Weld Seam Defects: Classification and Remedies

Welding is one of the most important production processes. With its help, the connection of steel parts in a variety of designs. As in the case of other manufacturing processes, sometimes marriage occurs. It refers to defects in the welded joint, which can dramatically reduce the quality of the finished product, or even make its operation deadly.

Classification

By the way, how can they be divided? All defects in the weld seam are divided into three large groups:

• Outdoor.
• Internal.
• Through.

Outer defects in the weld seam are often the most numerous category. It includes: unnecessarily small dimensions, as well as shifting of the seam line, various inflows, "incisions", shrinkage shells and craters, porosity or cracks not welded during welding. The uneven width of the seam also applies to this variety. It is believed that external defects in welds are the least dangerous category.

Accordingly, the internal include: pores, numerous inclusions of slag, not completely cooked places, as well as cracks in the thickness of the welded metal. As for end-to-end defects, these are fistulas that pass through the entire thickness of the crack detail, as well as burns.

The main causes of welding defects

• Almost always they appear in the case when they try to use extremely cheap and low-grade materials.
• The same can be said for low-quality welding equipment. In addition, the frequency of defects is often increased after a poor repair of instruments used by specialists.
• Of course, this happens very often when there is a violation of the technology of work.
• Serious weld defects often occur in inexperienced professionals with low qualifications.

It is easy to understand that the best quality products are obtained in the case of fully automated equipment. Do not forget about the convenience of the workspace. Thus, a large scaly joint and breaches of its width are very often encountered when the welder (even experienced) works in an uncomfortable position.

Actually, it is no accident that there are points in the requirements for welding work that specifically stipulate the full equipment of the workplace, which provides for its high-quality ergonomics.

An important remark

Even novice welders are well aware that to ensure maximum strength, the seam should have a small reinforcement of a height of the order of 1-2 mm. At the same time, the same welders often make a gross mistake when they make a reinforcement with a height of 3-4 mm. In principle, in simple cases, there is nothing terrible about this, but not when it comes to products that are constantly in a state of dynamic loading. All this leads to stress concentration and a sharp increase in the probability of breakage.

Undercutting

As we have already said, defects in welds and joints are extremely dangerous. It is not difficult to imagine what will happen if they are present in a part intended for installation, for example, in the support structure of a railway bridge. Especially they are dangerous in the case of welding parts made of alloy steel, which will be used in conditions of constant temperature changes.

The most dangerous are undercuts, as they are a natural "accumulator" of stresses, which will concentrate in the weakest place of the seam. In addition, they significantly reduce its working cross-section, which also has a very negative effect on the strength of the entire compound.

As a rule, these external defects of welds in most cases are not corrected. This is due to the fact that metal (most often) will still have a low-grade marriage, which can lead to very significant consequences.

How are undercuts?

The main reason is to set too much current. In combination with a long arc, this factor gives almost a hundred percent probability of their appearance. In addition, in some cases, undercuts occur when the heating source is excessively rapidly moved above the surface of the metal.

If the design is at least as important, even the smallest defects of welded seams and connections of this type are completely unacceptable. Correct them with the help of a gentle welding of a thin seam. In the case of such an opportunity, the part is still better replaced completely (note that the last remark applies to all defects).

Unprocessed metal sites

If such a site is located directly in the thickness of the seam, this is extremely dangerous. First, it is possible to find such a defect only with the help of a flaw detector. Secondly, they again are accumulating places of natural stresses in the metal. In combination with the violation of the welded structure, all this leads to the risk of premature failure of the part. Especially often such internal defects of welds arise in the case of using alloy steel and poor welding equipment.

Porosity (regardless of its localization) sharply reduces the strength characteristics to unacceptable values, leads to a "stratification" of the metal, that is, to a violation of its natural structure. Details even with a slight porosity are several times more often destroyed under load even at the beginning of operation. Pores arise due to the fault of gases, which simply do not have time to leave the layer of molten metal.

Like all types of defects in welds, they are extremely common when using poor-quality raw electrodes. It often happens that the porosity arises because of some foreign impurities in protective gases. As in the past case, this type of defects can also be observed at an excessively high welding speed, when the integrity of the gas protective "bath" is corrupted.

Inclusion of slag

Inclusions of slag largely damage the uniformity of the metal structure. The classic reason for the formation is careless cleaning of the weld surface from rust and scale residues. The probability of their occurrence tends to zero under the condition of welding in the protective gas layer. Rare inclusions of a rounded form of danger do not represent, products with them can pass OTC.

Note that if a tungsten electrode was used in welding , then the particles of this metal can be found in details. The degree of their danger is the same as in the previous case (i.e., they are permissible defects of welded joints).

Cracks

There are transverse and longitudinal, going both along the seam and on the metal along or near it. They are extremely dangerous in that in some cases, reduce the mechanical and vibration strength of the product to almost zero. Depending on the properties of the material being welded, the crack can either retain its original localization or spread over the entire length of the workpiece in a very short time.

Not surprisingly, these are the most dangerous defects in welds. GOST in most cases requires the immediate rejection of such details, regardless of its purpose (with the exception of very small items).

Uneven seams

This is the name of the gross inconsistency of the geometric parameters of the joints with the characteristics required in the regulatory documents. Simply put, if welding goes "snake", obliquely, etc., it is just about a similar type of defects.

Most often, they appear when inexperienced welders work, as well as with significant voltage surges, poor-quality equipment and banal rush. This defect is dangerous because it is often combined with a nevado, which is much more dangerous. If the deviation from the center line of the connection is insignificant and does not cause a reduction in the strength of the product, the part can be approved for operation.

In this case one should always remember one simple thing: the smaller the angle of transition from the base metal to the fusion layer, the worse the mechanical strength of the welded product becomes. Of course, in the manufacture of some household structures (the frame of a greenhouse, for example) in conditions of insufficient stress, without uneven seams is simply unrealistic. However, in this case they do not pose a particular danger.

The basic ways of elimination, correction of defects

At once we will tell the following: in most cases ways of elimination of defects of welded seams to discuss does not make sense, as in more or less strict ОТК all products with any defects simply reject. But sometimes it does happen that the defect is not too serious, and therefore it can be eliminated. How to do it?

In the case of steel structures, the damaged surface is cut (plasma-arc welding), carefully clean the place of the failed connection, and then try again. If there are insignificant external defects of welded joints (uneven joints, shallow pockmarks), they can simply be ground. Of course, you should not get carried away and take off too much metal.

Important note

When it comes to products made of alloy steel, which must undergo mandatory heat treatment, correction of defects in welds must be carried out only (!) After tempering in the temperature range from 450 to 650 ° C.

Correction of other varieties

The easiest way to correct the influx and mechanical unevenness of the seam. In this case, the junction is simply cleaned (as we already mentioned). We already mentioned the corrections for the cuts, but once again we note that with such defects the part is more expedient to immediately reject, as its operation can be dangerous!

If there is a burn (which is not so common), then the elimination of defects in welded joints is simple enough: first, the surface should be cleaned properly and then re-welded. Approximately the same is done with craters.

Basic conditions of "cosmetic repair"

When eliminating defects, certain technological conditions must be observed. First, you need to follow a simple rule: the length of the defective area should match its width, plus 10-20 mm should be left "just in case".

Important! The width of the weld after its re-welding should not exceed two times its size before the start of work. Do not be lazy before fixing flaws to prepare the surface well. First, it will prevent the slag particles from getting into the metal. In addition, this simple measure will help to speed up the work and improve the quality of its results.

It is very important to prepare a sample for the newly embedded area. If you are using USM ("grinder"), then it is better to take a disc of the smallest diameter. The lateral faces of the sample should be made as level as possible, without burrs and other protruding parts, which in the process of welding can turn into the same slag.

If we are talking about the compounds of aluminum, titanium, as well as the alloys of these metals, then the matter should be approached even more responsibly. First, if defects are eliminated, only (!) Mechanical methods can be used in this case, while arc welding can not be used. It is preferable to cut down the damaged area, clean and re-weld the seam.

Note on corrected defects

Places with corrected - re-welded joints, must again undergo the procedure of OTC. If the defect is preserved to some extent, it can be tried again. Important! The number of corrections depends on the steel grade and the characteristics of the product itself, but under normal conditions the work can be changed no more than two or three times, as otherwise the strength of the part is sharply reduced.

So we discussed the main types of defects in welds.