Welders Galore

Welders Galore

Common Types of Welding Defects and How to Prevent Them

Common types of defects in welding can occur due to using substandard materials, wrong welding techniques, or not preparing the work-piece sufficiently. However, regardless of the cause, welding defects can lead to severe consequences and the weld failing.

 Incomplete fusion causes a potential defect in welding

The only way to avoid weld defects is to know what causes them. Then, armed with this knowledge, you can take proactive steps in the welding process to ensure the weld joint is solid. This way, you can avoid spatter, incomplete fusion, any types of cracks, slag inclusion, and other common welding defects.

When you take steps to prevent welding defects, you can admire the weld surface and weld bead, knowing that the joint is solid, strong, and will withstand stresses and strains. 

This article explores the causes of common weld defects and how to prevent them. In addition, you will learn how to avoid improper welding techniques that result in external and internal defects.  

What Is A Weld Defect?

Weld defects are imperfections, flaws, and irregularities that affect the integrity of a weldment. For example, the defect could be on surfaces like a spatter, messy weld beads, or discoloration. Or the internal defect could be incomplete penetration, incomplete fusion, air bubbles, or internal cracks not noticeable on a visual inspection.

Weld defects are classified according to ISO 6520, “Classification of geometric imperfections in metallic materials.” Additionally, limits of weld defects are specified in ISO 5817 and ISO 10042. The weld appearance or structure is classified as defective if these limits are exceeded.

Therefore, a weld defect can be one of two things:

·        Appearance of the weld is not aesthetically pleasing.

·        There is an unacceptable weakness in the weld joint.

Types of Welding Defects

Welding defects are an unfortunate part of any welding job. And they can occur for a variety of reasons. Defects can cause problems such as weaker welds, cracks, and other structural issues. Knowing how to identify these welding defects is the key to preventing them in the future.

All types of welding defects are classified as external defects or internal defects.

External Welding Defects

External weld defects show up on the surface of the weld joint. These cracks, overlaps, ugly beads, and spatter defects are usually easily detectable during a visual inspection. However, Dye Liquid Penetrants (DPI) or Magnetic Particle Inspection (MPI) can detect smaller, less noticeable weld imperfections. 

Internal Welding Defects

Internal welding defects are a common issue for welders. Defects like incomplete penetration, blowholes, slag inclusions, and incomplete fusion are usually not visible on the weld’s surface. Non-destructive testing methods to spot common internal welding defects include Radiographic Testing (RT) or Ultrasonic Testing (UT).  

Nine Common Types Of Weld Defects

1/ Undercut welding defect

Undercut is a common welding defect when the weld has melted away from the base metal. This creates indentations or grooves along the welding joint. Undercuts typically occur due to a fast weld speed, poor welding techniques, incorrect filler, or a high current.

The result of undercuts in welds is reduced strength, and the joint can become more susceptible to fatigue.

How to prevent undercutting defects during welding

The best way to remedy undercuts in welding is to use the proper techniques for the material. This includes using the right speed and pass technique and ensuring the electrode is at the correct angle. It’s also crucial to ensure the proper shielding gas mixture. Also, if undercuts are common, try reducing the welding arc length.

2/ Over-roll or overlap welding defect

One of the most common welding defects is over-roll or overlap. This issue occurs when the filler material at the weld’s toe fails to bond with the base metal. As a result, the weld pool flows excessively, and the lack of fusion causes a weak spot in the weld join.

Like many common welding defects, incorrect welding patterns are typically to blame. For example, the most common cause of overlap is using a varying electrode angle, high welding current, or electrodes that are too large. 

How to prevent overlap welding defects

Suppose you notice overlapping on your welds. In that case, the simplest solution is to use the correct electrode size and keep a uniform angle when welding.

3/ Incomplete fusion causes a potential defect in welding

A lack of fusion is a type of welding defect when inaccurate welding prevents the filler material from bonding to the base metal. The resulting gaps in the joint significantly weaken the weldment and cause structural weaknesses.

What typically causes incorrect fusion during the welding process? Here are a few reasons:

·        Failure to clean the surface before welding

·        Wrong electrode size or incorrect angle

·        Fast welding speed

·        Low heat input

·        The pool of molten metal is large and travels faster than the arc

How to prevent a lack of fusion when arc welding

The first step to ensure proper fusion is thoroughly cleaning the metal surface. Then use the correct heat input, electrode, and travel speed. Also, it’s vital to control the size of the molten weld pool.

4/ Poor penetration weakens weld joints

Incomplete penetration is one of the main types of welding defects. Lack of penetration occurs when the weld bead fails to fill a metal groove or joint to the bottom, resulting in a weakened joint. Poor penetration can happen for several reasons, such as using too much heat, welding too quickly, or using the incorrect welding current.

Good preparation is always vital when welding metal, and correctly aligning the joint will help ensure good penetration. 

How to get good penetration in a welding job

To avoid weld defects caused by incomplete penetration, use the correct arc travel speed and position the electrodes properly. However, suppose you already do that, and penetration defects continue. In that case, you may need to improve the joint design and align the metal parts properly before welding to create strong joints with good penetration and strength.

5/ Cracks — External weld defect

Surface cracks are one of the most common and serious welding defects. Cracks in welds usually cause the workpiece to be rejected because it is severely weakened. There are three types of cracks common in welding:

·        Cold cracks: Cold cracking appears when the metal has cooled. Solidification cracking can happen hours or even days after welding. Typically, this type of crack travels parallel to the fusion boundary. They are usually caused by insufficient preheating, low temperature, or poor base materials or fillers. 

·        Hot cracks: High temperatures and impurities in the metal can cause hot cracks to appear. They can either be liquidation cracks or solidification cracks.  

·        Crater cracks: These weld defects occur as the parent metals and the bead cool and shrink. Insufficient volume in the join will cause crater cracks.

Weld crack shapes and sizes can be described as the following: 

·        Longitudinal cracks

·        Center-line cracks

·        Root cracks

·        Star cracks

·        Transverse cracks

·        Branching cracks

How to prevent cracks in welded joints

Two things can help prevent cracking when welding. First, ensure to clean the weld metal thoroughly before applying the arc. Second, preheat the metal before welding. Additionally, using the correct welding techniques like speed, current, and shielding gas mixture will prevent cracking.

6/ Porosity in welding is a serious defect

Types of Welding Defects

Also known as wormhole welds or blowholes, porosity is an internal or external effect caused by gasses trapped in the bead. For example, small air bubbles form when gasses like carbon dioxide, hydrogen, and steam contaminate the bead. The porous appearance can sometimes be visible on the surface. Or a cross-section of the weld bead could look like a sponge.

Porosity weakens the joint, making it susceptible to fatigue and stress. 

How to prevent porosity in welding

To prevent blowholes and porosity in welds, ensure base materials and electrodes are free from contamination. Additionally, you should use the right amount of shielding gas and proper speed to prevent gas bubbles from forming in the bead. 

7/ Slag inclusions are dangerous weld defects

Slag inclusion is a common welding defect during stick welding or flux-cored arc welding processes. Using flux—a solid shielding material—can result in impurities getting trapped in the weld. Apart from making the weld look dirty, slag or flux inclusions in a weld impacts its strength, making it weaker and susceptible to breaking.

How to prevent slag inclusion defects in your welds

When stick welding, shielded metal arc welding, or flux-core arc welding, it is crucial to clean the weld bead before depositing the next layer. Also, reducing welding speed and avoiding rapid cooling can help prevent excess flux from contaminating the weld. 

Other ways to remedy slag inclusion are the following:

·        Adjust the electrode’s angle

·        Allow sufficient space for the molten weld metal puddle to form

·        Clean metal before welding

8/ Burn Through

Burn-through is a welding defect when excessive heat is applied during the welding process. This defect appears as holes blown in the center of the bead. The result is a weld that is completely useless. Burn-through defects are typically common in thin stock material less than 1/4 inch thick.

However, if the welder settings are too high or there’s a large gap between the pieces being welded, you may end up with unwanted burn-through defects in the weld. 

How to prevent burn through

The best way to avoid blow holes in welding is to use the correct welder settings for the stock thickness. Additionally, it’s vital to use the correct speed of travel and ensure gaps between metal pieces are not too large.

9/ Spatter on Weld Material

Welding spatter is an annoying aesthetic defect when the welding arc ejects small metal particles. These appear as spots or bumps along the length of the bead. Although it’s not a structural defect, the spatter on a weld looks sloppy and unprofessional. This welding defect is common in gas-metal arc welding.

Although the weld surrounded by spatter may be structurally sound, it can still cause damage. For example, spatter projections can be sharp and cause injury when handling the piece. 

How to remedy spatter when welding

Spatter on Welding Material

Here are a few simple ways to prevent spatter from ruining the appearance of your welds:

·        Ensure the metal surfaces are clean before starting

·        Use the correct polarity, keep the arc short, and increase the electrode angle

·        The right type of shielding gas should be used

·        Increase the current density

·        Use the correct voltage and amperage for the work-piece

Common Types of Welding Defects — In Conclusion

Using proper welding techniques is key to avoiding welding defects. Sometimes, it takes trial and error to get a perfect weld. This may involve using the correct amperage, current density, electrode angle, and travel speed to create an aesthetically pleasing, strong weld that withstands stress. In addition, always cleaning base metals and preheating the surface can help prevent many common welding defects among beginners.

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