Understanding and preventing common welding defects

Understanding and preventing common welding defects

Welding demands precision, but even skilled welders can encounter defects. Understanding common welding issues is critical to ensure high-quality results. Here are some frequent welding defects and how to avoid them.

Lack of fusion

When two pieces of metal are welded together, they should melt and bond at the interface to create a strong joint. If the weld metal doesn’t fully fuse with either the base metal or the previous weld layer, it can result in weak and unreliable joints. This is known as lack of fusion, and it occurs when there is insufficient melting and bonding. To avoid this problem, it’s essential to properly prepare the joint and use the correct welding technique and parameters.

Too narrow joint preparationEnsure that the joint preparation is sufficiently wide
Incorrect torch/electrode angleMake sure the torch/electrode angle will produce
adequate side-wall fusion
Excessively high current or too low a
welding speed, which creates a weld
pool flooding ahead of the arc,
resulting in insufficient penetration
Select welding parameters (high welding current,
short arc length, and not too high a welding speed)
that promote sufficient penetration without causing
Impurities on the joint facesClean the joint faces
’Downhill welding’Use vertical up welding
Too long arc/too high voltageUse shorter arc/less voltage
Too low heat inputIncrease heat input


Welding porosity refers to forming small air pockets or pores that weaken the weld. These pores occur when undesired gases get trapped within the molten weld puddle. To avoid porosity, it is crucial to maintain good gas shielding, ensure proper cleaning of the joint faces, and use correct welding parameters.

Poor gas shielding Seal any air leaks, reduce any excessively high gas flow rates,
avoid weld pool turbulence and drafts
A wet electrodeDry the electrode
Impurities on the joint faces, such as rust, primerClean the joint faces
Too long arc/high voltageDecrease voltage
Too low heat inputUse higher heat input

Lack of penetration

Lack of penetration in welding is a term used to describe a defect where the weld metal does not fully extend the joint thickness. This defect can weaken the joint and increase the risk of potential failure. To avoid this, it is important to adjust welding parameters and techniques to ensure complete weld penetration into the base metal.

Poor joint design or preparationExpand the root opening or decrease the size
of the root face
Excessively long arc lengthWeld with a shorter arc / reduce the voltage
Too large an electrode diameterUse a smaller electrode
Excessively high welding speedDecrease the welding speed
Too small heat inputIncrease heat input


Undercutting in welding is a defect that happens when a groove or depression runs along the toe of the weld. This occurs when the filler metal fails to properly fill the melted base material. As a result, the base of the weld joint has a concave shape. Unfortunately, this flaw reduces the welded joint’s structural integrity, making it more prone to cracks and failures.

Too long arc/voltageReduce the voltage
Incorrect angle of the electrodeUse appropriate electrode angles
Excessive weaving of the electrodePerform the weaving motion properly, by pausing
at each side of the weld bead
Excessively high currentReduce the current
Too large throat thicknessUse multipass welding

Crater cracks and crater pipes

Crater cracks occur when the weld pool cools down too quickly. These cracks make the weld weaker and more prone to failure. They usually spread outwards from the end of the weld crater. Crater pipes, on the other hand, are defects that appear at the end of a weld when the welding arc stops. They can be shallow depressions or elongated pores. Crater pipes form due to techniques like suddenly stopping the wire feed or using autogenous methods (such as TIG welding). Proper welding techniques and parameters, along with adding filler material at the end of the weld, can help prevent these types of cracks.

Incorrect stopping techniqueStop welding by moving the arc backward
a little or to the groove side
Rapid solidification of a large weld pool when
the welding current is switched off
Progressively reduce the welding current,
to decrease the weld pool size

Slag inclusions

Slag inclusions are a frequent type of welding defect that arises when slag, a by-product of welding, gets stuck inside the weldment. This can cause a range of performance problems in the long run. To avoid this problem, cleaning thoroughly and using the appropriate welding technique is crucial.

Voids caused by inadequate overlap
of two adjacent weld beads
Use the correct electrode size and angle, and use
welding techniques that produce smooth weld beads
Insufficient slag removalRemove all slag between runs
Too low heat inputIncrease the heat input
Slag flooding ahead of the arcAim the arc toward the weld pool
Too narrow jointIncrease the joint angle

Excessive penetration

Excessive penetration in welding refers to a situation when weld metal penetrates deeper into the base metal than intended. To manage the level of penetration, controlling the heat input and speed of welding is crucial. This phenomenon is particularly important in pipe welding, as it can impact fluid flow and cause erosion and corrosion issues.

Too high heat input to the jointReduce the heat input
Too large air gapUse a smaller air gap
Too small a root faceEnlarge the root face


During the welding process, small droplets of molten metal can scatter from the weld pool and stick to various surfaces. This is called spatter, and it can negatively affect both the appearance and quality of the weld. The primary cause of spatter is an unstable welding arc. To reduce spatter, it’s important to fine-tune the welding parameters and potentially adjust the gas flow or mixture. By effectively managing spatter, you can ensure that your welds are of high quality and visually appealing.

Inappropriate welding parametersAdjust the welding parameters
Too long an arc / excessively high voltageWeld with a shorter arc / reduce the voltage
Wet, uncleaned, or damaged electrodesUse dry and undamaged electrodes
Impurities on the fusion faces or in the filler
materials – e.g., rust
Grind the fusion faces, and use clean filler materials
Magnetic arc blowChange the position of the earth return clamp /
weld toward the clamp / bend the stick/torch in the
direction of the blow
Incorrect polarityChange the polarity

Linear misalignments (Mismatch)

Linear misalignment in welding is a defect that occurs when the edges of the weld joint are not aligned correctly in a straight line. This results in a deviation or offset along the length of the weld bead. To minimize this defect, it is important to use proper fixturing and alignment techniques and adhere to welding procedures.

Poor component fit-up before weldingPerform the joint fit-up work accurately
Deformations during weldingRigidly fix parts to be welded in place, and use the
correct welding sequence
Breaking of tacks during weldingPerform the tack welding properly
Uncorrect tolerance of the welding componentsCheck tolerances

Excessive fillet weld asymmetry

Excessive fillet weld asymmetry in welding occurs when the two legs of a fillet weld are not of equal length, leading to an uneven distribution of weld material. This imbalance can affect the structural integrity and strength of the welded joint. This asymmetry can compromise the weld’s ability to withstand loads and stresses as intended, potentially leading to premature failure or deformation under operational conditions.

Furthermore, excessive fillet weld asymmetry refers to a condition where the fillet weld’s shape deviates significantly from the desired idealized design. Fillet welds are commonly used to join two components at an angle of 90 degrees and are characterized by their triangular cross-section.

Incorrect torch/electrode angleUse the correct torch/electrode angles
Too large a weld poolReduce the deposition rate
Magnetic arc blowMove the earth return clamp, use the shortest arc
possible, reduce the welding current, angle the torch/
electrode opposite the direction of arc blow, and/or
use an AC power source

Excess weld metal (weld reinforcement)

Excess weld metal, also known as weld reinforcement, occurs when the volume of weld metal deposited in the joint exceeds what is necessary for the intended strength and contour of the weld. While some reinforcement is typically required to compensate for weld shrinkage and ensure the weld is strong enough, excessive weld metal goes beyond this, leading to a build-up that can affect the aesthetic and functional aspects of the weld. This surplus can lead to increased stress concentrations, unnecessary weight, and material wastage, as well as potential difficulties in meeting dimensional tolerances and can affect the performance in service by altering the stress distribution within the welded component. Managing the amount of weld metal is crucial for achieving an efficient, cost-effective, and structurally sound weld that meets the specified design and quality standards.

Too much filler metal for the welding speed usedIncrease the welding speed or
reduce the amount of filler metal
Too large an electrode diameterUse a smaller diameter electrode,
or increase the joint angle
Too small or unbeveled grooveUse beveled groove
Too low heat inputUse higher heat input

Cracks (e.g. hot cracking)

Cracks in welding, such as hot cracking, are one of the most severe defects that can occur during the welding process. These cracks occur when localized stresses exceed the ultimate tensile strength of the base metal. Stresses develop as the weld cools and solidifies. This type of cracking can be caused by many factors, including improper filler material selection, high levels of impurities in the base metal, excessive heat input, and rapid cooling rates. It is essential to understand the mechanisms behind hot cracking and follow proper welding practices to prevent this detrimental defect, which ensures the integrity and longevity of welded structures.

Too low a width-to-depth ratio for the weldEnsure that the width-to-depth ratio of the weld is
above 1 with non-alloy steels / above 1.5 with
stainless steels
High stresses due to the large amount of thermal
Minimize the degree of restraint by using appropriate
edge preparation and accurate joint fit-up
High carbon content in the weldUse a low carbon content filler material
Wrong filler metalUse right filler metal
Segregation of impurities to the center of the weldChoose a base material with less impurities
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