Welding defects are simply defects or unacceptable imperfections in the welding process. This article holds the elaborative analysis of different welding defects, its various types, and the subsequent causes and remedies.
Let’s delve into the broader perspective of varying welding defects.
Let’s try to understand the basics of welding defects. Welding is a process that helps to join materials, basically metals or thermoplastics with the help of the heat that makes the different parts to melt.
Subsequently, the parts get cooled and cause fusion.
Though this process is quite efficient, different welding defects affect the longevity and performance of welding.
These defects are quite complicated, but the holistic understanding of their causes and remedies can prevent the low quality and life of welded parts.
Longer lasting and high quality of the weld is the core need.
With the proper detection of these welding defects, one can easily deduce the severity and take appropriate action.
Even a mere defect that doesn’t hold much importance can easily make a welded structure ineffective to work as per need.
Welding Defects Definition
Welding defects are the defects that generate due to numerous reasons such as poor or faulty techniques used by the unskilled or inexperienced welder or due to the core difficulties in the welding process.
However, it is not only the manual approach, but the welding defects also persist in automated robotic welding due to different reasons such as parameters abnormalities, the inadequate supply of gas and water etc.
The parameters that define an excellent weld depends upon the optimal fusion between the filler materials and the shape acquired with apt penetration.
This is one of the common defects that occur while welding. It is pores or cavities that generate because of the entrapment of non-metallic and gaseous material during the process of solidification after welding.
This defect generally causes harm to the welded part based on size, orientation to stresses and quantity.
If porosity occurs in the weld center, then it doesn’t cause much fatigue, though it is capable of reducing the static stress carrying capacity of the welded part as well as the core weld.
Depending on the formation of Porosity, it can be as follows,
These are spherical shaped small cavity,
These are generated due to the trapped gases in the weld metal.
There are many gases like oxygen, hydrogen, nitrogen, water vapor, helium, argon, carbon monoxide, carbon di oxide etc. may be present in the molten metal which cause porosity.
If the trapped gasses are tubular form or cylindrical or elongated cavities during solidification, then that porosity is called wormholes.
Wormholes can appear in single or in groups on the weld surface.
Porosities which occurs on the surface and break it.
These type of porosity basically localized group of pores.
In this type, pores are aligned.
Uniformly distributed porosity,
In this type, pores are distributed uniformly in the welding area.
If porosity is seen in the weld face, it is called pit porosity.
In this case, porosity is in the sub-surface,
It is detected, by fracture or radiograph tests,
It is not extended to the weld face and called as “blowhole.”
It forms during final solidification of the weld pool,
It occurs due to gas porosity.
It forms due to shrinkage on weld pool solidification.
Apart from the entrapment of gas or any other non-metallic materials porosity occurs due to some other reasons also such as,
Too short arc gap,
Poor welding technique,
Problem in gas shielding,
Using a longer arc,
Moisture presence on weld zone,
Presence of contamination on the surface,
If electrode is not coated properly,
Improper surface treatment.
Oil or rust presence on the surface,
High gas flow,
This is a defect that is not acceptable at any point. It can be controlled through different ways such as,
Improved welding techniques,
Optimal selection of filler materials,
Proper selection of electrodes, and it shall be dry, coated,
Proper maintenance of the work area where welding is operational,
Minimized speed that allows the gas to escape,
Cleaning or surface treatment of the materials prior to welding,
Less arc distance, so that gasses can be escaped,
Proper shielding, gas flow meter can be used to check the pressure and flow adjustment.
Welding Defects Undercutting
When it comes to one of the severe welding defects, then undercutting takes the prominent place. It is an abnormality that can be summed up as an unfilled groove that exists along weld edges.
This occurs due to different problems such as,
Incorrect electrode angles,
Improper electrode selection,
Improver welding techniques,
Using large electrodes,
Improper gas shielding,
This defect can be prevented with the help of the following,
Maximum attention towards the whole welding process by attaining basic improvements in the entire welding process,
It can be repaired with the help of welding the grove with comparatively smaller electrodes,
Selecting suitable electrodes, with proper angle,
Optimize the arc length,
Controlling the current,
Gas shielding should be proper,
Welding Defects Concave and Convex Welds
When the weld attains different shapes, then it is known as misshaped welds. These defects constitute mainly two of the shapes,
Excellent welding doesn’t acquire both shapes.
Lack of reinforcement or excessive concavity prevents the weld from getting suboptimal throat thickness as compared to the desired weld size.
Apart from that convexity provides below par level weld contour where there is multilayer welding the probability of slag inclusions due to this while it also causes a local notch effect or poor stress capability in the finished weld.
Causesof Concave and Convex Welds
It occurs mainly due to,
The amalgamation of incorrect or improper speed and
Remediesof Concave and Convex Welds
This defect can be prevented with the help of the following,
Using proper weaving pattern,
optimal current and
proper electrode size.
Apart from that it can be repaired by either grinding back the weld on each side up to base metal and opting for re-welding.
Welding Defects Misalignment
Misalignment is the type of welding defect that comes under the geometric imperfections attained in the process of welding.
It is essential to acquire a stable setup that provides a useful work area, the absence of which causes setup or fitting problems.
This also occurs when we try to join metals with different thickness.
Some of the main reasons for this are,
the setup or fitting problem and also the
thickness of metals available for welding.
It can be prevented by keeping a tab on the setup process and fitting of the metals.
Welding Defects Overlap
This defect is just a protrusion of weld material beneath the weld root or weld toe. Additionally, it is the excessive flow of weld metals.
The predominant reason for this defect is improper welding techniques.
The overlap can be prevented with the help of the following,
Attaining an improvement in welding techniques.
When it comes to repairing the defect, the grinding process can help in best possible ways.
It removes the excess weld metal and the base metal can be attained through surface grinding.
Check out this nice video from weld.com!
Welding Defects Cracking
Cracks in welding are one of the most dangerous defects that can cause a lot of damage.
This damage can be lethal when the material is in fatigue-loading conditions.
Apart from that, it has several types, and each one of them should be prevented to attain quality weld and maximum strength.
Here we are providing a brief description for each one of them:
These are the type of cracks that occur due to the metal hardness problem. It usually runs along the weld direction.
Causesof Longitudinal crack
The main reasoning behind the occurrence of this problem is,
Uneven cooling of the welded part as the weld materials get cooled at different rates.
There are some other reasons also that generated longitudinal cracks such as,
wider weld bead, and
root gap is too large,
high current or welding speed and
the shrinkage stress in those areas which are under high constraint.
Remediesof Longitudinal crack
This can be prevented with the help of
A proper selection of welding consumables,
Attaining pre-heat process that helps in even cooling of the welded part and welding towards the area which has less constraint.
Apart from this, it can be repaired by re-welding after cutting the cracked part or by grinding out.
Shrinkage stress is the main problem behind the cracks. This defect is a crack that occurs at the toe of the weld.
In this, the base metal seems to have cracked.
It signifies the brittleness of the material in the HAZ area.
Causesof Transverse Crack
It is caused due to the transverse shrinkage stresses along the weld.
Remediesof Transverse Crack
It can be prevented by using a comparatively ductile filler material or by attaining a pre-heating process.
Metals become brittle while welding and this is the primary cause for under bead cracks.
Specifically, under bead cracks are the type of cracks in the melted metal of the HAZ area.
Hydrogen embrittlement is the primary carrier that causes this kind of cracks.
This can be found with the help of a non-destructive test (NDT).
Causesof Underbead Cracks
It occurs due specifically due to the hydrogen exposure on the parent metal in the heat-affected zone.
Remediesof Underbead Cracks
It can be prevented by using those electrodes, which are hydrogen controlled.
Preheating also helps in controlling under bead cracks.
It can be repaired with the help of grinding out and re-welding.
Cold cracking is among the defects that are generated when the welded metal gets a chance to solidify.
Causesof Cold Cracking
The main reasons behind this defect are,
highly restrained welds and
uneven material fitting.
Remediesof Cold Cracking
This can be prevented by welding towards areas that are smooth and consist of minimal constraints such as breakage, openings etc.
When it comes to repairing this defect, the welded part should be removed and re-welded.
Crackings are the defect that can be repaired with the help of grinding or by welding the cracks. The welding of cracks is a cumbersome process that should be attained by welding on the heat-affected zone of base metal.
The above are the types of cracks that should be prevented at any cost.
Welding Defects Spatter
Spatter is the redundant defects that are nothing but the metal drops scattered from the weld. It sticks to the surrounding surfaces.
This is one of the most common types of defects when it comes to welding.
It occurs due to,
the poor welding techniques and
improper welding parameters.
Spatter can be diminished by;
Attaining the proper welding conditions.
It can be repaired with the help of grinding or surface finishing.
Welding Defects Incomplete Fusion/Penetration
Penetration is one of the most critical aspects of welding defects. It is also known as incomplete fusion.
It is among the lethal defects that are way difficult to detect, and the evaluation of the same is complex.
This can be dangerous as it effectively hunts down the weld quality and enables the welded part to fail.
Causesof Incomplete Fusion/Penetration
It occurs when there is the absence of cohesive bond of the weld metal to the base metal or the shallow depth attained by the weld metal into the base metal.
This results in minimal throat thickness.
Apart from this, different things act as a catalyst for this defect to emerge such as shirt arc length, minimal pre-heating, fast welding speed, low current, minimal electrode size and the unavailability of the arc in the centre of the seam.
Remediesof Incomplete Fusion/Penetration
It can only be repaired, as the process of detecting is very complicated.
It can be repaired with the help of grinding the area which has penetration or incomplete fusion and opting re-welding.
Welding Defects Distortion
Distortion, as the name suggests, is the change of shape after welding. When two plates are welded, after completion, the size of the plates or the position may change which creates distortion.
Causes of Distortion:
Unequal temperature gradient present.
Large number of weld pass.
Incorrect welding technique as well as sequence.
Very slow arc travel speed.
High residual stresses in the plate.
Remedies of Distortion:
Suitable welding technique based on the metal.
Nos. of weld pass should be optimized.
Optimize the welding time duration.
Proper electrode selection.
Welding Defects Insufficient Reinforcement
Insufficient reinforcement is another type of welding defect which we see in many projects.
Reinforcement in welding means sufficient weld metals decomposition in the joint, especially in fillet or groove welding. Now, insufficient reinforcement welding means the weld metals in the joint are insufficient than required.
Causesof Insufficient Reinforcement
Fast welding process
Moving heat source very fast
Remediesof Insufficient Reinforcement
Apply slow and steady welding process
Employ skilled welder
Move heat source slow
Welding Defects Misalignment in Weld Bead
Many times, weld bead means the decomposition of filler metals into the joint, maybe alignment improperly. This misalignment incurs another welding defect.
It becomes wavy or curvy.
Causesof Misalignment in Weld Bead
Fast welding process
Weld wire not kept properly
Weld wire is not in line with weld line
Weld current and the supply of weld wire is not inline
Remediesof Misalignment in Weld Bead
Apply slow and steady welding process
Employ skilled welder
Weld wire should be in line with weld line
Weld current and the supply of weld wire should be inline
Arc Strike Type Welding Defects
As the name suggests, arc strike means another welding defect that is created by arc by mistake.
In case, the welder wrongly strikes the workpiece with an electrode on the unwanted area which causes an unwanted arc.
Causesof Arc Strike
Workpiece is not properly clamped.
Not easy access to the joint
Electrode holder was not properly layed and coating was not proper.
Remediesof Arc Strike
Employ skilled welder
Workpiece should be properly clamped.
Easy access should be provided to the joint
Electrode holder needs to be checked.
Remaining Groove Type Welding Defect
The remaining groove, as the name suggests, means that the remaining portion of the groove is missed to weld.
It makes a gap between bead to start point as well as a bead to the endpoint. This remaining groove welding defect can occur in the middle as well.
Causes of Remaining Groove
If it’s operated by robot, then there may be a problem of controlling the robot
Problem is supplying weld wire.
Insufficient supply of gas for arc/gas welding
Remediesof Remaining Groove
No interruption of gas supply
No interruption of weld wire supply
Welding Defect Burn Through
Burn through is another weld defect that needs to be known. In this defect, the weld metal or the parent metals encountered some holes.
Causes of Burn Through
Large root face
Large root gap
Welding current is very high
Remedies of Burn Through
Maintain a proper root face
Maintain proper root gap
Competent and experienced welder
Maintain proper/suitable welding current
Welding travel speed should not be slow.
Further welding can help to remove this welding defects.
Codes & Standards
Welding is a very critical subject and all types of welding defects shall be corrected or avoided to avert large accidents. Hence, it is mandatory to consider all applicable codes and standards in all applications.
The common standards are used for the welding process are as follows,
BS EN ISO 5817,
BS EN ISO 6520-1,
BS EN ISO 10042
These standards have captured all limitations or acceptable limits of welding.
Other Welding defects
We have learned many common welding defects, however, few additional defects are captured, for example:
Excess weld Metal
Chipping Mark, etc.
Here, we have considered different types of welding defects with the proper measures to combat them. Some are geometric abnormalities, while others are expected depositions.
There are some of the lethal welding defects that are capable of massively affecting longevity and weld performance.
To combat these, we need to detect these defects. Early detection of these defects is mandatory to attain the desired weld as per the designed purpose.
Repairing of defects is also necessary as there are some of the lethal ones who question the structural integrity of the structure.
Welding is a process that cannot provide cent percent perfect weld as attaining that will be time-consuming as well as costly. It is merely within the working limits that follow the specification of quality control code.