What are welding defects?
Welding defects are irregularities or unwanted occurrences on a weld joint due to incorrect welding patterns or wrong welding processes. defects may occur in welding either inside or outside of the weld metal. These defects are of different types which brought about the study so that it can be prevented.
Today I will enlighten you on the various types of welding defects, their causes, and remedies. I am huge you concentrate to fully attain the knowledge.
The various types of welding defects can be classified as external and internal defects. As the name implies, the defects that occur inside the weld are known as internal defects. while, the one that happens on the surface of the weld, which can be seen are known as external welding defects.
Internal welding defects
The following explained below are the types of welding defect that occurs inside the weld:
1. Slag inclusion: the occurrence of this defect affects the toughness and metal weldability of the material. It also decreases the structural performance of the weld material. Slags are formed on the surface of the weld. It is caused if the density of the welding current is very small, as the required amount of heat is not obtained for melting the metal surface. It can also be caused if the edge of the weld surface is properly cleaned and if the welding speed is too fast. Slag defects will occur if a proper welding angle is not used and improper travel rate of the rod is.
The remedies for slag inclusion are by increasing the current density and by cleaning the weld edges. The previous slag on the weld layer should be removed and have a proper electrode angle and travel rate. Finally, the welding speed is adjusted so that the slag and weld pool do not mix with each other.
2. Incomplete fusion: these types of external welding defects occurs when the welder does not perform the weld accurately. This causes the metal to pre-solidifies, leading to the unfilled gap. It is caused when the weld pool is very large and runs ahead of the arc due to low heat input. Incomplete fusion also occurs when the angle of the joint is too low and improper bead position. It also occurs due to an incorrect electrode and the torch angle.
Remedies for incomplete fusion are to reduce the deposition rate, increase the welding current and decrease the travel speed. Increasing the joint angle and positioning the bead properly can also prevent incomplete fusion.
3. Necklace cracking: necklace cracking occurs on electron beam welding where the weld does not penetrate properly. Where the molten metal does not flow into the cavity. it occurs when improper welding technique is implied and when using high-speed of electron beam welding. Necklace cracking often occurs in materials such as nickel-base alloys, stainless steel, carbon steel, and tin alloys.
Necklace cracking can be prevented by using the proper welding technique and using constant speed during the welding process. it can also be prevented by using proper materials for welding.
4. Incompletely filled grooves or incomplete penetration: these types of external welding defects occur only in butt welds where the groove of the metal is not filled completely. Incomplete penetration occurs due to the less deposition of the weld metal and when Improper welding technique is implied. It can also occur when the improper size of the electrode is used.
The remedy for the incomplete filled groove is by using the proper size of the electrode and using the proper welding technique. It can also be prevented by more deposition of the weld metal.
External welding defects
The following explained below are the various types of external welding defects:
1. Weld crack: this defect should be prevented at all costs as it can be presented on the surface, inside the weld material, or at the heat-affected zones. Weld crack occurs at different temperatures such as hot crack and cold crack. The hot cracks are more prominent during the crystallization of weld joints, as the temperature can rise more than 10,000 degrees Celsius. While the cold cracks occur at the end of the welding process at a low temperature. The cold cracks are visible several hours after the welding is done or even days.
Crack defects can be caused by various conditions which include:
- The presence of residual stress on the welded metal.
- Poor ductility of the base metal
- When hydrogen is used as shielding gas when welding ferrous metal
- The rigidity of the joint can cause it difficult to expand or contract the metals
- Finally, if there is high content of sulfur and carbon on the weld may cause cracks to appear.
The remedy for weld crack defects is by using the appropriate materials to prevent the chances of cracking. The gap between the weld joints should be reduced by using reasonable weld joints. Crack defects can also be prevented by preheating of the weld joints and reducing the cooling speed of the joint.
2. Undercut: undercut defect is when the part of the base metal melts away from the weld zone, which forms a groove in the shape of a notch. This reduces the fatigue strength of the joint.
Undercut welding defects are caused when the arc voltage is very high and if the wrong electrode is used. This defect can also occur if the angle of the electrode is wrong or if a large electrode is used. High electrode speed can also cause this defect.
The remedies for undercut welding defects by reducing the arc length or by reducing the arc voltage. The diameter of the electrode should be small and reduce the travel speed of the electrode. It can also be prevented by keeping the electrode angle from 30 to 45 degrees.
3. Spatter: spatter is the small metal drops deposited from the weld to the surface of welded metal. This is caused when the welding current is too high and the incorrect polarity. Improper shielded gas can also cause spatter welding defects when the arc is longer.
Spatter can be prevented by reducing the arc length and the welding current. It can also be prevented by increasing the plate angle and using the proper shielding gas. One distinct remedy for spatter is by using the right polarity, according to the condition of the welding.
4. Porosity: porosity defects occurs as gas or small bubbles gets trapped in the welded zone. It can be because when the electrode is not properly coated and when the base metal is rust or oil on its surface. This defect is also caused when the arc is longer and when the welding current is high.
The remedy for porosity defects is by selecting the proper electrode and decreasing the welding current. It can also be prevented by using a smaller arc and by slowing the process to allow the gases to escape. Finally, by cleaning oil or removing rust from the surface of the base metal.
5. Overlap: overlapping occurs when the weld face extends beyond the weld toe, which causes the metal to roll and form an angle less than 90 degrees. This defect is caused when improper welding techniques are implied and when the welding current is high. It can also be caused when a large electrode is used.
The remedies for overlap welding defects are by using proper welding technique, less welding current, and using a small electrode.
6. Crater: it occurs when the crater is not filled before the arc is broken. The outer edges cool faster than the crater causing stress and then forming a crack. Crater defect is caused when a large electrode is used, an incorrect torch angle, and an Improper welding technique.
The crater is prevented by using a proper welding technique, using a small electrode, and using a proper torch angle to reduce the stress on the metal.
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