper electrode and longer arc

• faster arc travel speed.
• Too low and too high arc currents.
• Due to gas entrapment during solidification of the weld.
• Unclean job surface i.e. presence of scales, rust, oil, and grease, etc on the
surface of the job.

Remedies of Porosity and Blowholes:

• Proper selection of electrode and filler materials.

• Improve welding techniques such as preheating of the weld area or an
increase in the rate of heat input.
• Reducing welding speed to allow time for gas to escape.
• Proper cleaning and the prevention of contaminants from entering the weld
zone.
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5.Overlap
When the weld face extends beyond the weld toe, then this defect occurs. In this
condition the weld metal rolls and forms an angle less than 90 degrees.

Causes of Overlap:
• Improper welding technique.
• By using large electrodes this defect may occur.
• High welding current

Remedies for Overlap:

• Using a proper technique for welding.
• Use small electrode.
• Less welding current.

6. Crater

It occurs when the crater is not filled before the arc is broken, which causes the outer
edges to cool faster than the crater. This causes a stress and then crack is formed.

Causes of the crater:

• Incorrect torch angle.

• Use of large electrode:
• Improper welding technique

Remedies for crater:

• Using a proper torch angle may reduce the stress on the metal
• Using a small electrode may also decrease the crater.
• Use a proper technique.

Internal Welding Defects

The various types of internal welding defects with their causes and remedies are
listed below:

1.Slag Inclusion

This is maybe in the form of slag or any other

foreign material, which does not get a chance
to float on the surface of the solidifying weld
metal and thus gets entrapped inside the
same.
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If there is any slag in the weld, then it affects the toughness and metal weldability of
the given material. This decreases the structural performance of the weld material.
Slag is formed on the surface of the weld or between the welding turns.

Causes of Slag:

• Slag is formed if the welding current density is very small, as it does not
provide the required amount of heat for melting the metal surface.
• If the welding speed is too fast then also slag may occur.
• If the edge of the weld surface is not cleaned properly then also slag may form.
• Improper welding angle and travel rate of welding rod.

Remedies for Slag Inclusion:

• Increase the current density

• Adjust the welding speed so that the slag and weld pool do not mix with each
other.
• Clean the weld edges and remove the slags of previous weld layers
• Have a proper electrode angle and travel rate.

2. Incomplete Fusion

Incomplete fusion occurs when the welder does not accurately weld the material and
the metal pre solidifies which leads to a gap which is not filled with the molten metal.

Causes of Incomplete fusion:

• It occurs because of the low heat input.

• When the weld pool is very large and runs ahead
of the arc.
• When the angle of the joint is too low.
• Incorrect electrode and torch angle may also lead
to incomplete fusion.
• Unproper bead position.

Remedies for Incomplete Fusion:

• Increasing the welding current and decreasing the travel speed helps in
removing the chances of incomplete fusion.
• Reducing the deposition rate.
• Increasing the joint angle.
• Try to position the electrode and torch angle properly so that the edges of the
plate melt away.
• Positioning the bead properly so that the sharp edges with other beads can be
avoided.
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3. Necklace Cracking

It occurs in the use of electron beam welding where the weld does not penetrate
properly. Therefore, the molten metal does not flow into the cavity and results in a
cracking known as “Necklace Cracking”.

Causes of Necklace Cracking:

• Improper welding technique.

• It occurs in materials such as nickel base alloys, stainless steel, carbon steels
and Tin alloys.
• Using high speed of electron beam welding

Remedies for Necklace Cracking:

• Using a proper welding technique reduce the chances of necklace cracking.

• Using proper materials for welding.
• Using a constant speed during the welding process.
• Improper welding technique

4.Incomplete filled groove or Incomplete Penetration:

Incomplete penetration occurs when the Depth of the welded joint is insufficient.

Penetration is defined as the distance from the base plate top surface to the
maximum extent of the weld nugget.

Causes of Incomplete penetration:

• Improper joints.
• Too large root face, root gape, and bevel gear.
• Wrong hold position of the electrode.
• Too large electrode diameter and longer arc length.
• Less arc current and faster arc travel speed.
• Incorrect polarity while welding with DC.

Remedies of Incomplete penetration:

• Increasing the heat input.

• Reducing travel speed during welding.
• Ensuring that the surface to be joint fit properly.
• Changing the joint design.

Hot Tear Welding defects:

In this welding defect, the deposited metal being hot starts developing crack from
the nearby edge so that after it has been solidified the crack increases.
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The hot tear is also known as solidification cracking, due to tearing of the grain
boundaries of weld metal before complete solidification has taken place and metal is
still in the plastic state.

Causes of Hot tear:

• Improper selection of proper materials.

• Welding current is not proper.
• Improper electrode thickness.

Remedies of Hot tear:

• Select the proper electrode material.

• Welding current should be optimum as per the requirement.
• Electrode thickness should be optimum and according to the base metal to be
welded.