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Welding Discontinuities: Causes and Fixes


Welding Discontinuities: Causes and Fixes


Porosity, Incomplete Fusion, Inadequate Joint Penetration, Inclusions, Improper Arc Strike and Overlap are all welding discontinuities that can destroy the quality of your welds. 

In Order to help trouble shoot your welding and get back to dropping dimes, Read the breakdown of each of these discontinuities and how to adjust your welding and welder settings to combat them.

1. Porosity

Porosity can be a very frustrating discontinuity and is characterized by gas bubbles remaining trapped in the molten weld puddle as it cools, leaving an ugly bubbled, porous weld puddle. Depending on the severity of porosity, this can fail a weld and cause a weakened weld bead.

Causes and Fix :

Gas Flow: Check to make sure your Flow Meter is set to the proper CFH as well as all gas lines are free from leaks. (See Checking for Welding Gas Leaks)

Base Material Contamination: No matter what welding process your using its important to make sure the materials your welding are clean from any oils, dirt, and other contaminants.

To Long of an Arc: Having to long of an Arc or contact to work distance will cause insufficient Gas coverage resulting in porosity.

Bad Welding Gas: Not as common but can still be a culprit. Bad welding gas can come from old welding bottles or gas bottles that are not completely emptied before being refilled.


2. Incomplete Fusion

Incomplete Fusion refers to two types of weld discontinuities. The first is lack of fusion between the weld puddle and side wall of weld joint. The second discontinuity is called Cold Lap which is when the filler metal and base metal do not fuse sufficiently.

Causes and Fix

Improper Machine Set Up: Amperage and Wire Speed can play a roll in lack of fusion. Be sure to refer to your welders Amp/Wire Speed Guide normally located on the inside panel of MIG welders.

Travel Speed: Traveling to fast during your weld can cause lack of fusion. Remember to lets the weld puddle fill in before moving forward.

Travel Angle: The angle of your electrode can directly effect weld puddle fusion.

Oxide Layers: Metals like Aluminum have oxide layers that must be broken up in order for proper weld fusion. Wire brushes or wire wheels can help remove this layer. (See Welding Aluminum for more information)

3. Inadequate Joint Penetration

Inadequate joint penetration is  characterized by a lack of fusion between the base materials resulting in a stress point that can fail due to its weak characteristics.

Causes and Fix

Preheating: Certain materials and metal thicknesses will require a preheating temperature so that you can get the proper joint penetration for your weld.

Arc Angle: Be Sure your Arc angle is correct for the weld you are performing. Material thickness, joint design, and many other characteristics can play a roll in Arc Angle.

Amperage: Machine amperage setting must be set to the thickness material you are welding but should also just be a starting point for you as playing with the settings can help you dial in a proper weld bead profile.

Joint Design: Even if you have the settings dialed in, sometimes a poor joint design can cause a welder to have inadequate joint penetration. Proper Preparation of your weld joint is just as important as knowing how to weld it.

4. Inclusions

Welding Inclusions can be characterized by the entrapment of slag or other foreign materials between the base metal and the weld puddle. These inclusions can cause the weld to be structurally compromised. 

Causes and Fix

Material Preparation: Cleaning your base metals form all rust, metal scale, and slag will help reduce the risk of Weld Inclusions.

Proper Weld Technique: Welding technique such as arc manipulation can cause inclusions if done incorrectly.

Cleaning Previous Weld Beads: When welding multiple passes it is important to wire brush all remaining slag from the previous weld bead.

5. Improper Arc Strike

While striking an arc it is possible for one to strike it outside of the joint location, leaving behind small discontinuities that can cause cracking or failure.

Causes and Fix

Improper Techniques: Lack of knowledge or carelessness can lead to a bad arc strike. Be sure to locate where you want to strike your arc before welding.

Bad Ground Clamp: Having a poorly grounded work piece can allow for poor and wandering arc properties. Be sure your ground clamp is connected to clean metal and the wires on the lead are not damage or old.

6. Overlap

Overlap in a weld joint is characterized by on excess or overflow of weld material for a certain weld joint. Often this discontinuity will cause a lack of joint fusion.

Causes and Fix

Arc Angle: Arc angle will directly effect where the filler metal is going to be forced.

Travel Speed: Traveling to slow during a weld can cause overlap on your weld joint. In order to fix this try running practice welds at different travel speeds to find the sweet spot.

Improper Weld Sizing: Knowing the size of a weld needed for specific welding applications is critical. Reading blueprints and understanding weld symbols is crucial.



    Welding discontinuities can be very frustrating when learning to weld but its part of becoming a great welder. A great welder can figure out why they are getting discontinuities and how they can fix them. I hope this post helps clear up any questions you may have about welding discontinuities and encourage you to leave comments and questions below.











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