15 Common Welding Defects You Should Know

In the discipline of engineering the existence of defects is not only accepted, it is anticipated and understood as part of the engineering science and profession. This is where the application of tolerance, or acceptable limits, comes into play.

Tolerance represents the level of acceptability of departing from perfection in engineering. Tolerance is neither uniform nor absolute; instead, tolerances are linked to the particular material, process, and applications of the relevant circumstances and nature of the structure.

When referring to defects, we are talking about the deviations from the intended design of the structure. While imperfections in design (for example, a concrete block wall that was not constructed exactly level, aligned, or uniform) are not preventable in engineering, it is our responsibility to differentiate a defect from an error.

Most defects deviate enough to be visible but are within acceptable tolerances associated with the engineering standards.

This paper will focus on industrial deviations associated with welded joints, while presenting a slightly philosophical viewpoint concerning the perception, recognition, and explanation of welded constancy or imperfections relative to engineering tolerances.

What are Welding Defects?

Welding defects refer to flaws or irregularities in a weld. It can be caused by improper techniques, insufficient procedures, or poor conditions of welding.

These defects can lead to changes in the overall appearance, strength, and reliability of a weld, and usually present differences in size, shape, or quality of the bead than what was originally intended.

In other words, a defect is anything that detracts the performance or integrity of the weld. Simply stated, defects can exist when there’s a difference between the actual outcome of a weld and the technical or design specifications of the weld.

Defects can appear at any stage in the welding process and usually fall into two categories: internal defects, and external defects. Internal defects are issues that lay below the surface and are not visible to the naked eye.

Common examples could include things like slag inclusion, incomplete fusion, or incomplete penetration – defects that will compromise the weld strength from the inside.

Conversely, external defects would include issues that are observable on the surface making inspection easier. These include defects like cracks, undercuts, porosity (small holes formed by popped gas bubbles), spatter, and overlaps.

To provide a better understanding for subsequent sections let us look at some of the common observable defects.

What are weld discontinuities?

A discontinuity is a break or disruption in the normal physical structure of a material that causes a significant change in its properties.

It is not safe to assume that all small changes in properties of a material indicate a discontinuity; only the changes that can produce a significant effect and abrupt change. These features are only welding defects if they are not within existing tolerances.

In practical terms, this means a weld that has some type of crack might be acceptable for one application but could be non-conforming for another, depending on the criteria that were established or the performance needed.

What are common weld defects?

Among the discontinuities related to the welding process, one can mention 15 types:

• Cracks
• Undercut
• Porosity
• Spatter
• Overlap
• Slag Inclusions
• Lack Of Penetration
• Incomplete Fusion
• Warpage
• Burn Through
• Wormholes
• Crater
• Lamellar Tearing
• Laminations
• Whiskers

1. Cracks

Cracking is one of the most commonly found defects in welding, and arguably the most critical. In fact, the presence of even one crack suggests that the weld will not be of quality.

These defects result from localized rupture as a result of stress and cooling in the course of, or after, the welding process.

Cracks are especially concerning because of their geometry; the sharp tips concentrate stress and greatly increase the likelihood of fracture in the weldment. In other words, a small crack can compromise the integrity of the entire structure.

Welding cracks can be a variety of sizes, shapes, and types. Types include the following:

• Longitudinal
• Transverse
• Crater
• Radiating
• Branching

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

• Hot Cracking: Hot cracking generally occurs while welding, especially if high temperatures are involved, often exceeding 10,000°C (18,032°F). The heat created during the welding process can cause a significant amount of internal stresses to develop in the weld material, especially during the crystallization phase, when the molten weld metal begins to solidify. Hot cracks typically occur when cooling is not controlled enough, or based on material properties, can not accommodate the thermal load of the weld zone.
• Cold Cracking: Unlike hot cracks, cold cracks will not show up at the time of welding. Cold cracks can often occur hours and even days after solidification, most often in welded steel during the cooling phase to solidification. Cold cracking is the result of residual stress or deformation in the metal. Cold cracking can be problematic as it can go undetected for an extended time after the welding process is completed.
• Crater Cracks: Crater cracks typically form at the very end of the welding process, just before the welder finishes a pass onto the weld joint. The formation of crater cracks mainly occurs during the last second of welding, as the weld pool is cooling and solidifying. If too little molten metal is left behind to compensate for the shrinkage occurring while the rod or wire distance was growing, a small crater crack, albeit a bond cracking defect, can occur at the end of the weld.

Causes For Cracks:

• Hydrogen is commonly present during the welding of ferrous metals. When uncontrolled, hydrogen can produce issues.
• As metal cools, it typically shrinks upon solidification and develops residual stresses.
• Contamination of the base metal can substantially influence the quality of the weld.
• Welding fast at low current can produce welds of poor quality or incomplete penetration.
• Defects and stress can arise from lack of a heat treatment or proper preheating before welding.
• Joints of poor design or improper geometry can impart stress to the weld and fabricate weak structural joints.
• High levels of sulfur and carbon within metal can diminish integrity of the weld, elevating risk of cracking.

Remedies For Cracks:

• If the material or process you are working with requires the use of preheated metal, make sure to preheat at the beginning of the welding process; this will help alleviate thermal stresses and lower the risk of cracking.
• In the course of the welding and then after welding, the heat affected area should be adequately cooled. Control and predictability of the cooling process are important to maintain the integrity of the weld and to ensure there are not any defects.
• Be aware of the joint design. A proper joint design can enhance strength and lower the risk of welding defects in the piece.
• Prior to welding, all impurities, such as rust, oil, or dirt, should be removed from the metal’s surface. Overall, cleaner material will lead to better fusion and lessen the risk of defects being introduced.
• The metal used should be appropriate for the welding process being applied. If the base and filler materials are not compatible, you may not obtain strong welds as a result. Durability and strength of a welded joint is a requirement.
• Check that the weld is large enough in size. If a weld is undersized, it may not produce enough strength needed in that section and fail due to applied load.
• Ensure the proper welding speed and amperage for that specific material and welding position. Both factors can influence the quality and consistency of the weld.
• In order to avoid crater cracks, the weld crater should not be left without being filled in. If the unfinished crater is filled at the end of the weld, this will help keep the weld intact and prevent failure. Doing so is a simple step that can help prevent a common and preventable flaw in welding.

2. Undercut

Undercut is a common welding defect that appears as a groove or notch along the edge of the weld joint. It is commonly the result when the base metal is melted but filler metal is not deposited as expected, leaving behind a cavity.

Undercut is a particular concern given that it can form a cavity, or depression, which reduces structural integrity. Over time the groove can lead to the initiation point for cracks, corrosion, or complete failure, especially in applications subjected to cyclic loads or repeated loading.

The danger is because an undercut runs alongside the weld, where the weld’s strength is needed most, ultimately reducing the thickness of the metal. The loss of material means the joint is prone to fatigue-related issues near the joint in the future.

There are different types of undercut defects based upon where or how they are present.

• Continuous undercut
• Inter-run undercut
• Intermediate undercut

Causes for undercut:

• Excessively high welding current, which can overheat and produce very poor quality welds.
• Welding too rapidly, preventing the metals from fusing properly.
• Wrong angle for torch or electrode which usually causes excess heat on free edges and distortion.
• Using an electrode that is too big for the job, making the weld hard to control.
• Poor shielding gas use, either type or gas flow rate, which will compromise protection of the weld.
• Wrong filler metal selection, either not matching the base metal or the application.
• Bad welding technique, including inconsistent motion and a lack of control, which usually makes defects.

Remedies for undercut:

• Maintain the correct electrode angle: In order to achieve correct penetration, you need to maintain a proper electrode angle. The angle can make a huge difference for the amount of penetration in a weld and the quality of a weld for even the smallest adjustments.
• Maintain the shortest arc length: Using short arcs is more effective because it helps with control of the overall weld process, helps with reducing spatter of the molten metal, and produces a nice weld bead, with smooth transitions.
• Maintain a constant travel speed: You will want to keep your travel speed constant, while not going too fast, but also not so slow that you burn through a thinner section or add too much heat to your weld joint. This means that you will need to find that healthy balance.
• Maintain the proper shielding gas: You need to make sure the shielding gas is right for the base material you are welding. This ensures that cleanliness of the weld is taken care of and will compensate for mixing that takes place in the arc area of the weld joint.
• Direct your heat to the thickest section: Often you will have to alter your electrode angle while welding so that a lot of the heat is being directed to the thicker portions of the weld joint. This helps to keep the thicker portions from losing energy too quickly when they join to the thinner portions and helps to create even fusion in the weld joint.
• Adjust your current settings: As you get to the thinner sections and edges that you need to weld, you should also reduce your amperage, to help keep from blowing through the thin material or warping.
• Choose the right welding method: Do not pick welding methods that will create excessive weaving to help with any inconsistencies in your overall penetration and weak points in the overall weld.
• Use a multi-pass method: When you are using welding pieces thicker than a quarter inch, you want to make sure to use a multi-pass method of welding to slowly build up the weld, so that you can have proper fusion and not overheat the base metal.

3. Porosity

In welding, porosity refers to small holes that may occur in the weld pool due to gas bubbles being trapped and/or failing to escape during the welding process.

This generally is a very common defect in welding, in particular in welding processes that use shielding gases such as in gas metal arc welding (TIG) and stick welding.

If the shielding gas is poor (e.g., ineffective shielding gas, not enough shielding ahead of the arc, excess shielding) it could contaminate the molten metal, which may also lead to defects that affect the overall structural integrity of the weld.

In some instances to porosity is somewhat more severe cases, the porosity may be larger voids referred to as blow holes and pits. Blow holes or pits are large voids that are formed when relatively large bubbles are trapped in the weld pool as it solidified.

Smaller gas molecules may also dissolve into the weld metal, making porosity acceptable, as it may somewhat reduce the pureness of the final product, resulting in a potential brittle weld.

Causes for porosity:

• Not using enough deoxidizing agent in the electrode.
• Keeping the welding arc too long during the process.
• Moisture getting into the work area or materials.
• Poor gas shielding or using the wrong shielding gas.
• Inadequate or incorrect preparation of the metal surface.
• Setting the gas flow rate too high.
• Working with materials that have a dirty or contaminated surface.
• Welding on surfaces that still have rust, paint, oil, or grease.

Remedies for porosity:

• Before commencing welding, clean all materials thoroughly – dirt, rust or oil will affect the weld quality.
• Ensure the electrodes and materials are both completely dry – moisture will contaminate the weld or introduce porosity.
• Use the proper arc distance – by keeping this as constant as possible you will have a consistent arc which produces better welds.
• Check the gas flow meter and make any adjustments to ensure the correct pressure and flow rate are set to fulfil the shielding requirements.
• Make sure your arc travel speed is a little slower – this allows the shielding gases more time to work and make their escape properly.
• Choose the right electrodes for the job – there are a number of different varieties of electrodes, and choosing the right one is essential to achieving clean, strong welds.
• Employ the proper welding technique – applying the correct technique encourages consistent welds or helps to eliminate defects.

4. Spatter

Spatter refers to small droplets of metal expelled from the welding arc during arc, tack, and gas welding processes. You may also see spatter in MIG welding, but it will not be as prevalent.

Spatter is generally seen on the base metal, which is commonly adhered along the weld bead and exposed parts of the weld joint design.

There is the potential for spatter to build up in the nozzle, and then, once dislodged from the nozzle, it may disfigure the selected weld bead.

This may not only reduce the weld quality of your work, but if spatters cause sharp edges, they may present a safety issue for the welder or anyone else handling the welded parts.

Causes for Spatter:

• The use of amperage may be greater than it needs to be for the application.
• The voltage may be lower than optimal for stable operation.
• The electrode may be held at too aggressive an angle during the work.
• the work surface maybe improperly cleaned or contaminated.
• the arch length appears to be excessive which can lead to instability.
• the welding polarity may be incorrect.
• there may be inconsistencies or deficiencies with wire feeding.

Remedies for Spatter:

• First, clean the surfaces you will be welding, removing any dirt, rust or oil because this will adversely affect the quality of your weld.
• Work with short arcs, as an excessive arc length leads to excessive spatter, penetration problems and less overall control.
• Adjust the welding current; currents too high or too low negatively affect your welds, so you should feel free to change the current according to the material you are working with and with the electrodes you are using.
• Adjust the angle of the electrodes slightly. A slight angle change towards the weld pool will allow you to control and see the weld pool better overall.
• Double check for the polarity setting. The correct polarity is necessary according to the type of electrode being used if you want a proper signed clean weld.
• Check the wire feeding. Any slip, speed inconsistency, or tangling will negatively hamper your weld and be definitely worth a minute inspection.

5. Overlap

Overlap, also known as cold lap, is a welding flaw in which the weld metal exceeds the capabilities of the joint. Instead of creating the appropriate metallurgical bond, the molten metal flows out over the surface of the base metal, particularly at the toe of the weld bead, and does not fuse to it.

Overlap usually occurs on the horizontal leg of a horizontal fillet weld, particularly when done under less than ideal conditions. It can also occur on either side of capping passes made in the flat position.

Overlap is common in gas metal arc welding (GMAW) practices when excessive electrode extension has allowed for an increase in the deposited metal while utilizing a lower power input process.

It is also the result of poor arc direction, whereas the arc is pointed too much towards the vertical leg and standing nearly straight up with the electrode.

To avoid this, the fillet weld should be a proper size, typically not larger than 3/8 inch (9.5 mm), and the arc must be controlled with good manipulation techniques throughout the weld.

Causes for overlap:

• Wrong welding techniques can contribute to defects in the final weld.
• Using unnecessarily big electrodes to do the job is also a common cause of defects in welding.
• Using too much welding current can also be a factor precipitating defects.

Remedies for overlap:

• Choose the correct welding process that is suitable for the materials and application at hand.
• Use a smaller diameter electrode to increase control and accuracy in the weld.
• Use lower welding currents to prevent excessive heat input, which results in a better quality weld.

6. Slag Inclusion

Slag is a damaging byproduct that is produced when welding in various forms of welding including shielded metal arc welding, stick welding, flux-core arc welding, and submerged arc welding.

These substances can produce what is called a slag inclusion which is essentially an impurity that may become trapped in the weld either between welding passes or at the surface at the top of the weld.

Slag typically forms when a material in flux, the solid shielding material that is used in welding, melts and bonds with the weld pool. If the slag is not handled properly and removed or the welding technique is not consistently applied, those inclusions, or impurities will fuse in the weld.

These inclusions would then have a direct impact on not only the appearance of the weld but the structural integrity of the weld too. Slag inclusions will reduce weldability and toughness in a welded joint, which would inherently reduce the performance level of the final weld.

Causes for Slag Inclusion:

• Inadequate surface preparation prior to welding.
• Welding performed at an excessively high travel speed.
• Failure to properly clean each weld pass before initiating the next.
• Use of an incorrect or inconsistent welding angle.
• Premature cooling of the weld pool, leading to potential defects.
• Application of insufficient welding current.

Remedies for Slag Inclusion:

• Increase the current density until you get better penetration.
• Prevent a rapid cool down in the weld—cracking occurs when welds cool too quickly.
• Properly set the electrode angle to keep an arc at an even distance while making the weld.
• Clean any slag from the previous bead prior to beginning the next pass; this prevents flaws.
• Adjust the speed if necessary, too fast or too slow may cause defects in the final product.

7. Lack of Penetration

Unfused root, or incomplete penetration, is a welding defect where the weld bead does not completely penetrate to the root, or other side of the workpiece. This type of discontinuity can weaken the weld and reduce the strength of the welded joint.

To fix the problem the following can be attempted to resolve the issue: increase the current, decrease the travel speed, and make a change to the geometry to create better fusion to the root.

Causes for Lack of Penetration:

• Excessive gap between the metal parts: If the distance between the parts you want to weld is too great the filler metal cannot bridge the gap, resulting in a weak joint.
• Moving the weld bead too quickly: If the weld pool moves too quickly the pool cannot form properly or deposit enough metal across the joint.
• Amperage set too low: If the amperage is not high enough, there is not enough current causing metal not to melt properly; thus, leading to weak or inconsistent welds.
• Using an electrode that is too large: A larger electrode will typically be less controllable for you and may not be the proper size or type for the weld you are doing.
• Misalignment of the metal: If the pieces are not lined up properly before welding this affects the integrity and strength of the weld.
• Improper joint preparation or design: Having the wrong preparation can create all different kinds of problems while welding, and such as lack of penetration and insufficient fusion.

Remedies for Lack of Penetration:

• Ensure the joint has the correct geometry for the type of weld you’re doing.
• Choose an electrode that’s the right size for the job; it makes a difference.
• Slow down your arc travel speed; going too fast causes problems with the weld.
• Use a welding current for that material and process.
• Check to make sure everything is lined up before you start the weld.

8. Incomplete Fusion

Incomplete fusion is where there has been a localized lack of contact between the welding metal and either the edge of the joint or the face of the other weld bead. To correct these issues, you have several options.

You can increase the welding current or slow down the travel speed to achieve a better penetration and fusing with the previously deposited weld metal. In some cases, just changing the joint design will fix the problem.

Other cases involve the use of specific procedures and techniques to eliminate the arc blow caused by magnetic forces.

Incomplete Fusion occurs with localized lack of fusion, either at the joint edge or at the face of the previously deposited strand. To correct this discontinuity, you can increase the current, decrease the welding speed, change the joint geometry or use some artifice to avoid magnetic blowing.

Causes for incomplete fusion:

• Inadequate heat input – Not enough heat can lead to inadequate fusion and weak welds.
• Contaminated surface – Dirt, oil, rust, or any other contaminating residue left on the base material can severely affect weld quality.
• Improper angle of the electrode – Holding the electrode at the wrong angle can lead both to less penetration and/or an ugly bead.
• Inappropriate diameter of the electrode – Using an electrode which was too thin or thick for the material being welded can lead to a flawed weld.
• Excessive travel speed – Travel too quickly in a welding application and the weld pool may not have adequate time to form properly, leading to weak joints.
• Oversized weld pool – If the weld pool is too large and moves ahead of the arc the welder may be unable to maintain control. As a result, a defective weld can occur.

Remedies for incomplete fusion:

• Ensure that the welding process uses sufficient welding current and has the correct arc voltage for the job so that they are balanced, which is recommended for a stable arc and appropriate penetration.
• Always make sure to clean the metal surface before welding. Any dirt, rust, or oil will negatively impact the arc stability as well as overall weld quality.
• Do not allow the molten pool to grow too large and flood the arc area, as that will not allow the welder to see or control the welds as effectively.
• The larger the electrode size and proper angle, will also affect the consistency of weld bead.
• If possible, minimize deposition rate. Slowing down will allow for better control over the process and minimize arc blow and spatter.

9. Warpage

Warpage is the undesirable distortion or deformation in one’s metal and can occur either in shape and/or alignment when fused through improper heat application in the welding process.

Warpage can occur from factors induced by thermal heat and will create non-uniform thermal expansion/contraction of the welded materials. Warpage is much more likely to happen when working with thinner plate alloys.

Thinner plates are much thinner, therefore, it factors less thermal area exposed for equal parting to occur, creating distortions on break.

Cause for Warpage:

• Disparity concerning the thermal profile in the welding sequence.
• Similar to employing a wrong sequence, whereby temperature gradients are present during welds.
• Moving the welding arc to slowly during use.
• Making multiple passes with the wrong diameter electrodes.
• Large residual stress present within the plate prior to welding.

Remedies for warpage:

• Setting the torch at the proper angle may help minimize the amount of stress placed on the area of the metal.
• Using a smaller electrode usually results in a smaller crater and a better finish.
• Using the proper welding technique is also important in obtaining better results, and minimizing the chance of potential defects.

10. Burn Through

Burn-through, or melt-through, happens when the weld arc accidentally melts all the way through the base metal and an open hole is left in the base metal. Burn-through defect is more common with thinner metals where accidental weld penetration of full thickness metal is more likely to happen.

Causes of Burn-Through:

• Welding settings that are too high for thicker metal sections.
• Excessive spacing or gaps between the metal pieces being joined.
• Moving the torch too slowly during the welding process.
• Choosing the wrong wire size for the specific welding task.

Remedies for burn-through:

• Avoid the temptation of cranking the welding current too high—a weld that is too forceful will adversely affect penetration and will produce excessive spatter.
• Try to keep the gap between the metal plates as minimal as reasonable—too many gaps will contribute an overall lower strength of the joint and create challenges to achieving a clean weld.
• Try to maintain an appropriate travel speed. Welding too slowly can cause the weld to overheat, which often leads to a poor weld bead appearance. What is an appropriate speed would depend on the welding process you are using. For MIG welding, trying to achieve a travel speed between 14 to 19 inches per minute (IPM) would be best. With an orbital type of welding, slow the speeds to around 4 to 10 IPM would achieve the best results.
• Try to avoid using wide bevel angles. It is not that you cannot use wide bevel angles, but they typically will have you adding more weld than is needed, which creates confusion.
• Stick to lighter gauge wire sizes when you feel comfortable—lighter wire feeds well and usually allow for better control and cleaner results.
• Make sure to keep things tight and clamped down when welding so the metal pieces do not move the whole time.

11. Wormholes

Wormholes essentially represent narrow, tube-shaped voids which form in a casting that contain excess trapped gas. Their shapes may vary circular or elongated depending on their orientation.

On Radiographic Testing (RT), wormholes usually show up as sharply defined dark outlines, so are usually easily identifiable.

The methods of prevention for wormholes are quite similar to the methods applied in the control of porosity. In both cases, reducing gas entrapment during the casting process is critical for the avoidance of defects.

12. Crater

Craters are a specific defect in welding that typically occur right before the end of a weld joint. Craters in a weld are usually the result of not filling the molten weld pool with fill material, prior to extinguishing the arc.

When this occurs, the outer edges of the weld often cool and solidify quicker than the center, creating an uneven thermal contraction. If not enough filler metal is added to account for the shrinkage, internal stress builds, resulting in a crater crack.

Causes of Crater:

• Inadequate filling of the weld crater
• Misalignment or improper angling of the welding torch
• Selection of an unsuitable welding technique

Remedies for Crater:

• Make sure that the crater is properly filled to avoid defects or weak areas.
• Keep torch at an appropriate angle to avoid stress on the base metal surface.
• Use a smaller electrode to allow better control when welding.
• Use the right welding process to match your material and the job requirements.

13. Lamellar Tearing

Lamellar tearing is a type of welding defect generally found near the bottom (or in the bottom of a pass) of the welded rolled steel plates. The unique nature of lamellar tearing is its appearance as a terraced or step like crack formation.

Lamellar tearing generally occurs due to thermal contraction within the steel during the cooling process of welding. Lamellar tearing can occur due to thermal contraction and can occur outside the heat affected zone, usually oriented parallel to the weld fusion lines and heat affected zone.

Causes of Lamellar Tearing:

• Ensure that the weld metal is deposited in a manner that does not disallow strong, cohesive bonding across the surface.
• Do not use the wrong material or weld in the wrong direction; the weld can be severely compromised.

Remedies for Lamellar Tearing:

• Welding should be done in the last stage of production to preserve correct alignment and reduce distortion risk. 
• Selecting quality materials and using the right welding direction will ensure strength, endurance, and involve positional accuracy with the end product.

14. Laminations

Laminated has layers of weakness or separation, that typically run parallel to the surfaces of the metal after it had been worked, and is a type of metal defect.

Laminated is not the same as lamellar tearing; lamination is generally more widespread, and laminated can have thicker layers of non metallic material in the metal.

The defects typically originate from defects such as seams, blisters, inclusions, pipe, or segregation, which are drawn out and aligned when the metal is worked.

An issue with lamination type issues, especially in welding capabilities, is they are not always easy to recognize through simple visual inspection.

Nonetheless, the implications of these defects can be serious to the performance of the component as a whole when these defects cover a large enough area by affecting the structural integrity of the material; that affect can display itself by inducing local buckling, or failure of welded components.

15. Whiskers

Whisker defects are a typical phenomenon in MIG welding where short bits of electrode wire project from the root side of the weld joint. This usually happens when the electrode wire is allowed to protrude from the front edge of the weld pool during the welding process.

Whiskers impact the look of the weld and can compromise the overall strength of the weld.

For many applications, whiskers are ultimately unwanted inclusions in the weld and can affect the structural integrity of the weld joint. In piping applications, they can impact fluid flow in the piping system and potentially cause damage to equipment if not corrected.

How to Detect Welding Defects

Methods of testing are crucial in identifying whether welds have been completed to required specifications. Testing determines not only the size and nature of defects but also causes and possible remedies.

Testing can be time consuming and take time, but it will assist and serve the structural integrity and safety of welded joints.

There are two standard procedures for finding defects in a weld metal:

Non-Destructive Testing

Non-destructive testing (NDT) provides an effective means of locating defects or discontinuities in welds without causing damage the material being examined.

NDT means of testing is valuable in fast-paced production environments where testing isn’t possible for every single item and instead, it is acceptable to take a representative sample from the total batch.

There are several ways non-destructive testing and evaluation can be conducted. Normally, a number of the following methods are typically included: visual inspection (VI), liquid penetrant testing (PT), magnetic particle testing (MT), eddy current testing (ET), ultrasonic testing (UT), acoustic depending on the specific material and defect being explored.

Destructive Testing

Under destructive testing, you intentionally overload completed welds or component until it fails, either to collect important performance data.

This method is extremely useful in determining the limits of the structure of the material or joint. In many cases, destructive testing helps to enhance non-destructive testing, especially when the goal is to substantially reduce weld defects in the production stage.

The most common destructive tests used in the evaluation of the strength and performance of weld metal include acid etching, guided bend tests, free bend and back bend tests, nick breaks, and tensile strength testing. These techniques can expose deficiencies that may not be visible with just visual inspection.

How to Distinguish Between Weld Discontinuity and Weld Defects

Welding discontinuities, are interruptions that break the homogeneous nature of the weldment. Discontinuities can be in the base (parent) metal or in the weld metal. Discontinuities often arise from inadequate welding techniques, improper welding patterns, or poor planning.

Usually, these discontinuities are not as large, or shaped as intended, and not as quality of the weld bead overall, depending on the situation it may or may not be apparent on the surface.

Discontinuities are not to be confused with welding defects. Defects and discontinuities are not the same. They differ in the following way:

• Welds are considered a defect only when they are deemed not to be up to the quality control team’s standards, and subsequently rejected.
• Although discontinuities may remain in service after passing field tests, defects are treated much more seriously and generally cannot be left in place, regardless of their nomenclature.
• For the most part, discontinuities are compared against a pre-established set of acceptable limits; if the discontinuity falls inside of these limits, then the weld may still be allowed.
• Minor weld discontinuities are generally considered “part of the normal variation” in manufacturing and tolerable, whereas anything labeled as a defect must be repaired or removed.

If discontinuities exceed the defined acceptable limits of a project, they will be determined to be weld defects.

It is critical to understand the difference as it relates to the structural integrity and safety of the product. With that said, there is an inherent need to regularly inspect welding operations in a safe and efficient manner in order to provide the quality and compliance required.

FAQs

Sources:

• https://slv.co.id/7-common-welding-defects-causes-remedies/
• https://allgas.us/b/what-are-welding-defects–types-causes-and-remedies
• https://technoweld.com.au/2019/11/13/the-most-common-welding-defects-causes-and-remedies/