welding defects

Different Types of Welding Defects

Welding defects are irregularities or imperfections formed in a weld due to wrong welding techniques, patterns, or processes. These defects cause variations in the size, quality, and bead shape of workpieces. 

Welding defects can occur at the weld’s exterior or interior surface. Some defects formed are insignificant because they are below the permissible limits, but other ones, such as cracks, for instance, cannot be accepted. The most common types of welding defects include; slag inclusion, porosity, incomplete fusion, flux inclusion, undercutting, cracks, and incomplete penetration. However, there are remedies for these, so the weld can maintain good quality. 

This article analyses the common types of welding defects, their classes, types, causes, and the best remedies to eliminate them. 

Welding defects are typically classified into two; external and internal. 

For External Defects: 

  • Porosity 
  • Crater 
  • Crack 
  • Spatter 
  • Undercut 
  • Overlap 

While for the Internal Welding Defects: 

  • Incomplete fusion 
  • Incomplete penetration 
  • Necklace cracking 
  • Slag inclusion 


A situation where bubbles of gas are within the welded area is termed ‘Porosity‘. 

Causes of Porosity

  • An improperly coated electrode. 
  • A very long arc is also one of the probable causes. 
  • High current. 
  • Oil on the surface of the weld. 


  • Smaller arcs. 
  • Gently carry out the process to allow the escape of gas. 
  • Use the proper technique. 
  • Clean off oil from the welding surface. 
  • Select the proper electrode. 
  • Reduce the current. 


When the crater isn’t filled up before the arc breaks, it makes the outer edges cool faster. As a result, this stresses the material and leads to the crater defect. 


  • Incorrect angle of the torch. 
  • Wrong welding technique. 
  • Large size electrodes. 


  • Use smaller electrodes. 
  • Implement the correct technique. 
  • Get the suitable torch angle to reduce the stresses on the workpiece. 


Cracks are the most unacceptable defect amongst all other defects. You can find cracks in the interior, surface, and heated areas of the material. This defect can also be formed at various temperature degrees. On weld cracks, they are separated into hot and cold cracks.

Hot cracks are prevalent during the crystallization of joints which requires high-temperature weld. During the crystallization process, the temperature can exceed 10,000°C 

On the contrary, cold cracks are caused due to low temperatures at the end of the process. In some cases, these cracks are visible after hours of weld completion. Sometimes it takes few days. 


  • Cracks appear when there is a large amount of carbon and sulfur content. 
  • A rigid weld joint impedes contraction and expansion of the workpiece. 
  • Applying hydrogen as a shield while welding ferrous metals. 
  • Residual stress on the weld material. 
  • A base metal of low ductility. 


  • The welder should use the correct type of weld joint for the material. 
  • Weld preheating and reduction of cooling joint speed can go a long way in reducing cracks. 
  • Using the suitable material. 


One of the significant spatter symptoms is when there are metal drops from the welded area and then it gets stuck to the material’s surface. 

Spatter Causes

  • Wrong polarity. 
  • Use of inappropriate shielding gas. 
  • The higher the arc length, the more the material gets prone to spatter. 
  • High wielding voltage.


  • Use the appropriate shielding gas. 
  • Adjust plate angle. 
  • The voltage and arc length should be reduced. 
  • Always use the correct polarity, and this is based on the conditions of the weld. 


This welding defect occurs when the base material melt from the welded area, forming a groove that looks like a notch. Due to undercut, the joint’s fatigue strength is lowered. 

Undercut Causes

  • If the welder uses the wrong electrode angle or electrode itself, then there must be an undercut. 
  • Welding with an oversize electrode. 
  • Fast rate of electrode speed. 
  • High ARC voltage. 


  • Lower the arc voltage or length. 
  • If the electrode’s travel speed is too high, reduce the rate. 
  • Use an electrode of small diameter. 
  • While standing upright, maintain a 30 – 45 degrees electrode angle. 


Overlap in welding is when the face of the weld exceeds the weld toe. This condition involves the rolling of the weld metal until it forms an angle below 90 degrees. 

Overlap Causes

  • Wrong welding technique used. 
  • High welding voltage. 
  • Usage of large electrodes. 


  • Use a small diameter electrode. 
  • Proper welding technique. 
  • Medium voltage. 

Incomplete Fusion

Incomplete fusion forms when the welder fails to weld the workpiece properly. Then, the metal’s pre-solidification causes a gap in the material, which isn’t covered by the molten metal. 


  • Wong position of the bead. 
  • Shallow weld joint angle. 
  • Incomplete fusion can occur when there is low heat during welding. 
  • When the weld pool exceeds the arc. 
  • Incorrect torch angle and wrong electrode. 


  • Lower the rate of deposition. 
  • Proper positioning of the bead so sharp edges won’t come in contact with other beads. 
  • Adjust the travel speed and welding current to reduce the chances of incomplete fusion occurring. 
  • Correct positioning of the torch angle and electrode. 
  • The angle of the joint should be increased.

Incomplete Penetration

This defect can only be found in butt welds, where the metal’s groove is not adequately filled. Incomplete penetration can also be called an ‘Incompletely filled groove‘. 


  • Wrong electrode size. 
  • Low rate of deposition of the piece. 
  • Wrong welding technique. 


  • The welder should use the correct size of the electrode. 
  • Make use of the proper technique. 
  • High deposition rate of the workpiece. 

Necklace Cracking

Necklace cracking happens when the welder uses an electron beam welding on the weld area with improper penetration. Hence, the molten metal will not flow to the cavity. This process causes necklace cracking


  • Welding at a fast rate with an electron beam can cause necklace cracking. 
  • Stainless steel, tin alloys, nickel-base alloys, and carbon steel are prone to this defect. 
  • Incorrect technique. 


  • Adopting the right welding technique. 
  • Using the right quality materials for welding. 
  • Use a moderate speed while welding. 

Slag Inclusion

If the weld area has any slag, it will affect the metal’s weldability and toughness, decreasing its effectiveness. Slag can be formed at the middle of the welding turns or on the weld surface. 


  • When the current density is small, it doesn’t produce sufficient heat required to melt the metal surface, forming slag. 
  • Unclean weld edges. 
  • If the rod’s travel rate and welding angle are improper, it will form slag. 
  • Very fast welding speed. 


  • Higher current density. 
  • The proper rod travel rate and angle. 
  • Keep the welding speed at a moderate level, so the weld pool and slag do not come in contact. 
  • Properly clean the edges of the weld. 


What are different types of weld defects? 

Types of weld defects are weld crack, porosity, undercutting, spatter, overlap, crater, slag inclusion, incomplete penetration, incomplete fusion, and necklace cracking

What are the two types of welding defects? 

Welding defects are categorized into two and are External welding defects; these defects typically occur at the welded material’s top surface. The other classification is the Internal welding defects, which are formed under the material’s surface. 

Some defects under the permissible limits can be ignored, while others cannot be overlooked. 

What are the 5 types of welding? 

The five basic types of welding are; FCAW (Flux Cored Arc Welding), MIG (Metal Inert Gas) welding, TIG (Tungsten Inert Gas) welding, also called the GTAW (Gas Tungsten Arc Welding). MAG (Metal Active Gas) welding, GMAW (Gas Metal Arc Welding), and SMAW (Shielded Metal Arc Welding). 

Others include; gas welding, stick welding, plasma arc welding, linear friction welding, friction stir spot welding, and spot welding. 

What is a crater crack in welding? 

In welding, crater cracking is described as when the welder quits welding just before the project’s total completion, leaving a thin, wide depression close to the material’s end. Crater cracks can are visible in tack welded areas, i.e. where the welded passes are not entirely in contact with the tacks. A back-fill technique can be used to prevent this defect from occurring. 

What is a crack in welding? 

Cracking is a depression that happens due to incomplete welding, where the weld pool is not filled. Several forms of cracking occur due to shrinkage strains resulting from the cooling of the weld metal. If there is a restricted contraction, the strains will be in the residual stresses causing the cracks. 

Weld cracks are dangerous to a workpiece; they can cause high-stresses, leading to the piece’s sudden failure. 

What is undercutting in welding? 

Undercuts or undercutting are defects that occur on the upper surface of the welded area. They are classified under external welding defects. Undercutting are grooves that develop at the bottom of the metal near the weld’s root or toe. When a weld material is unable to fill in the groove section, this defect forms, resulting in a weak weld with cracks at the weld toes. 

What are the welding symbols? 

Welding symbols are languages used for effective communication between the designer and the welder. Welding symbols comprise arrows, sticks, or lines. These symbols are used to signify what the welder is meant to do in the project. 


These are the common types of defects that can occur in any welding process, with their causes and remedies alongside. When these defects are detected, you must take the appropriate measures to eliminate them to prevent unexpected material failure, which can be dangerous. 

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