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.
Burn-Through
What it looks like
A burn-through looks like holes in the base material, as the name suggests. The arc creating holes or even thinning down the material is common.
What it can cause
Burn-through weakens the structural integrity of the base material. In welds that are expected to be sealed such as pipe welds or storage tanks, burn-through can cause leaks.
What causes it
Burn-through commonly occurs while welding thin sheets of metal. Powerful welding machines, incorrect adjustments, or improper technique can cause the weld to burn through the metal, creating a hole.
How to Repair It
If possible, the best solution to fix a burn-through is to cut off the section and re-weld. However, if re-welding is not an option, it can be fixed by adding filler materials or molten metal. The reinforced surface must be grinded smooth.
Distortion
What it looks like
Distortion can be spotted by comparing the intended dimension against the achieved ones. If the geometry of the part that’s being welded seems altered or changed, this is probably due to heat distorting the material.
What it can cause
can alter the intended shape and dimensions of the welded structure. This can lead to weld edges not being aligned and shape alterations. Edges which are not properly aligned causes welds no join improperly, leading to structural integrity issues. Shape alterations can cause similar issues but specifically for pipelines, altered shapes create improperly sealed joints.
What causes it
Distortion is mostly a technique issue. When a torch that is generating high levels of heat is applied on base material, thermal dispositions occur. Welders are expected to know the effects of thermal dispositions on the base material. Proper breaks must be taken in between welding sessions to allow the material to cool down. Torches that are way too overpowered for the intended job must not be used.
How to Repair It
Minor distortions can be fixed by reshaping the material with hydraulic presses or even with hammers by hand. However, parts that are distorted beyond repair must be discarded.
Brittle Weld
What it looks like
Brittle welds can be identified by stacked granular structure. This structure is commonly visible and presents an identifiable texture.
What it can cause
Brittle welds lack ductility. Structural elements that are expected to endure high-stress or loads must be inspected against brittle welds. It can cause cracks and ruptures on the weld points, causing structural integrity issues.
What causes it
Sudden changes in ambient temperature, presence of excessive heat or use of incorrect equipment such as wrong electrodes and torches are some of the most common causes of brittle welds.
How to Repair It
Unfortunately, there is no way to implement ductility to an existing weld thus, the only possible option is the perform the weld again by using correct equipment and techniques under proper ambient conditions.
Crater Cracks
What it looks like
Crater cracks resemble craters as the name suggests. Crater-like imperfections can be spotted around the edges of the weld.
What it can cause
As we studied in the distortion section, base material is exposed to heat which causes it to expand. A weld that’s paused midway then continued after the base material cooled down completely, puts pressure on the completed section of the weld since the material returns to its original size after the removal of heat. This stress can cause fractures or cracks due to negative thermal disposition.
What causes it
They are often caused by abrupt termination of the welding process. Sudden changes of heat on the base material surface can lead to crater cracks. Another possible cause of crater cracks is inadequate reinforcement. Just as the base metal, the molten metal filling the weld shrinks after removal of the heat. The welder should account for it and implement additional volume to compensate for the shrinkage.
How to Repair It
The only reliable way to fix a crater crack is to clean the area with a grinder. Then decontaminate and clean it then re-weld.
Inadequate Reinforcement
What it looks like
Edges of the two base materials need to be filled for the weld to be strong. Inadequate reinforcement is the case of the edge not being filled properly. Welding beads with less volume and smaller dimensions than recommended standards must be inspected as signs of inadequately reinforced welds.
What it can cause
As mentioned in the previous section, inadequate reinforcement can cause crater cracks. In addition, lack of adequate filler compromises the integrity of the weld.
What causes it
It’s a technique issue. Welder should be informed about the required amount of reinforcement in order to create a seamless, durable weld.
How to Repair It
In some cases, the weld can be topped off with additional material. However, this does not ensure a seamless and fully integrated weld. The most reliable solution would be to perform the weld again.
Overlapping
What it looks like
Overlapping welds can be seen as inconsistent beads stacked on top of each other. Even though gaps in welds are not desired, total overlaps cause the previous filler to melt down. This creates lumps and beads that are out of shape.
What it can cause
This can lead to structural issues as well as compromising the seal. It’s difficult the detect what sort of issues that overlapping beads might cause under the surface without the implication of destructive and non-destructive methods.
What causes it
Overlapping is caused by welder error. Some levels of overlapping are crucial for a seamless and durable weld. However, the degree of overlapping should not be excessive.
How to Repair It
If there is no below surface damage, the inconsistent beads can be grinded down and re-welded. However, if the inconsistency is deeper, then a re-weld must be performed.
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.
Cutting and Grinding Wheels to reveal welding defects
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.
