Understanding and preventing common welding defects

Sveise-ABC

Understanding and preventing common welding defects

15. februar 2024

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.

Susanna Norja

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.

POSSIBLE CAUSES

HOW TO AVOID?

Too narrow joint preparation

Ensure that the joint preparation is sufficiently wide

Incorrect torch/electrode angle

Make 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 flooding

Impurities on the joint faces

Clean the joint faces

’Downhill welding’

Use vertical up welding

Too long arc/too high voltage

Use shorter arc/less voltage

Too low heat input

Increase heat input

Porosity

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.

POSSIBLE CAUSES POSSIBLE CAUSES

HOW TO AVOID?

Poor gas shielding

Seal any air leaks, reduce any excessively high gas flow rates, avoid weld pool turbulence and drafts

A wet electrode

Dry the electrode

Impurities on the joint faces, such as rust, primer

Clean the joint faces

Too long arc/high voltage

Decrease voltage

Too low heat input

Use 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.

POSSIBLE CAUSES

HOW TO AVOID?

Poor joint design or preparation

Expand the root opening or decrease the size of the root face

Excessively long arc length

Weld with a shorter arc / reduce the voltage

Too large an electrode diameter

Use a smaller electrode

Excessively high welding speed

Decrease the welding speed

Too small heat input

Increase heat input

Undercutting

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.

POSSIBLE CAUSES

HOW TO AVOID?

Too long arc/voltage

Reduce the voltage

Incorrect angle of the electrode

Use appropriate electrode angles

Excessive weaving of the electrode

Perform the weaving motion properly, by pausing at each side of the weld bead

Excessively high current

Reduce the current

Too large throat thickness

Use 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.

POSSIBLE CAUSES

HOW TO AVOID?

Incorrect stopping technique

Stop 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.

POSSIBLE CAUSES

HOW TO AVOID?

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 removal

Remove all slag between runs

Too low heat input

Increase the heat input

Slag flooding ahead of the arc

Aim the arc toward the weld pool

Too narrow joint

Increase 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.

POSSIBLE CAUSES

HOW TO AVOID?

Too high heat input to the joint

Reduce the heat input

Too large air gap

Use a smaller air gap

Too small a root face

Enlarge the root face

Spatter

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.

POSSIBLE CAUSES

HOW TO AVOID?

Inappropriate welding parameters

Adjust the welding parameters

Too long an arc / excessively high voltage

Weld with a shorter arc / reduce the voltage

Wet, uncleaned, or damaged electrodes

Use 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 blow

Change the position of the earth return clamp / weld toward the clamp / bend the stick/torch in the direction of the blow

Incorrect polarity

Change 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.

POSSIBLE CAUSES

HOW TO AVOID?

Poor component fit-up before welding

Perform the joint fit-up work accurately

Deformations during welding

Rigidly fix parts to be welded in place, and use the correct welding sequence

Breaking of tacks during welding

Perform the tack welding properly

Uncorrect tolerance of the welding components

Check 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.

POSSIBLE CAUSES

HOW TO AVOID?

Incorrect torch/electrode angle

Use the correct torch/electrode angles

Too large a weld pool

Reduce the deposition rate

Magnetic arc blow

Move 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.

POSSIBLE CAUSES

HOW TO AVOID?

Too much filler metal for the welding speed used

Increase the welding speed or reduce the amount of filler metal

Too large an electrode diameter

Use a smaller diameter electrode, or increase the joint angle

Too small or unbeveled groove

Use beveled groove

Too low heat input

Use 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.

POSSIBLE CAUSES

HOW TO AVOID?

Too low a width-to-depth ratio for the weld

Ensure 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 expansion

Minimize the degree of restraint by using appropriate edge preparation and accurate joint fit-up

High carbon content in the weld

Use a low carbon content filler material

Wrong filler metal

Use right filler metal

Segregation of impurities to the center of the weld

Choose a base material with less impurities

Susanna Norja
Author

Susanna Norja

Editor-in-chief of the Welding Value blog, content producer and Social Media Manager at Kemppi until March 2024.

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