In this post you'll learn
Welding defects are one of the most subtle ways an asset or equipment can be at risk. All welded metal will experience fatigue and wear as time goes on. Due to using the incorrect welding process or the wrong welding technique, the earlier they’re caught, the easier it is to fix them, and there is less risk of a leak or collapse. Even something as simple as an incomplete fusion can be catastrophic. The joint design of a weld is vital for any industry.
Take, for example, what happened in 1980 at the Alexander L. Kielland platform. It is considered the worst disaster in Norwegian waters since World War II, and it was all caused by a “small 6 mm filler weld with poor profile had precipitated the crack.”
Types of Welding Defects
Now that you know how to reveal welding defects, we’re going to learn to identify what kind of weld defect we are dealing with. Each has its own characteristics and needs a different approach to repair.
Slag Inclusions
What it looks like
Welding slag is a form of vitreous matter which can be produced as a byproduct of stick welding, shielded metal arc welding, submerged arc welding, flux-cored arc welding, and electroslag welding, or even the wrong weld current during fusion.
What it can cause
Slag inclusions do not contribute to the strength or protection of metals one after being welded. It is necessary to remove them, as it is waste inside the weld metal. Its removal is necessary as it will inhibit the inspection of the weld area, will have a bad visual appearance, will need to be removed in case a second layer or pass is required, and lastly to clean and clear the surface for coatings (paint) or oil.
What causes it
Slag is formed when flux melts in or on top of weld beads by wrong electrode technique. It is not uncommon for some areas to become embedded within the solidified metal if for some reason it did not float to the top of the molten metal where they will be visible and not affect the structural integrity of the weld.
How to repair it
Removal is usually done with manual or power tools. Manual tools usually include a chipping hammer.
We recommend using our TFT Milling Discs to clean the surface for weld preparation. All milling discs, whether for aluminum or steel, can be attached to most angle grinders.
Their benefits include no abrasive residues, no smearing, no kickbacks, no stress in the metal through overheating and a very long life. They are considered to be perfect for weld preparation.
Porosity
What it looks like
Porosity is the presence of cavities within the weld metal. The forms it takes can be:
- distributed porosity
- surface-breaking pores
- wormhole
- crater pipes
What it can cause
Porosity causes reduced strength and failures in some cases due to fatigue.
What causes it
Among the possible causes of porosity in welding we can include:
- Substances in the surface including moisture, grease, oil and surface contamination in general.
- Poor gas shielding originated from Nitrogen and oxygen absorption in the weld pool.
- Surface coatings. As the welding process takes place, large amounts of fumes may get trapped.
How to repair it
Remove porosity with an angle grinder, using the right wheel attached. For explosive environments, we recommend using a non-sparking disc, such as the TFT Milling Disc.
Undercut
What it looks like
An undercut is a grove left in the base metal unfilled by filler weld metal during fusion. It happens along the toe lines of a weld. This is easily noticeable in the joint design at hand.
What it can cause
Fatigue crack propagation and failure.
What causes it
This is clearly a welding technique issue. If the temperature is too hot near the free edges, parent metal of previous weld metal particularly near thinner and free edges. It can also be caused by erratic movements, electrode error, holding too long an arc, arc blow, or not pausing long enough on the toes of the weld.
How to repair it
You need to remove the weld seam with a grinding wheel. Once removed, you can start over.
Weld Crack
What it looks like
Separation of the filler weld metal or discontinuity in the and between the base metal and filler metal. Types may include longitudinal, transverse, crater, throat, toe, root, underbead, hot and cold
What it can cause
Failure and crater crack propagation.
What causes it
Some of the causes are port parts fit-up, rapid cooling, contamination. Most longitudinal and centerline cracks are caused by improper width-to-depth ratio, a low melting point of tramp elements in the base, and concave surfaces or even using the wrong electrode.
How to repair it
There are 2 options: Carbon arc gouging or mechanical removal by means of an angle grinder.
Incomplete Fusion
What it looks like
Lack of fusion happens when the weld does not fuse with the base metal.
What it can cause
Reduced strength and failures.
What causes it
Some of the causes of incomplete fusion are:
- Improper welding fusion
- Inability during the welding process to elevate the base metal or previously deposited weld metal to its melting temperature.
- Travel speed too slow which allows the weld to roll over the edges, This will trap slag between the bead and base metal.
- Wrong electrode angle which pushes the weld metal over the slag.
- Travel speed too fast or amperage setting too high.
- Arc length too long allowing the weld to be deposited randomly.
How to repair it
Like all the other welding defects, remove the bad weld, and reweld.
Incomplete Penetration
What it looks like
Incomplete penetration happens when the groove being welded is too narrow and the weld metal does not reach the bottom of the weld joint.
What it can cause
Reduced strength and failure. It’s similar to incomplete fusion.
What causes it
Mainly improper joint preparation, insufficient heat input as well as improper shielding gas mixture and welding wire diameter. Even the wrong travel speed can cause it.
How to repair it
Incomplete penetration must be removed by mechanical means. Using an angle grinder and opening up the groove to reveal the filler metal to remove.
Spatter
What it looks like
Molten metal or non-metallic material that is scattered or splashed during GAS welding or ARC welding process. These small or large particles of hot material, also known as droplets, are noticeable in the joint design and may stick to the base material and surrounding metallic material and in some cases may even fly and fall on the workbench, or surrounding area.
What it can cause
Spatter that accumulates in the nozzle can detach and damage weld beads. It can also cause accidents to the User due to accumulations of spatter projections in the nozzle, which can cause render the cords unusable as well.
What causes it
Some of the causes include the following:
- Weld pool too hot or too cold.
- Shielding gas being used.
- Wire feed to high or too low.
- Poorly wound spools of welding wire.
- Welding wire stick out.
- Poor connections to the ground clamp.
- Incorrect welding wire storage.
- High humidity of weld environment.
- Weld contamination including dirty surfaces, rust, oil, paint and mill scale.
How to repair it
In most cases, it can be reduced. To eliminate after welding Mechanical removal by means of an angle grinder is ideal. To clean up the spatter, a single-sided milling disc is an ideal option.
How to Reveal Welding Defects
In any case, the way to repair is to first remove the weld bead. Normally, you’d use a grinding wheel to remove it. Instead, we want to show you how we use our TFT Milling Disc to easily remove weld metal from the surface.
Instead of grinding or cutting, you basically shave off the weld bead, with no abrasion and no smearing. This easily exposes any welding defects present in your structure.
The idea behind the milling discs is to use them in your manufacturing process in order to maximize the quality of your surface preparation. They can also be used for repairs in order to remove any old weld metal in the seam. There are many ways to get this job done, and these are some of the best tools in the market.
How to know if it’s a Weld Discontinuity or a Welding Defect
A weld discontinuity is easy to recognize because it looks like an interruption of normal flow. It is also known as a weld imperfection, and it can be found in the weld metal or the parent metal.
A discontinuity happens in the weld metal due to the wrong welding pattern or welding technique. It can differ from the weld bead shape and thickness and ultimately, the quality.
In general, a discontinuity should be avoided and dealt with, but they are marginally less serious than a welding defect. Nonetheless, if you do find a weld discontinuity, you need to fix it.
That said, a group of weld discontinuities can become a weld defect, if they exceed the limits stated in your project. This goes in accordance to your country, the material and the type of environment you are in.
Ultimately, the most effective way to inspect a welding job, especially in tight spaces, is using a welding camera. Here are some video examples of how that works.
Identifying Welding Defects Before it’s Too Late
It is impossible to overstate the importance of catching welding defects in time. Even the slightest defect can be catastrophic.
From taking care of the welding technique, down to the welding current and supervision, welding is a complex craft that requires the utmost attention.
Investing in the right tools that will make it easy and safe to get the job done. It is crucial for companies in the oil, gas and mining industries to understand how to identify the most common welding defects, so they can act.
Contact us to know more about how we can help you keep your workplace safer.
