The Defects In Weldings, Which May Occur In Normal Construction, Is A Matter Of Importance For Design Engineers. A lot of Welding Defects Or Welding Discontinuity Generally Observed In Welding Joints Which Are As Follows:
Common welding defects
- Lack Of Penetration (Insufficient Or Incomplete Penetration)
- Lack Of Fusion (Incomplete Fusion)
- Inclusion(Slag inclusion,Tungsten inclusion)
- Porosity (Uniformly Scattered, Cluster, Linear, Pipe)
- Crack (Longitudinal, Transverse, Crater, Throat, Toe, Root, Under- Bead, Heat Affected Zone, Hot, Cold Or Delayed)
- Faulty Weld Size &Profile
Apart from these welding defects, there is also various kind of welding defects occurs in welding operation such as
Other welding defects
- Concavity Or Convexity
- Arc Strikes
- Excessive Reinforcement
- Improper Enforcement
- Defects In Heat Affected Zone
- Burn Through
- Surface Irregularity(Overlap)
- Tungsten Inclusion
- Arc Craters
- Lamellar Tearing
- Laminations And Delaminations
- Las And Seams
As we can see various kinds of welding defects are observed in the welding operation in which some are related to the base metal and others related to weld metals.
Description of welding defects
Lack of penetration
Lack of penetration is defined as an incomplete weld penetration in the root zone where the fusion faces of the root zone are not melted completely. It may be classified as -Incomplete penetration and Incomplete root penetration. The root cause of this defect is improper cleaning, Low welding current, fast arc travel speed, short arc length and lack of preheating in thicker metals. Prevention: This welding defect can be prevented by eliminating the above mentioned root cause.Lack of inter-run fusion
Lack of fusion
this defect occurs ,when the weld metal fails to fuse boundaries of the base metal or side wall of the base metal,
This defect can come in the side wall of the base metal or between inter pass and root area respectively callad Lack of side wall fusion, Lack of inter run fusion and Lack of root fusion.The root cause of this defect is improper cleaning, Low welding current, fast arc travel speed, short arc length and lack of preheating in thicker metals.
Prevention: This defect can be prevented by eliminating the above mentioned root cause.
Undercut generally occurs when the welding current is too high or using long arc length, this defect can come if joint is rusty also. It can be seen as some sort of grove cut in the welding toe area and left unfilled.For repair, this defect needs to clean the joint before start welding operation, control arc length and welding current. Acceptance criteria :Typically undercut has an allowable limit as per different welding codes and standards.For pipe, it should not be exceeded more than 5%of the thickness of the plate or 1/32” or around .75mm. Whatever is the minimum value is applicable.
There are two types of inclusion that occur in weld metal respectively slag inclusion and tungsten inclusion. Slag inclusion:Slag inclusion is a type of slag entrapment between weld layers or between the base metal and weld metal, especially in the multi layer welding process, but sometimes it can come in single pass welding also. Slag inclusion occurs in which the slag material is used like SMAW, SAW Tungsten inclusion: Basically tungsten inclusion occurs when tungsten touched in the molten weld pool due to the using short arc length, using small tungsten size, high current, specially in a manual welding process where tungsten is used as an electrode like GTAW. Plasma Arc.Cause: Low welding current, presence of dirt, rust, mill scale, using a damaged electrode
Prevention: This defect may be eliminated by using aproprieat welding current, proper cleaning each layer after welding is over, preheating the joint
For repair, this defect needs to remove slag with grinding thoroughly and re weld it.
This type of defect is actually local based coalescence out side of the weld area or on the base metal anywhere and may occur due to the carelessness of the welding operator or lose connection of ground point. This defect may be prevented by using a fire blanket properly, the tight connection of earth clamps and carefull welding operation.
When Arc strick occurs on the base metal, suddenly the temperature of that portion goes too high and again comes down fery fast. By this action, the microstructure of the metal of that part may be altered and can cause a brittle freture or crack.
For repair, this defect needs to grinding deep until it Is removed compleatlly, and than a weld.
Welding defects Cracks
Various type of cracks occurs in welding joint and can be caterized as :Longitudinal Transverse, Crater, Throat, Toe, Root, Under- Bead, Heat Affected Zone, Hot, Cold Or Delayed) Read More
Basically, this kind of defect occurs on the surface of weld metal or below the weld surface, when the weld surface is bellowed the adjacent surface of the base metal. due to the improper welding techniques and welding parameters. For repair, this defect needs to apply proper welding techniques and welding parameters. Simply joint should be a little bit grinding and fill it properly by the same welding process
Misalignment is basically due to joining two different or dissimilar thicknesses also this defect occurs due to carelessness, This type of defect is also called hi-low and it is difficult to repair inside of the pipe or tube. There are two types of misalignment that are as follows:
- Lenier type of misalignment
- Angular type of misalignment
For repair, this defect needs to grind the defect portion of the joint and prepare the required shape again.
Concavity Or Convexity
These kinds of defects occur when the weld metal exceeds or is insufficient to the specified allowable limit of the weld, due to welding current and travel speed.
Prevention: it can be prevented by controlling arc travel and welding current. For repair, this defect needs to grind the excess weld metal if it is in convex deformation or needs to weld more for Concave (insufficient weld metal).In the case of root concavity back welding is preferred
IS Reinforcement welding defects?
The point is notable that the reinforcement is an essential part of the welding operation due to the required strength of the welding joint. But in case of excess or less reinforcement, it will be countered as a welding defect.it can be classified as Excessive reinforcement, Insufficient reinforcement. This defect occurs due to a lake of welding current or slow arc travel.
generally, it is actable only 1/16” in pipe and 1/8” in the plate. And it can be prevented by using proper welding current and arc travel speed. For suck back or insufficient reinforcement, the allowable value is 5%of the thickness of the metal or does not exceed around .75mm, whichever is minimum should be considered. For repair, this defect needs to grind the excess weld metal. or use back weld in the case of insufficient reinforcement
Overlapping is generally due to the extends beyond the toe of the weld and it is not allowed in any amount of weld metal. It can be controlled by proper welding technique and arc travel speed.For repair, this defect needs to grind the defect portion of the joint. Burn Through
Burn through is an undesirable hole that is melted through the base metal and it can remain inside the welding joint mainly it occurs due to excessive welding current or low arc travel speed and it can be prevented by reducing the heat input .or heat synce can be used to reduce the heat input also.
Spatters are likely small particle of the weld metal that is expelled by welding activity due to high current use and longe are length. It can be prevented by using proper welding parameters. and covering through a fire blanket.
For repair, this defect needs to be clean properly using grinding or chipping operations.
The arc crater comes due to improper weld termination, where the weld pool is left incomplete due to improper weld termination techniques and can be repaired by welding, but grinding it properly if looking crack.
Discontinuities in welds
Discontinuities actually break the continuity of the weld metal with the parent metal.it may related to welding process , Metallurgical or Related to Design.
Welding discontinuities can be classified as shown here