Errors can always occur during welding. These can often be counteracted by simple means such as changing the welding parameters. So let's take a look at which errors occur most frequently and how they can be avoided.
Table of contents
How does insufficient penetration occur?
The defect of insufficient penetration occurs when the root of the weld seam does not reach to the mutual end of the components. This means that only part of the entire height of the edge is actually reached by the heat, liquefied and then joined.
This results in insufficient strength or durability of the entire depth of the weld seam and therefore the resulting joint. This can be prevented with one of three possible actions:
- The geometry of the connection can be changed. If, for example, the part of the "V" is cut out deeper when setting a Y seam, the edge is reached deeper by the heat. This allows the weld to reach the entire width of the edge, so that complete penetration is achieved.
- The welding speed can be reduced. This means that the energy introduced has more time to achieve the necessary heating at depth. As a result, the molten pool reaches more material so that the root reaches the other side of the edge.
- The current can be increased. More energy generates more heat, which leads to a deeper melt pool and thus to sufficient penetration of the root.
What does splash mean?
During welding, molten parts may be thrown away. This is due to the instability of the metal transfer. This can be countered by reducing the current.
This increases the penetration depth of the heat, but reduces the width of the penetration.
What happens if there is no connection?
A bonding defect describes the absence of a local connection between the workpieces. This can occur on the face of the deposited weld metal or on the seam flank. This means that the weld pool does not have sufficient time to enable a bond between the filler metal and the base material. This in turn can be counteracted in 4 ways.
- Reduce the welding speed. This gives the molten bath more time to mix and create the bond that then remains after solidification.
- Work with more power. More power means more heat, which means better liquefaction, which makes it easier to bond the substances so that there is no leakage.
- Change the geometry of the weld seam. This allows the heat to penetrate more easily and deeper. This increases the melting capacity and facilitates the mixing of the materials.
- Use special techniques. Depending on the material, they use different processes to prevent the formation of bubbles.
How does the containment of slag work?
If solid materials remain in the weld pool, regardless of whether they are metallic or not, they are trapped as slag. This is often due to the fact that the welding surface has not been sufficiently cleaned between several welding passes.
The inclusion of slag can also occur in a single-layer weld seam if it forms between the base and the root of the weld seam.
What is the back step?
With an undercut, a notch is formed on the side of the seam where it borders on the base material. This means that a trench is created on one or both sides of the weld seam. This can be counteracted in two ways.
The first step is to reduce the current. This makes the weld pool less deep, but wider, so that the weld seam is completely filled on both sides.
The second option is to reduce the welding speed. This allows for more thorough melting. This results in the joint being completely filled.
How do pores form?
Pores form when gases penetrate the molten pool and cause bubbles. If these remain in the melting zone, they become pores. This happens both on the surface of the molten pool and inside it.
Pores can be prevented by adjusting the flow rate of the shielding gas. You should also work with gases that have the necessary quality and therefore purity.
How do cracks occur?
During welding, cracks can form in the heat-affected zone or in the fusion zone. These can be caused by the contraction of the solidifying metal. Another cause is the growth of particles at the transition of the fusion zone. This is referred to as cold cracks, reheating cracks or solidification cracks. Here, reducing the welding speed can prevent the formation of cracks because it leads to better melting and slower solidification.
What is a warp?
Warping can easily occur in metal parts if they are heated incorrectly. This changes their shape or the position of certain parts in the workpiece.
Care must be taken to ensure that the temperature is generated at the right level in the right place to prevent warping of the parts involved.
How does the overlap occur?
An overlap occurs when the weld pool extends over the welding surface and thus exceeds the base of the weld seam. This means that the weld seam is wider than the joint. This is often because the electrode used is too large. It can also be due to poor welding technique.
What is burn-through?
A burn-through occurs when the molten pool penetrates the workpiece. This often happens when thin sheets are joined together. It also happens when too much tension is applied or the root opening is too large.
How are weld seams tested?
Weld seams are a permanent, stable connection between two or more workpieces. A complete whole is created from several parts. If you keep this in mind, you may quickly realize that it is both important and not easy to check these connections.
As the joints are permanent, you cannot simply open them up to look inside. Nor should you simply cut out a part of the new whole and look at the seam in cross-section.
It also makes little sense to subject the new connection to a load until it breaks. Although the quality can then be determined, the connection no longer exists after the test.
It is therefore important to use methods that can be used to check the weld seam without destroying it. There are at least 5 methods that can be used to do just that.
What is visual testing (VT)?
Visual testing is a process in which the weld seam is inspected optically. This means that the weld seam is examined with the naked eye or with optical aids such as mirrors and magnifying glasses.
In fact, many defects can be detected directly with a simple visual inspection. These include, for example, external cracks or pores on the surface. This makes the process useful and very easy to use.
How does magnetic particle testing (MT) work?
Magnetic particle testing or magnetic particle inspection involves testing magnetizable workpieces. The time required for this is minimal. Magnetic particles are used, which are applied directly to the component using a liquid or simply as a powder. If there are defects in the seam, the magnetic field changes and this is reflected in the alignment of the particles, which deviate from the rest of the good areas of the component.
Cracks or inclusions, even in non-magnetic materials, can be detected very quickly. Even small cracks with a width of only 0.001 mm or less and a depth of only 0.01 mm can be detected very easily. Incidentally, a human hair has a thickness that reaches or exceeds 0.04 mm for comparison.
What is penetrant testing (PT)?
Penetrant testing or penetration depth is a very flexible method. The capillary forces emanating from pores and cracks are used for this purpose. To apply the method, the component is cleaned. Then a penetrant with color or fluorescent is applied to it. This is done with a simple spray can, for example. A developer is then applied to the penetrant.
The penetrant is so fine that it creeps into even the smallest cracks, revealing them. When using this method, however, the environment must be taken into account. This includes the storage of the agents, their transportation and correct disposal.
Typically, the colors red and white are used. However, this method can only be used to a limited extent on rough or brittle surfaces. Here there is a risk of false indications or an indication intensity that leads to real cracks being overlooked.
How is ultrasonic testing (UT) carried out?
Ultrasonic testing uses ultrasound to take a direct look inside the component or weld seam. The ultrasound is applied to the material via a probe. The probe is moved over the surface of the workpiece. The ultrasonic waves penetrate deep into the material and their reflection can be tracked on a screen.
In the meantime, the process has evolved with computer technology into imaging ultrasound with a phased array. This creates a 3D image of the weld seam. In this way, the surface and the entire volume of the material can be checked.
How do X-ray and radiographic testing (RT/DR) work?
Radiographic testing and digital radioscopy make it possible to look inside the weld seam. The process generates an image that shows the quality of the joint.
For radiographic testing, an X-ray tube or other material is shone through the weld seam and the result is recorded on a film. Compared to ultrasonic testing, this has the advantage that it is easier to determine which defects are present. For example, it is easier to detect whether a pore or slag has been trapped in the weld seam.
Due to the use of radiation, comprehensive safety regulations must be observed during testing. This is why it is often carried out by specialized service providers.
Digital radioscopy works by means of an X-ray image intensifier or radioscopy system. This makes it possible to create the image digitally, store it and evaluate it immediately.
Who can carry out an audit?
There are special regulations for the inspectors who are allowed to carry out the corresponding inspection of weld seams. Certification takes place in three stages:
- Level 1: An examination procedure may be carried out and the results recorded.
- Level 2: A test procedure may be carried out and then assessed in accordance with the applicable standards and rules.
- Level 3: An examination procedure may be carried out and additional procedures may be selected. Procedure descriptions may be created for this purpose and the auditor assumes responsibility for setting up the examination.
Special demands are placed on the personnel who carry out the inspections. These include very good close vision and a good ability to distinguish colors. In addition, the inspector must act in accordance with ethical rules and must prevent damage to property.
Conclusion
A lot of defects can occur during welding, starting with insufficient penetration and even reaching inclusions of slag and the formation of pores. In order to inspect the welds without destroying them, there are various methods, including the use of ultrasound or X-ray technology. Inspectors must have very good eyesight and a high level of professional ethics.
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