Porosity in welds is a common weld defect that can easily occur. Luckily it is normally straight forward to fix and remove from the welding process. So, what is porosity in welds?
What is Porosity
Porosity is the presence of a void or voids in the weld bead. Porosity in welds is a defect and is an undesirable result as it reduces the strength of a weld. Voids form when nitrogen, oxygen and hydrogen diffuse into the weld pool.
During the solidification phase, these gases are released, which lead to them becoming trapped in the metal. Hydrogen tends to be the main gas entrapped which leads to porosity.
The hydrogen source can range from moisture on the electrode to the presence of grease and oil on the workpiece. The nature of gas entrapments gives the voids a spherical shape. Additionally, they may be slightly elongated, giving them a cylindrical shape.
Types of Porosity
There is a range of different types of porosity that take up different shapes and sizes. We will quickly cover the main types of porosity:
- Distributed Porosity – As the name suggests, the voids are evenly distributed within the weld bead
- Surface Breaking Porosity – This type of porosity builds on distributed porosity. Surface breaking takes it one step further as the voids present in the weld can be seen at the surface of the weld.
- Wormholes – Wormholes are elongated voids that take up a cylindrical shape which is a result of a large volume of gas becoming entrapped.
- Crater Pipes – Crater pipes occur during the final solidification of the weld pool and are frequently associated with porosity. Learn more about craters here.
How Can We Prevent Porosity?
As discussed in my welding article, the shielding gas acts as a barrier between the molten pool and the atmosphere, preventing contamination. If the gas flow is too high, it risks disturbing the surrounding air resulting in mixing. Another way of preventing porosity is ensuring the surfaces are clean.
Although this may seem obvious and easy prevention, it can sometimes be underestimated. Grease and oil are present in many engineering applications, so we must clean the surface. Also, moisture isn’t such an obvious visual. Wiping the equipment to ensure it’s dry is another cleaning activity to help reduce porosity.
Summary
Porosity is a welding defect that can occur as a result of many consequences. It commonly stems from contamination, be it grease and oil or gas contamination. Contamination is reasonably straightforward to solve once you know it’s there, meaning porosity prevention isn’t difficult.
I hope you have enjoyed this post. Please leave your questions and feedback below!
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