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Welding defects are generated in a welding job due to the faulty or poor technique used by the inexperienced or unskilled welder or due to fundamental difficulties in the welding operation.
An ideal weld or good weld should be such that adequate fusion exists between the filler metal and edge preparation together with good penetration.
Types of welding defects:
- External defects (Defects occur upper surface of the welded work)
- Internal defects (Defects occur under the surface of the welded work)
In External defects there are various defects which are:
- Incorrect profile ( Welding is not done properly)
- Crater ( A large Cavity occurs where electrode sparks continuous on a single point )
- Spatter and surface porosity ( On the welded parts there some drops occurs )
- Incomplete filled groove (Not filled completely )
- Distortion (This occurs were not welded properly )
Whereas In Internal defects there are various defects which are:
- Blow holes and internal porosity
- Lack of fusion
- Incomplete fusion
1. Incomplete Penetration:
Incomplete penetration occurs when the Depth of the welded joint is insufficient.
penetration is defined as the distance from the base plate top surface to the maximum extent of the weld nugget.
- Improper joints
- Too large root face, root gape, and bevel gear.
- Wrong hold position of the electrode
- Too large electrode diameter and longer arc length
- Less arc current and faster arc travel speed
- Incorrect polarity while welding with DC.
- Increasing the heat input.
- Reducing travel speed during welding.
- Ensuring that the surface to be joint fit properly
- Changing the joint design.
This is may be in the form of slag or any other foreign material, which does not get a chance to float on the surface of the solidifying weld metal and thus gets entrapped inside the same.
Inclusion lowers the strength of the joint and makes it weaker.
- Too high or too low arc current
- Long arc and too large electrode diameter
- The too small included angle of the joint
- Insufficient chipping and cleaning of previous passes in multipass welding.
- Wrongly placed tack welds.
- Cleaning the weld bed surface before the next layer is deposited, by means of a wire brush.
- Providing sufficient shielding gases.
- Redesigning the joint so as to permit sufficient space for proper manipulation of the puddle of molten weld metals.
3. Porosity and Blowholes:
Porosity is a group of small voids and blowholes are comparatively bigger isolated holes or cavities.
They are mainly generated due to entrapped gases.
- Use of improper electrode and longer arc
- faster arc travel speed.
- Too low and too high arc currents
- Due to gas entrapment during solidification of the weld
- Unclean job surface i.e. presence of scales, rust, oil, and grease, etc on the surface of the job.
- Proper selection of electrode and filler materials.
- Improve welding technique such as preheating of the weld area or an increase in the rate of heat input.
- Reducing welding speed to allow time for gas to escape.
- Proper cleaning and the prevention of contaminants from entering the weld zone.
Spatter is the small metal particles which are thrown out of the arc during welding and get deposited on the base metal around the weld bead along its length.
- Excessive arc current
- Use of longer arc, damp electrodes
- Electrode being coated with improper flux ingredients.
- Due to the expansion of gas bubbles entrapped in the molten globules of metal.
- Use proper arc current to weld, arc length, fresh electrodes.
- Use of AC power to reduce arc blow.
Distortion is the change in the shape and difference between the position of two plates before and after welding due to the temperature gradient present at various point along the joints.
In general, we can say that distortion is due to unequal expansion and contraction of the weld metal and all kind of distortion increase with the volume of metal deposited.
Distortion of the weldment can be divided into three types:
- Longitudinal shrinkage (Occurs Parallel to the weld lines)
- Transverse shrinkage (Perpendicular)
- Angular shrinkage (rotation around the weld lines)
- A great number of passes with small diameter electrodes
- Slow arc travel speed
- High residual stresses in the plate to be welded.
- Using improper welding sequences.
- Use the proper amount of weld metal as per the requirement of the joint. It will reduce the contraction forces.
- Use an appropriate number of weld passes.
- Place the weld near the neutral axis.
- Use proper welding sequences.
Other remedies are:
- Reduce the welding time so that too great a volume surrounding metal cannot be expanded.
- Wled the large weldments into sub-assemblies.
- Peening should be done to remove the shrinkage force during or after welding.
An undercut is a kind of weld defect which forms a groove in the parent metal along with the sides of the weld bead.
Groove reduce the thickness of the plate and also reduce the strength of the weld.
- Wrong manipulation and inclination of an electrode and excessive weaving.
- Too large electrode diameter.
- Longer arc.
- Faster arc travel speed.
- Magnetic arc blow.
- higher current.
- Use proper arc current, electrodes.
- Weaving should be proper and as per the requirement.
- Use proper arc travel speed.
7. Hot Tear:
In this welding defect, the deposited metal being hot starts developing crack from the nearby edge so that after it has been solidified the crack increase.
The hot tear is also known as solidification cracking is due to tearing of the grain boundaries of weld metal before complete solidification has taken place and metal is still in the plastic state.
- Improper selection of proper materials.
- Welding current is not proper.
- Improper electrode thickness.
- Select proper electrode material.
- Welding current should be optimum as per the requirement.
- Electrode thickness should be optimum and according to the base metal to be welded.
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