Cracks:

Cracks are a serious welding defect as even the smallest cracks can worsen, which at some point will lead to weld failure. Weld cracks are mainly classified depending on how they form in the weld bead. 
Hot cracks: These phases can be torn apart due to solidification stresses (shrinkage stresses), which appear as cracks in the seam interior or seam surface
Cold cracks form after the cooling process of the weld metal. The weld crack can form hours or days after the metal’s cooling process.  

Probable causes:

• Using Hydrogen in shielding gas when welding ferrous metals. 
• Ductile base metal and the application of residual stress. 
• Rigid joints that constrain the expansion and contraction of the metal. 
• Use of high levels of sulphur and carbon.

How can I prevent welding cracks? 
• Selection of the correct welding materials including correct shielding gas (pure or mixture). 
• Preheating the metals and gradually cooling the weld joints. 
• Maintaining acceptable weld joint gaps. 
• Correct welding techniques
 

Porosity is the formation of pores in the weld pool resulting from gas bubbles that cannot escape. It is a discontinuity until it exceeds the specified limits and as such, is actually one of the most common welding defects when using shielding gas.  The volume of shielding gas if incorrect (none present, too little, too much) may lead to porosity, which reduces the strength of the weld. The most severe cases of porosity are formed as blow holes or pits caused by large gas bubbles becoming trapped within the weld pool.

Probable causes 
• Incorrect volume of shielding gas. 
• Unclean welding surface / contamination. 
• Wrong electrode selection. 
• Either too low or too high welding current. 
• Fast travel speed. 
• Damp flux / moisture build-up.

How can I prevent weld porosity?
• Proper gas flow rate setting to achieve the right amount of shielding. 
• Using reputable shielding gas suppliers with quality gas meeting specifications required 
• Cleaning the weld surface. 
• Using the correct welding electrode. 
• Preheating the metals before welding. 
• Adjustment of welding current and travel speed settings.
 

Undercuts can be the result of excessive arc length (voltage), thus spreading power density too small at either toe of the joint. Alternatively if insufficient filler metal is deposited into the weld resulting in a reduced cross-section where there are notches or grooves along the weld, increasing stress when the material is subjected to fatigue loading. This defect occurs at the toe of the weld or in the case of multi-run welds, in the fusion face. An undercut may come from continuous, intermediate and inter-run. In addition to this water, dirt and contaminants are prone to getting stuck in the groove(s) and this can accelerate corrosion in an already weakened area.

Causes 
• Incorrect weld parameters. 
• Incorrect electrode selection or wrong electrode angle. 
• High travel speed.

How can I prevent a welding undercut defect? 
• Smaller arc length, voltage, and travel speed. 
• 30 to 45 degree electrode angle. 
• Reducing the electrode diameter.

Overlap is the excess metal that spreads out around the bead causing the spread out filler metal to not fuse properly with the base metals. It is usually formed as a round shape over the weld joint.

Causes 
• Incorrect welding parameters. 
• Wrong selection of welding materials. 
• Improper preparation of base metals. 
• Incorrect weld techniques.

How do I prevent welding overlap?
• Correct weld parameters. 
• Use of proper welding techniques. 

A burn through is one of the common weld defects when welding thin metals. An open hole is exposed when the welding process incorrectly penetrates the entire thickness of the base metal, creating a burn through (also known as melt through).

Causes 
• High welding current. 
• Extreme gap to the root. 
• Not enough root face.

How do I prevent welding burn through (melt through)?
• Maintaining a proper root gap. 
• Control in the application of welding current. 
• Correct welding technique.  

Spatter is a "discontinuity" and becomes a welding defect once its size exceeds a specified limit. It occurs when metal droplets are discharged on the metal surface. It solidifies and becomes stuck on the metal surface once it cools down. In most cases, although spatter affects the appearance of the weld it does not alter the structural integrity. In general welding practice, spatters should be removed from the workpiece surface after welding, thereby adding to the overall cost of the weld. Larger fused spatter may cause hardened spots on the structure which can have impacts onto the mechanical properties and surface quality of the product. Minimising spatter eliminates this risk and increases efficiency within the welding process.

Causes 
• A common cause for spatter, when using short circuit mode is typically too much voltage
• With spray transfer it is typically not enough voltage as a rule of thumb. 
• Improper shielding gases. Using the right shielding gas is highly important to minimise spatter. 
• High arc length. 
• High welding current. 
• Using the wrong polarity may create excessive spatter. 
• Welder technique 
• Cleanliness and contamination control.

How do I prevent welding spatter?
• Selecting the best shielding gas and better shielding techniques. 
• Choosing the correct weld polarity and parameters. 
• Correct welding technique 
• Cleanliness of base material and oxide layers.

A weld bead that contains slag in its composition weakens and compromises the toughness and structure of the metal and is common to processes that use flux, such as stick, flux-cored, submerged arc welding, and brazing. Slag inclusion may occur either on just the surface of the weld metal or in between welding cycles.

Causes 
• Incorrect welding angle and travel speed of the welding torch. 
• Poor pre-cleaning of the edge of the weld surface. 
• Low welding current density resulting in inadequate heating of the metals. 
• Damp flux 

How do I prevent slag inclusion in my weld?
• Contamination prevention 
• Higher welding parameters. 
• Optimal welding angle and travel speed to avoid slag inclusion in the weld pool. 
• Consistent inter-run cleaning. 
• Correct welding technique.

Incomplete fusion is caused when the weld is not properly fused to the base metal, resulting in a lack of fusion. Incorrect welding can cause the metal to pre-solidify, forming gaps in the weld zone.

Causes 
• Low heat input results in metals not fusing. 
• Wrong joint angle, torch angle, and bead position. 
• Contamination 
• Incorrect welder technique 
• Incorrect inter-run cleaning or preparation.

How do I prevent incomplete fusion in my weld? 
• Higher welding current. 
• Correct travel speed. 
• Welder technique 
• Lower deposition rate. 
• Pre-weld cleaning and contamination control. 
• Pre-heating 

Incomplete penetration generally occurs during butt welding where the gap in between the metals isn’t filled completely through the joint thickness resulting in one or both sides of the weld joint not fused in the root.

Causes 
• Incorrect use of the welding technique. 
• Wrong electrode size. 
• Low deposition rate. 
• Incorrect setup

How do I prevent incomplete penetration of my weld?
• Using the correct welding technique and parameters. 
• Higher deposition rate. 
• Proper electrode size selection. 
• Welder technique