Repair Welds

1. Mark/locate weld defects and Remove defects

Weld Crack

•The most serious type of welding defect is a weld crack and it’s not accepted almost by all standards in the industry. It can appear on the surface, in the weld metal or the area affected by the intense heat.

There are different types of cracks, depending on the temperature at which they occur:

•Hot cracks. These can occur during the welding process or during the crystallization process of the weld joint. The temperature at this point can rise over 10,000C.

•Cold cracks. These cracks appear after the weld has been completed and the temperature of the metal has gone down. They can form hours or even days after welding. It mostly happens when welding steel. The cause of this defect is usually deformities in the structure of steel.

•Crater cracks. These occur at the end of the welding process before the operator finishes a pass on the weld joint. They usually form near the end of the weld. When the weld pool cools and solidifies, it needs to have enough volume to overcome shrinkage of the weld metal. Otherwise, it will form a crater crack.

Causes of cracks

•Use of hydrogen when welding ferrous metals.

•Residual stress caused by the solidification shrinkage.

•Base metal contamination.

•High welding speed but low current.

•No preheat before starting welding.

•Poor joint design.

•A high content of sulfur and carbon in the metal.

Remedies

•Preheat the metal as required.

•Provide proper cooling of the weld area.

•Use proper joint design.

•Remove impurities.

•Use appropriate metal.

•Make sure to weld a sufficient sectional area.

•Use proper welding speed and amperage current.

•To prevent crater cracks make sure that the crater is properly filled

Porosity

•Porosity occurs as a result of weld metal contamination. The trapped gases create a bubble-filled weld that becomes weak and can with time collapse.

Causes of porosity:

•Inadequate electrode deoxidant.

•Using a longer arc.

•The presence of moisture.

•Improper gas shield.

•Incorrect surface treatment.

•Use of too high gas flow.

•Contaminated surface.

Presence of rust, paint, grease or oil

Remedies

•Clean the materials before you begin welding.

•Use dry electrodes and materials.

•Use correct arc distance.

•Check the gas flow meter and make sure that it’s optimized as required with proper with pressure and flow settings.

•Reduce arc travel speed, which will allow the gases to escape.

•Use the right electrodes.

•Use a proper weld technique.

Undercut

•This welding imperfection is the groove formation at the weld toe, reducing the cross-sectional thickness of the base metal. The result is the weakened weld and workpiece.

Causes:

•Too high weld current.

•Too fast weld speed.

•The use of an incorrect angle, which will direct more heat to free edges.

•The electrode is too large.

•Incorrect usage of gas shielding.

•Incorrect filler metal.

•Poor weld technique.

Remedies

•Use proper electrode angle.

•Reduce the arc length.

•Reduce the electrode’s travel speed, but it also shouldn’t be too slow.

•Choose shielding gas with the correct composition for the material type you’ll be welding.

•Use of proper electrode angle, with more heat directed towards thicker components.

•Use of proper current, reducing it when approaching thinner areas and free edges.

•Choose a correct welding technique that doesn’t involve excessive weaving.

Use the multi-pass technique

Incomplete Fusion

•This type of welding defect occurs when there’s a lack of proper fusion between the base metal and the weld metal. It can also appear between adjoining weld beads. This creates a gap in the joint that is not filled with molten metal.

Causes:

•Low heat input.

•Surface contamination.

•Electrode angle is incorrect.

•The electrode diameter is incorrect for the material thickness you’re welding.

•Travel speed is too fast.

•The weld pool is too large and it runs ahead of the arc.

Remedies

•Use a sufficiently high welding current with the appropriate arc voltage.

•Before you begin welding, clean the metal.

•Avoid molten pool from flooding the arc.

•Use correct electrode diameter and angle.

•Reduce deposition rate.

Incomplete Penetration

•Incomplete penetration occurs when the groove of the metal is not filled completely, meaning the weld metal doesn’t fully extend through the joint thickness.

Causes:

•There was too much space between the metal you’re welding together.

•You’re moving the bead too quickly, which doesn’t allow enough metal to be deposited in the joint.

•You’re using a too low amperage setting, which results in the current not being strong enough to properly melt the metal.

•Large electrode diameter.

•Misalignment.

•Improper joint.

Remedies

•Use proper joint geometry.

•Use a properly sized electrode.

•Reduce arc travel speed.

•Choose proper welding current.

•Check for proper alignment.

Slag Inclusion

•Slag inclusion is one of the welding defects that are usually easily visible in the weld. Slag is a vitreous material that occurs as a byproduct of stick welding, flux-cored arc welding and submerged arc welding. Is can occur when the flux, which is the solid shielding material used when welding, melts in the weld or on the surface of the weld zone.

Causes

•Improper cleaning.

•The weld speed is too fast.

•Not cleaning the weld pass before starting a new one.

•Incorrect welding angle.

•The weld pool cools down too fast.

•Welding current is too low.

Remedies

•Increase current density.

•Reduce rapid cooling.

•Adjust the electrode angle.

•Remove any slag from the previous bead.

•Adjust the welding speed.

Spatter

•Spatter occurs when small particles from the weld attach themselves to the surrounding surface. It’s an especially common occurrence in gas metal arc welding. No matter how hard you try, it can’t be completely eliminated. However, there are a few ways you can keep it to a minimum.

Causes

•The running amperage is too high.

•Voltage setting is too low.

•The work angle of the electrode is too steep.

•The surface is contaminated.

•The arc is too long.

•Incorrect polarity.

•Erratic wire feeding.

Remedies

•Clean surfaces prior to welding.

•Reduce the arc length.

•Adjust the weld current.

•Increase the electrode angle.

•Use proper polarity.

•Make sure you don’t have any feeding issues

Perform re-welding

• Repair welding is an essential process in fabrication of some structures. Properly repaired structures may have equivalent static strength, ductility, fracture toughness and fatigue strength levels as the base structures. Repair welding can be carried out as a logical procedure that ensures the production of a usable and safe component, or it can be approached haphazardly. The latter approach results in poor-quality workmanship and can lead to failed parts, large warranty claims and dissatisfied customers.

The logical sequence of successful repair welding is as follows:

•Welding procedure: the welding procedure must be accessible to the use of the welders. It must include the process that is used and specific information concerning the welding joint technique required.

•Welding equipment: sufficient welding equipment should be supplied, then delays will not occur. Standby equipment may also be required. This not only comprises welding equipment, but also includes sufficient holders, grinders, wire feeders if required, cables, etc.

•Materials: sufficient materials must be accessible to the entire job. This includes the filler metals, which should be stored properly for use on the repair. It also includes materials such as insert pieces, reinforcing pieces, etc. Materials also include fuel for maintaining preheat and interpass temperature, shielding gases if used, and fuel for engine powered welding machines

•Alignment markers: before weld making, alignment markers are occasionally employed. These can be nothing more than centre punch marks made across the joint at various locations.

•Welding Sequences: the welding sequence should be well described in the welding procedure.

•Safety: ultimately, safety cannot be overlooked throughout the welding operation. For instance, when fuel gases are used for preheating, etc., ventilation must be provided

• Weld quality: the quality of the weld must be constantly checked. The final weld should be smooth and there should be no notches and reinforcing. In order to use it, it should flowed smoothly throughout the existing structure. In fact, grinding should be done to maintain smooth flowing contours

•Repair welding can be in one of three general categories:

•Repair of weld defects;

•Repair of failed parts

•Repair of worn parts