Weld Quality Testing
To ensure the satisfactory performance of a welded structure, the quality of the welds must be determined by adequate testing procedures. Therefore, they are proof tested under conditions that are the same or more severe than those encountered by the welded structures in the field.
This page contains visual inspection tips. The following pages contain inspection methods for GMAW and physical weld testing.
These tests reveal weak or defective sections that can be corrected before the material is released for use in the field. The tests also determine the proper welding design for ordnance equipment and forestall injury and inconvenience to personnel.
NDT refers to nondestructive testing. It is an approach to testing that involves evaluating the weld without causing damage. It saves time and money including the use of remote visual inspection (RVI), x-rays, ultrasonic testing, and liquid penetration testing.
In most welds, quality is tested based on the function for which it is intended. If you are fixing a part on a machine, if the machine functions properly, then the weld is often considered correct. There are a few ways to tell if a weld is correct:
- Distribution: Weld material is distributed equally between the two materials that were joined.
- Waste: The weld is free of waste materials such as slag. The slag after cooling should peel away from the project. It should be removed easily. In MIG welding, any residue from the shielding gas should also be removed with little problem. TIG, being the cleanest process, should also be waste-free. In Tig, if you see waste, it usually means that the material being welded was not cleaned thoroughly.
- Porosity: The weld surface should not have any irregularities or any porous holes (called porosity). Holes contribute to weakness. If you see holes, it usually indicates that the base metal was dirty or had an oxide coating. If you are using MIG or Tig, porosity indicates that more shielding gas is needed when welding. Porosity in aluminum welds is a key indicator of not using enough gas.
- Tightness: If the joint is not tight, this indicates a weld problem. In oxyacetylene welding, if using autogenous welding, where there is no filler material, the weld must be tight. Same for Tig autogenous welding. The gap is not as critical in other types of welds since any gap is filled in by the filler material. That said, gaps, in general, indicate a potential quality problem.
- Leak-Proof: If you are repairing an item that contains liquid, a leak is a sure-fire way (and obvious way) to see that there is a problem. Same for something that will contain a gas. One testing method is to use soap bubbles to check for problems (can be easily applied with a squirt bottle.
- Strength: Most welds need to demonstrate the required strength. One way to ensure proper strength is to start with a filler metal and electrode rating that is higher than your strength requirement.
Other checks using visual methods include checks before (root face, gap, bevel angle, joint fit), during (electrode consumption rate, metal flow, arc sound, and light), and after welding (undercut, root fusion issue, pinholes, excessive spatter, weld dimensions).
Visual Inspection (VT)
Visual inspection is a non-destructive testing (NDT) weld quality testing process where a weld is examined with the eye to determine surface discontinuities. It is the most common method of weld quality testing.
Advantages of nondestructive weld quality testing:
- Inexpensive (usually only labor expense)
- Low-cost equipment
- No power requirement
- Quick identification of defects and downstream repair costs due to issues that weren’t caught early
- Inspector training necessary
- Good eyesight required or eyesight corrected to 20/40
- Can miss internal defects
- Report must be recorded by inspector
- Open to human error
Visual Weld Quality Testing Steps
Practice and develop procedures for consistent application of the approach
- Inspect materials before welding
- Weld quality testing when welding
- Inspection when weld is complete
- Mark problems and repair the weld
Visual Inspection During Welding
- Check electrodes for size, type and storage (low hydrogen electrodes are kept in a stabilizing oven)
- Watch root pass for susceptibility to cracking
- Inspect each weld pass. Look for undercut and required contour. Ensure the weld is cleaned properly between each pass.
- Check for craters that need to be filled
- Check weld sequence and size. Gauges are used to check size.
Inspection After Welding
- Check weld against code and standards
- Check size with gauges and prints
- Check finish and contour
- Check for cracks against standards
- Look for overlap
- Check undercut
- Determine if spatter is at acceptable levels
10 Common Welding Defects You Should Know
What are Welding Defects?
Welding Defects can be defined as the irregularities formed in the given weld metal due to wrong welding process or incorrect welding patterns, etc. The defect may differ from the desired weld bead shape, size, and intended quality.
Welding defects may occur either outside or inside the weld metal. Some of the defects may be allowed if the defects are under permissible limits but other defects such as cracks are never accepted.
Engineering has always recognized the existence of imperfections and working with tolerances. Tolerance is the term that defines the degree of acceptance before imperfection. Thus, any tolerance should only be defined for a certain application, process, and material used.
Imperfections are known as any difference regarding the project of the structure. They are inevitable in engineering, but not all of them should be treated as unacceptable.
What are weld discontinuities?
Discontinuity is an interruption in the typical physical structure of a material that sharply changes its properties. Thus, the simple variation of properties does not characterize a discontinuity. However, only discontinuities that exceed the tolerance limit should be considered as welding defects.
Thus, a weld with a particular crack can be considered approved or disapproved for different applications.
Types of Welding Defects
Now that you know how to reveal welding defects, we’re going to learn to identify what kind of weld defect we are dealing with. Each has its own characteristics and needs a different approach to repair.
- Lack Of Fusion or Incomplete Fusion
- Slag Inclusions
- Burn Through
1. Lack of Penetration or Incomplete Penetration
Incomplete Penetration occurs when the root of the weld bead does not reach the root of the joint to weld the opposite surface in the part. To correct this discontinuity, you can increase the current, decrease the welding speed, or change the joint geometry.
- 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.
- Improper joint.
- Use proper joint geometry.
- Use a properly sized electrode.
- Reduce arc travel speed.
- Choose proper welding current.
- Check for proper alignment.
2. Lack of Fusion or Incomplete Fusion
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.
- 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.
- 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 rates
It occurs with depression, like a notch, at the foot of the cord. To correct this discontinuity, you can reduce the current or reduce the welding speed.
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.
- 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.
- 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
4. Slag Inclusion
It occurs with the retention of solid materials, metallic or not, within the weld metal. Causes are inadequate cleaning of weld surface between passes. It can also occur in single-pass welds when slag gets trapped in the root and toes of the weld.
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. It 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.
- 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.
- Increase current density.
- Reduce rapid cooling.
- Adjust the electrode angle.
- Remove any slag from the previous bead.
- Adjust the welding speed.
Spatter occurs with the projection of molten particles from the weld bead. To correct this discontinuity, one can reduce the current and control the instability in the metal transfer.
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.
- 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.
- 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.
6. Weld Crack
Among the discontinuities of metallurgical origin, one can mention cracks, which may appear in the zone affected by the weld (Fused Zone or Heat Affected Zone) due to several factors, such as the contraction of the solidifying metal and the growth of grains, and can be classified as cold cracks, solidification cracks and reheating cracks.
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 in 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.
- 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.
- 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.
It occurs with the formation of gas bubbles retained within the melt zone. It can occur internally and also surfacing on the surface. To correct this discontinuity, it is possible to correct the flow of the protection gas and to use gases of better quality (with greater purity in its composition).
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.
- 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.
- 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.
Overlap occurs when the weld face extends far over the weld toe. This is mostly caused by using too large electrodes or having a bad welding technique.
- Improper welding technique.
- By using large electrodes this defect may occur.
- High welding current
- Using a proper technique for welding.
- Use small electrode.
- Less welding currents.
Warpage is an unwanted change in the shape and position of the metal parts. It happens when the heat usage is wrong and is caused by the contraction/expansion of the welded parts.
- Incorrect torch angle.
- Use of large electrode:
- Improper welding technique
- Using a proper torch angle may reduce the stress on the metal
- Using a small electrode may also decrease the crater.
- Use a proper technique.
10. Burn Through
If the weld metal penetrates the base parts, we talk about burn through. This is a common discontinuity when welding thin parts. It happens when the root opening is too large or too much voltage is used.
How to know if it’s a Weld Discontinuity or a Welding Defect
A weld discontinuity is easy to recognize because it looks like an interruption of normal flow. It is also known as a weld imperfection, and it can be found in the weld metal or the parent metal. A discontinuity happens in the weld metal due to the wrong welding pattern or welding technique. It can differ from the weld bead shape and thickness and ultimately, the quality.
In general, a discontinuity should be avoided and dealt with, but they are marginally less serious than a welding defect. Nonetheless, if you do find a weld discontinuity, you need to fix it.
That said, a group of weld discontinuities can become a weld defect, if they exceed the limits stated in your project. This goes in accordance with your country, the material, and the type of environment you are in.
Ultimately, the most effective way to inspect a welding job, especially in tight spaces, is using a welding camera. Here are some video examples of how that works.
Identifying Welding Defects Before It’s Too Late
It is impossible to overstate the importance of catching welding defects in time. Even the slightest defect can be catastrophic. From taking care of the welding technique, down to the welding current and supervision, welding is a complex craft that requires the utmost attention.
Investing in the right tools will make it easy and safe to get the job done. It is crucial for companies in the oil, gas, and mining industries to understand how to identify the most common welding defects, so they can act.