The Welders Guide to Defects and Remedies

Learn about different types of weld defects, causes and their respective preventions 

Weld defects are more than just surface imperfections and are like the hidden troublemakers that occur during the welding process and can drastically affect the reliability and performance of a joint. From poor technique to incorrect parameter settings to mismatched filler metals to unprepared base materials, a lot can go wrong. These defects not only can affect the quality and shape of the weld, but also can lead to re-work, lower productivity, wasted time, reduced profitability, etc. The good thing is that most of the weld defects are preventable, with the right attention to detail and know-how. 

Types, Causes and Remedies of Weld Defects:

1.    Porosity 

Porosity refers to the tiny gas pockets or cavities that form in the weld metal when trapped gases fail to escape during solidification. They may appear small but can seriously weaken the weld and compromise the quality.  

Causes: 

• Contamination of base metal due to dirt, oil, grease, rust, paint, and mill scale
• Presence of moisture in base metal and welding consumables 
• Inadequate gas shielding coverage 
• Impure and damp shielding gases 
• Improper weld parameter setting/technique – higher stick out used during GMAW process, higher arc length used during SMAW process or higher weld travel speed 

Remedies: 

• Use clean base metal 
• Re-dry welding consumables as per manufacturer recommendations, use dry plates or pre-heat base metal 
• Set optimum gas flow rate, check gas hoses for no leaks, ensure the spatter clogs are removed from the gas nozzle, and ensure contact tips are not too recessed or extruded
• Ensure the purity of gases and use heaters while using 100% CO2 gas
• Ensure appropriate stick out of 15 to 20mm is maintained during the GMAW process
• Ensure short arc length is maintained during the SMAW process, and try with reduced weld travel speed during the welding process

2.    Spatter 

Spatter refers to tiny droplets of molten metal that are expelled during welding. These particles often land on the base metal or the gas nozzle, resulting in surface irregularities that can compromise weld quality, diminish visual appeal, and increase cleanup time.

Causes:  

• Contamination of base metal due to dirt, oil, grease, rust, paint and mill scale
• Damp electrodes and welding wires
• Erratic wire feed 
• Worn out / incorrect contact tips
• Incorrect polarity
• Wrong shielding gas selection and inadequate gas shielding coverage 
• Improper weld parameter setting/technique, such as high arc length, welding current or improper torch angle 

Remedies: 

• Use clean base metal 
• Re-dry electrodes and ensure storage of welding consumables as per manufacturer recommendations 
• Ensure the feeding mechanisms are proper and wire feeding is smooth in the GMAW process
• Use appropriate contact tips for the specified wire size and replace whenever required 
• Ensure appropriate polarity is used for the specific welding consumables
• Choose the correct shielding gas combination suggested for the wires and set the appropriate gas flow rate 
• Ensure appropriate welding current, reduced arc length, and proper torch angle during the welding process

3.    Slag Inclusions 

Slag inclusions refer to the non-metallic particles trapped in the weld metal, usually between the weld passes, causing weak spots and poor weld quality. 

Causes:  

• Slag runs ahead to the front side of the weld pool during welding 
• Insufficient root opening, too deep and narrow welding groove 
• Improper slag removal between weld passes / layers  
• Incorrect welding parameters and techniques, such as low current, fast weld travel speed, incorrect welding angle or improper cleaning of base metal 

Remedies: 

• Ensure the torch angle is proper, the welding current and travel speed are appropriate 
• Ensure an adequate root opening, removal of slag from the previous weld beads, and choose the electrodes or wires having good slag release 
• Carefully remove the slag between weld passes, specifically at the edges of the base metal where the slag may be trapped. 
• Ensure appropriate welding current, reduced travel speed, proper torch angle and cleanliness of the base metal to avoid slag inclusions

4.    Undercut 

Undercut is a welding defect characterised by a groove or notch formed along the edge of the weld. It occurs when the weld metal fails to adequately fill the joint, resulting in a depression at the toe of the weld that can weaken the joint and reduce its overall structural integrity.

Causes:  

• Improper weld parameter setting and poor welding techniques, such as too high weld current or weld travel speed, incorrect torch angle, long arc, or excess weaving 
• Incorrect usage of gas and inadequate gas shielding coverage 

Remedies: 

• Set appropriate current
• Use proper electrode angle, appropriate arc length, with a reduced travel speed
• Choose the correct welding technique that doesn’t involve excessive weaving
• Choose shielding gas having the correct composition for the specific material type. Set the appropriate gas flow rate. Avoid turbulence due to excessive gas flow rate 
• Use multi-pass technique

5.    Lack of Fusion 

Lack of fusion is a welding defect that occurs when the weld metal fails to adequately fuse with the base metal or preceding weld passes, resulting in discontinuities and weakened joints. This defect can manifest in various forms, such as lack of root fusion, interpass fusion, or sidewall fusion. When fusion is incomplete, the mechanical strength and structural integrity of the weld are significantly compromised.

• Lack of Sidewall Fusion: Occurs between the weld and the parent metal along the sides of the weld.
• Lack of Inter-Run Fusion: Occurs between adjacent weld runs in a multi-pass weld.
• Lack of Root Fusion: Occurs where the weld metal fails to fuse with the base metal at the root of the weld.

Causes:  

• Improper weld parameter setting and poor welding techniques, such as too fast weld travel speed, incorrect torch angle or too low weld current
• Incorrect size of electrode/wire diameter for the material thickness
• Surface contamination

Remedies:

• Use proper electrode angle and reduced weld travel speed
• Set the appropriate current with the appropriate arc voltage
• Ensure the edges/root of the base metal are properly fused, and sufficient welding metal is deposited during welding
• Use correct electrode size/wire diameter for proper fusion of the base metal
• Use clean plates 

6.    Lack of Penetration 

Lack of penetration is a welding defect in which the weld metal fails to extend through the full thickness of the joint. This unfilled portion of the joint compromises the weld's internal strength and can influence its load-bearing capacity.

Causes: 

• Incorrect weld parameter setting and poor weld techniques, such as too low current, improper electrode angle, too fast weld travel speed or longer arc length 
• Too small root gap 
• Large Root face 
• Improper joint fit-up/misalignment 

Remedies:

• Increase welding current, decrease travel speed and use short arc length/lower stick out
• Ensure the appropriate electrode/torch angle during welding  
• Use the Pull technique instead of the Push for better penetration 
• Increase root gap and reduce root face 
• Ensure no misalignments in the joint fit-up 

7.    Weld Cracks 

Weld cracks are fracture-type discontinuities that develop in the weld metal or the adjacent base metal. These defects significantly compromise weld integrity and can propagate under load. Based on their origin and orientation, weld cracks are classified as follows:

Hot cracks: These form in the weld metal during the solidification phase at elevated temperatures, often due to solidification shrinkage or metallurgical factors.
Cold cracks: These occur after the weld has cooled and solidified, typically as a result of residual stresses, hydrogen embrittlement, or poor joint design. Cold cracks are also referred to as delayed cracking or hydrogen-induced cracking.  
Longitudinal cracks: These develop parallel to the weld bead and may occur along the centerline or edges of the weld. 
Transverse cracks: These run perpendicular to the weld bead and are usually associated with high restraint and residual stress.
Crater cracks: These are short, star-shaped cracks that form at the end of a weld bead where the arc is extinguished abruptly without sufficient fill.

Causes (Hot cracks):

• Low melting point phases due to P, S, Cu (parent metal)
• Insufficient weld size
• Unfavourable joint geometry – width/depth ratio <1
• Rapid cooling rate
• Poor fit-up / large root gaps
• Tack welds or root passes are not sufficiently strong
• Crater crack

Remedies:

• Clean parent material or buffer plate edges
• Reduce voltage/travel speed
• Increase joint angle, lower welding current
• Reduce cooling rate through preheat
• Ensure proper fit-up and reduce root gaps
• Apply stronger tack welds  
• Move the electrode back to fill up the  crater and increase the crater fill time in the power source

Causes (Cold cracks):

• Hydrogen Embrittlement
• Residual Stresses
• Susceptible microstructure 

Remedies:

• Prefer low hydrogen filler metals and ensure proper re-drying 
• Ensure the appropriate PWHT / stress relieving
• Ensure the appropriate preheat and inter-pass temperature 
• Reduce the cooling rate 
• Ensure proper weld techniques with appropriate weld parameters and sequence

Weld defects—whether porosity, cracks, undercuts, slag inclusions, or other imperfections—can seriously undermine the quality and safety of a welded structure. Fortunately, the majority of these flaws are preventable. The key lies in mastering the fundamentals: understanding common defect types, knowing their root causes, and applying proven techniques to avoid them. By using the correct welding parameters, maintaining proper procedures, and conducting rigorous inspections, fabricators can minimise errors, reduce costly rework, and consistently deliver strong, high-integrity welds that stand the test of time.