Welding is a highly trending trade in the current world. Welders normally create products holding lots of responsibility. When welding is not correctly done, the result can be quite dangerous since different parts can easily break and people can get injured.
One common weakness that comes with welding is porosity. In this article, we will be looking at causes of porosity in welding and how to prevent it.
Porosity refers to a metal contamination form. It can lead to a bubble filled and weak weld that never meets code since it can make structures weak that can later collapse.
Porosity starts when weld pool that is in liquid form absorbs and traps hydrogen, nitrogen, and oxygen. When the weld solidifies, the gases remain inside the weld metal leading to cavities.
There are different types of porosity. The types include:
- Surface breaking pores- Pores that break the surface
- Distributed porosity- Pores placed through the weld
- Wormhole- Pores that are elongated showing up the resemblance
- Crater Pipes- Shrinkage cavity at the weld run end
Causes of Porosity in Welding
It is important that you know the causes of porosity. There are different causes of porosity. In this section we will be looking at some of the common causes:
- Gas inside the cylinder
- Air drafts
- Moisture from morning dew, condensation, and water
- Weld spatter that obstructs the opening of the nozzle
- Wrong angle between the FCAW, GMAW, or SMAW guns and the joint
- Improper storage and care of the equipment
- Contamination of grease, glue, sweat, oil, and paint
- High flow of gas
- Oxidation as a result of welding over rust
Apart from this list, it is essential to know that every type of porosity listed in the article comes with its own unique set of causes.
Surface Breaking Pores and Distributed Porosity
High gas flow rate, gas line leaks, draught, and excessive turbulence in the weld pool will most likely lead to porosity. For instance, when the shielding gas contains a mere 1% of air entrainment, it will always lead to distributed porosity. However, anything that is higher than 1.5% of air entrainment will always lead to surface breaking pores.
When welding materials that have a surface coating for example primer paints or zinc coating, there is always a great chance of porosity since the coatings do generate huge amounts of fumes whenever welding.
Excess gases forming in crevices are the main cause of wormholes. Just like in distributed porosity, primed vertical members in the T-joints will have to meet the recommendations of the manufacturer which is in most cases 20µm.
Crater pipe can always form during the last solidification whenever there is gas porosity. In most cases, shrinkage is one of the main causes and the conditions available whenever volume changes take place during liquid to solid transformation lead to its exaggeration.
Rapid solidification in the weld pool takes place when the welding arc is completely extinguished. When you stop welding wire from getting attached to the weld pool before stopping the welding arc, there are high chances a crater will form.
Tips on How to Prevent Porosity
Considering all the issues that can lead to porosity, it seems quite impossible to prevent it from happening. Cluster porosity in welding can be quite easy to avoid. In fact, it gets much easier as you gain more experience in welding.
One of the easiest ways of avoiding porosity is taking precautions that all welders need to be practicing. Some of the precautions include:
- Ensuring all your materials is always clean
- Checking the flow of gas
- Inspecting the equipment to ensure it is working well
- Inspecting the conditions at the workspace
- Understanding the right welding procedure
Studying and memorizing all the causes listed above is one easy way that will ensure you avoid porosity from appearing in your welds. With this, you will be in a position of dropping the porosity rate that is produced.
Apart from the above prevention tips, there are numerous other things you can always carry out depending on the porosity type.
Source of Gas
Get the source of gas and remove it. There are chances the gas is coming from air leakage, wrong application, draughts, turbulences of weld pool, filler deoxidant composition, and high flow of shielding gas. It is important that you check and have all these issues and fix them accordingly.
Ensure you dry the electrode and the flux according to the recommendations of the manufacturer and clean the workspace surface.
Before you start welding, ensure that you clean the edges of the joint and check the wieldable primer thickness.
Fixing Porosity in Welds
Despite all the methods you can use to fix porosity, there is always that chance of it appearing on the welds. However, you need not worry a lot since you can fix porosity in aluminum welds under certain circumstances.
You will have to detect porosity presence by using magnetic inspection techniques or penetrants like ultrasonic inspection or radiography. The small pores especially those in thick areas are quite difficult to detect.
You cannot fix the porosity itself, instead, you can fix the weld when you remove the localize gouging or grind it out. However, this is only when you manage to contain porosity.
When it is widespread, you will have to remove the whole weld, start preparing the joint once again and follow the welding procedure while welding.
What Amount of Porosity is Acceptable in a Weld?
There is never a general sound or a clear answer to this question since it depends on the construction code of your welding. The American Welding Society requires the following:
- Any linear inch of visible porosity should be 3/8 inches (or 9.4mm) or less in diameter
- 3.4 inches (or 19mm) in a 12-inch length of the weld.
In case you are in doubt, you will have to check the code of the welding construction and redo the weld again.
Porosity is a popular defect that most welders encounter whenever they are welding. There are lots of things that can cause porosity. The good this is that its prevention rate is 90% effective. It is also possible to undo several rejects to meet the welding codes. The most important thing when it comes to porosity in welding is to be knowledgeable, aware, and honest in any welding work you are doing. Fix all the mistakes you make.