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It is mainly assumed that the weld metal must be continuous. And all the formations that make the weld inhomogeneous are considered to be defects. There are the following types of weld defects: micro- and macrocracks (hot and cold), lack of penetration, pores, various inclusions.

Internal and external defects in welds

The most common method for classifying welding defects is by their location. According to this classification, internal and external weld defects are distinguished. The outer ones go to the surface of the seam and the near-weld zone, and the inner ones are located inside the joint without going to the surface. It follows from this that the same type of defects (for example, cracks or pores) can be both internal (if located inside) and external (if it comes to the surface).

External weld defects

The external defects of welded joints include the uneven shape of the weld due to its incorrect formation, undercutting of the weld, burns through the metal being welded, sagging, cracks, pores and other defects that are located on the surface of the metal. All of them are detected during external visual inspection of the welded joint. The text below lists and shows common types of external defects.

Internal weld defects

The internal defects of welded joints, according to GOST 23055, include non-metallic, slag and oxide inclusions, lack of penetration and non-melting of the metal, as well as pores and cracks that do not appear on the metal surface. In order to identify such defects, non-destructive welding testing methods are used in practice. The following text describes the most common types of internal defects.

Seam formation defects

Defects in the formation of welds are manifested in the unevenness of their shape (see figure on the right). They are formed due to non-constant welding modes, non-constant gap between the edges to be welded and an uneven bevel angle of the edges. The discrepancy between the actual shape of the weld and the required one may manifest itself due to incorrect, due to the incorrect location of the electrode relative to the weld edges.

A similar defect may occur with others. For example, in automatic welding, the cause of such a defect can be the slip of the welding wire in the feeder, the voltage drop in the network, the ingress of molten metal into the gaps, etc.

Weld gap

Most often, lack of fusion in welds occurs in cases where there are small gaps between the welded edges, with a large blunting of the edges, and also if there are impurities on them, with the electrode or welding wire in the wrong position relative to the edges to be welded, with insufficient welding current and with high welding speed.

Very often, lack of penetration is formed at the root of the seam (scheme a) and b) neither in the figure on the left and schemes c) and d) in the figure). In automatic submerged arc welding, lack of fusion, in most cases, is formed at the beginning of the weld. To prevent their occurrence, it is recommended to weld on special linings. Lack of penetration is one of the most dangerous defects for a welded joint.

Weld undercuts

Weld undercuts are formed on the joint surface. Undercuts are recesses in the base metal located along the edges of the weld. They appear due to the excessively high strength of the welding current and due to the large length of the electric arc, because. in this case, the width of the weld increases and the edges of the weld edges melt more strongly.

There are several types of weld cracks:

Type of weld defect. As well as its size and place of its occurrence.

Mechanical properties of the welded joint. These are tensile strength, fluidity, impact strength, ductility, corrosion resistance, fatigue fracture resistance, etc.

The conditions under which the product is used. Basically, it is the nature of the environment.

Functions to be performed by the product. There is even such a term: "suitability for a given purpose." Those. the same defect in a weld may be acceptable for one task, and unacceptable for another.

In order to make a decision about the acceptability of defects of one type or another and size, it is necessary that the measuring ability of the device for monitoring defects be higher than the allowable size of the defect. That is, if defects are allowed in the weld, no more than 2 mm in size, then a device with a measuring capacity of 5 mm cannot be used to control this seam.

In order to determine the maximum value of a permissible defect, it must be borne in mind that defects in welds increase mainly the ability of steel to fatigue and brittle fracture.

For destruction of this type, planar defects (microcracks, macrocracks, lack of penetration) pose the greatest danger. If they are detected, it is necessary to pay attention not only to the maximum dimensions of individual defects, but also to their relative position and their number.

The danger of planar defects lies in the fact that they are high stress concentrators due to the absence of a rounding radius near cracks. Spatial defects, such as pores, gas bubbles or any inclusions have some kind of radius of curvature, therefore, are less of a hazard, even with a larger number.

With a small rounding at the base of the crack, in order to evaluate the stresses acting in it, the stress intensity factor K1 is used, which makes it possible to evaluate the fracture mechanics. The stress intensity factor can be determined if the stress required for fracture is less than the yield strength of the material. It is determined by the formula:

where a is the size (height) of the external defect, or half the size of the internal defect;
bm - tensile stress;
bv - bending stress;
Мm and Мв - coefficients, the value of which is determined by the ratio of the size of the defect to the thickness of the part and the location of the defect;
Q is a coefficient depending on the shape of the defect.

For welded joints that are not annealed after welding, in order to reduce internal stresses, it is necessary to use the calculation of the critical crack opening (COD) to assess the acceptability of weld defects. The calculation of the coefficient K1, or finding the value of the critical opening, makes it possible to determine with high accuracy the value of a possible allowable defect in the weld.

In the course of welding, as in any other methods of metal processing, defects in welding seams, which are formed for a number of reasons, cannot be ruled out.

The list of factors affecting the quality of a welded joint is very extensive, but the main cause of defects is uncontrolled chemical processes occurring in the boundary regions of the welding zone.

The cause of defects can be the crystallization of the metal, its chemical heterogeneity, as well as the interaction of the molten mass with the solid material of the workpieces or with the surrounding gases and slags. Another reason for the appearance of defects (cracks, in particular) that needs to be taken into account is undesirable stresses in the welding zone.

The nature of deviations of welded joints from the norm (defects) depends on . This is due to the technological features of a particular process.

The difference is quite clearly manifested in all its main types, namely, in electric arc processing of metals, contact welding of sheet blanks, and, finally, in gas welding.

Arc method

Two main factors can be attributed to the main reasons for the formation of defects at . These are chemical reactions that lead to a violation of the structure of the seams, as well as serious deviations from existing technologies.

Welding defects that occur in the second case most often manifest themselves in the form of burns, lack of fusion and violations of the geometric dimensions of the seam or cracks that occur after the material has cooled.

The process of formation of cold cracks during welding is explained by unacceptable mechanical loads on the seam joint. Such deviations from the normal structure of the seam are most often observed when welding carbon (alloy) steels, as well as most cast iron products.

In general, in the theory of electric arc welding, a variety of violations of the structure of the welded joint are considered. In addition to the so-called "cold" cracking, such defects include "hot", macroscopic and microcracks.

All of the listed deviations from the norm over time lead to the expansion of the defect coverage area and emergency destruction of a poorly welded structure. For this reason, increased attention is paid to the study of the quality of welds formed during arc welding.

gas welding

The main causes of defects that appear during gas welding are most often the same as in the cases listed earlier regarding other categories of welding work.

These are the same violations in the technology of preparation of blanks before fusion and errors made during the formation of the seam (due to the use of non-standard consumables, for example).

That is why, in order to prevent gas welding defects, special attention is paid to the competent choice of the correct welding mode, as well as the skill level of the work contractor himself.

According to the availability of detection of violations during gas welding, all known defects are divided into surface and hidden. The first category includes typical lack of penetration, significant influxes, as well as concavities, cuts, craters formed on the base (at the root of the seam).

This should also include an unacceptable displacement of the joint line (their incorrect cutting), sharp differences in thickness and surface cracks.

Hidden and, as a rule, difficult to detect defects in gas welding include internal porous formations, microscopic gas channels, as well as slag and oxide inclusions.

This list can be continued by such frequently occurring violations of the structure of welded workpieces, such as inconspicuous lack of penetration between layers and internal microcracks.

Point contact method

The following visually distinguishable (external) violations in the structure of joints are commonly referred to as resistance welding defects:

• cracks visible to the naked eye;
• spot burns;
• outdoor splashes;
• metal ruptures with a surface manifestation of the structure;
• violations of the contact form and many others.

The main reasons for the appearance of such deviations in the structure of the contact are incorrect setting of the parameters (amplitude or duration) of the pulsed current, insufficient force when compressing the electrodes.

Defects are caused by poor-quality preparation of the treated surfaces before welding, the proximity of the contact point to the edge of the spot connection.

Other reasons include insufficient workpiece overlap, unacceptable misalignment of the jointed parts, wear of the electrodes, and much more.

The main hidden defect in welding by contact methods is the "sticking" of sheet blanks, in which only an apparent, purely external contact is formed between them. This defect can manifest itself not only in pressure welding, but also in other known types of spot welding.

It is practically impossible to visually detect this type of defect formation by conventional methods of physical control. It can be prevented only by strict adherence to the technology and maintaining the main parameters of the welding process (amplitude and duration of the pulsed current, as well as the necessary compression force) in normal conditions.

Correction and prevention

The presence of defects in any type of welding does not always lead to an irreparable result and rejection of the workpiece. There is a certain set of process violations or deviations from the norm, which can be corrected immediately after the completion of the process.

The simplest and cardinal way to correct any flaw during welding is to cut out the rejected area and re-weld it (taking into account the detected malfunction, of course). To eliminate or correct a number of defects, it is quite enough to correct the position of the working tool with the electrode.

When using this technique, it should be remembered that welding by the “uphill” method contributes to the redistribution of molten metal in the pool area, and work by the “forward angle” method allows to reduce the penetration depth.

Since additional costs will be required to correct the marriage, it is advisable to organize the welding process in such a way as to eliminate the need for repeated work.

One of the most effective ways to prevent defects is to add one of the components when welding in a protective environment, which allows you to increase the fill factor of the seam and prevent possible undercuts.

To increase the fluidity of the liquid metal, which ensures the filling of the root part of the weld, it is enough to preheat the welding site to a certain temperature using special additives (fluxes).

It is often possible to achieve the desired effect by increasing the current strength. At the same time, thorough cleaning of the welded edges and removal of oxide films from their surface also reduce the likelihood of violations of the welding mode.

Cutting cracks

To eliminate cold cracks, the method of their re-welding is used with limitation of the expansion of the defect area on both sides (preparation of special "catchers").

Such traps are made in the form of small holes drilled at a distance of about 1.5 cm from the edges of the formation, capable of slowing down or completely stopping its growth.

Repair of cracks involves a certain order of operations, taking into account the need for careful preparation for re-welding. At this stage, the edges prepared for restoration are first cut at an angle of 60 °.

To carry out this operation, either a conventional chisel or a special cutting electrode is used, by means of which the cut edges are completely cleaned of all formations and irregularities that interfere with fusion.

It is not necessary to remove the previously drilled limiting holes-traps.

The presence of welding defects, as a rule, leads to a decrease in the strength characteristics of the joint being prepared, and, as a result, to a violation of the structure's operability (its increased accident rate). That is why the issue of detecting and correcting defects is always given special attention.

They negatively affect the quality and durability of the manufactured metal structure, provoking its deformation and destruction over time.

Therefore, welding must be performed in such a way that the created joints are of the highest quality and accurate, without flaws.

If it didn’t work out skillfully, it’s worth asking if there are reliable ways to eliminate welding defects and study them.

Weld defects are flaws on the surface or inside the seam created by the use of welding equipment.

They can have a different degree of severity, shape, size and lead to a decrease in useful life, can affect its operational parameters, and therefore are highly undesirable in operation.

External defects in welds.

The appearance of welding flaws can be explained by various reasons:

1. The created joints may be of low quality if the master does not have extensive experience in welding operations: violates the technology of electric arc, argon, beam welding, neglects the preparatory process, heat treatment of components, confuses the assembly scheme of parts, selects the wrong mode of operation of the welding machine during laser welding, etc. P.
2. Also, poor weld performance may be the result of the use of handicraft or faulty equipment for manual arc welding, low-quality metal, and cheap consumables.

All seam defects are called differently and are conditionally divided into several groups, each of which has a certain type and features:

• outdoor;
• internal;
• through.

The features of the deficiency will determine the most appropriate way to correct it. To prevent such problems in the future, it is important for the welder to work on the mistakes and understand what led to such sad results in his work.

Important! Not every problematic section of a seam is considered an unacceptable flaw. Based on the list of requirements for welded joints and metal structures in general, there are permissible defects.

These are flaws that are not able to affect the quality of the welding joint. But their number in any case should be minimal in order to maximize the service life of the product.

Species diversity of defects

An inexperienced welder in the process of creating semi-automatic welded joints may encounter various types of welding defects. They differ in external characteristics and appear due to a violation of the welding technology: manual arc welding, automatic, etc.

Causes of defects in welds.

It is important to carefully study such problems, which will prevent damage to the parts to be welded during manual arc welding and the implementation of other technologies for creating joints in metal structures in the future.

• external: cracks, undercuts, sagging, craters, scale, welded shells;
• internal: porous structure, insufficient penetration, foreign inclusions;
• through: cracks, burns.

External flaws have this name, as they are on the front side of the connection and are visible to the eye. To detect them, it is enough to conduct a visual inspection of the part. Internal defects are located inside the welding joint, so they are not immediately noticeable.

The presence of this problem can be determined using flaw detection of welds, including ultrasonic, mechanical and X-ray processing. Cross-cutting flaws are the most catastrophic, since their elimination is not always carried out 100%.

External defects

If the welding technology is violated and consumables of poor quality are used, the following welding defects can be obtained: sagging, undercuts, unwelded craters, surface pores, burns, cracks, etc.

The sags are the result of the flowing of the molten metal of the weld wire onto the unmelted base metal of the structure or a pre-made bead.

Such shortcomings can be local in nature and manifest themselves in separate zones, or they can acquire an elongated shape and occupy a decent area on the metal product.

The main reasons for the appearance of influxes are as follows:

• the welder incorrectly set the current strength with a long arc and made a mistake with the selection of the speed of the equipment;
• an excessively large slope of the plane on which the weld was applied was chosen;
• the electrode was incorrectly led, or it changed its original position when making circumferential welds under the flux;
• the welder had insufficient experience or worked in an uncomfortable spatial position: vertical or horizontal.

Undercuts are depressions on the surface of the main, running along the edges of the weld. The depth of the cut can vary between 0.1-1 mm.

The reasons for the formation of such defects in welded joints are:

• excessively high current;
• arc voltage above the norm;
• uncomfortable posture of the welder in spatial terms;
• carelessly welded.

The presence of such errors is dangerous, since undercuts can reduce the working thickness of the metal at the junctions of metal parts, provoke the appearance of local stress concentration from work loads and cause deformation of welds over time.

Names of weld defects.

We also note that undercuts of butt and fillet welds located across the forces acting on them can cause a sharp decrease in the vibration strength of the joints.

Crater - a dent that appears in the event of a sharp break in the arc at the end of welding. Very often this problem occurs when creating short seams.

The size of the crater is determined by the value of the welding current:

• with a manual welding method, its diameter is 3-20 mm;
• during automatic welding, the crater takes the form of an elongated groove.

Important! If such a defect is not welded, the strength of the welded joint and the cross section of the seam will decrease, and this will entail the appearance of foci of cracking.

Burn-throughs are the penetration of the base or deposited metal, on which through holes are sometimes formed.

The causes of these defects are:

• insufficient blunting of the edges, a large gap between them;
• overestimated welding current or burner power against the background of low welding speeds;
• insufficient compression of the flux pad, copper lining during automatic welding;
• during excessively long welding, insufficient compressive force, in the presence of contamination on the surfaces of welded parts, wire during spot and seam resistance welding.

Especially often, burns can be observed when welding thin metal, when organizing the first pass of a multilayer weld. Such defects can be eliminated, but even after that, the connection does not acquire satisfactory characteristics and aesthetic appearance.

Therefore, it is worth initially making every effort to prevent the appearance of such defects on the surface of the weld.

On a note! Separately, it is worth noting such a defect as a crack in the welded joint. We will answer what is called a crack: a violation of the plane of the metal, provoked by cooling, by the action of loads. It can apply to both external and internal welding defects.

It is possible to detect external defects on welds using visual-measuring control, capillary flaw detection, as well as other non-destructive testing methods: X-ray, ultrasound.

Internal defects

Varieties of welded joints.

Internal welding defects include:

1. Cold cracks.
   They appear only after cooling and solidification of the welded joint due to its inconsistency with the acting loads.
2. Hot cracks.
   They appear at the moment when the metal of the welded joint is in a state between the melting and solidification temperatures due to the use of a low-quality additive, incorrect crater welding technology, due to an abrupt stop of the welding process, due to burns during welding. Such defects can have several types of location: along and across the connection of metal parts.
3. Pores.
   They can occur with any welding technology due to the presence of contamination on the surface of the parts to be joined, poor protection of the weld pool with gas flow, oil, paint, welding of incompatible alloys, rust and metal oxidation. The pores vary in size and often have a chaotic distribution over the weld: they are located both inside the joint and on its surface.

The elimination of identified defects in welding seams that are invisible to the eye must be carried out after determining the main causes that provoked the appearance of the defect, regardless of the fact whether the technology was carried out or another type of welding operations was used.

This will allow you to choose the most effective method of dealing with the problem and prevent such errors in the future.

through

Through defects are holes in a metal part, which are formed due to improper welding. The master selects the wrong mode of operation of the welding machine and burns the metal through.

Also, such problems arise when welding stops suddenly, when operations are carried out in drafts, and when working with thin metal.

Through resistance welding defects are:

• undercut when welding;
• crack;
• burn through .

How to detect weld defects?

You can detect a defect in a welded joint in the following ways:

• visual inspection is carried out using a magnifying device and allows you to detect even tiny defects in spot welding;
• flaw detection of welds - a method for diagnosing the quality of a weld, based on the tendency of a special material to change its color at the moment when it comes into contact with a fluid material, for example, kerosene;
• method - performing measurements of the distortion of magnetic waves;
• Ultrasound - ultrasonic testing involves the use of special ultrasonic flaw detectors that can measure the degree of reflection of sound waves;
• The radiation method is carried out by X-raying the weld seam, obtaining a picture that describes all the details of the problem area.

Beads on the inside and outside of the weld.

Color flaw detection and ultrasonic testing of welded joints are considered the most effective methods for detecting defective welded joints, but it is almost impossible to implement them in domestic conditions.

Elimination of defects in welds

Almost all defects in welded joints, with the exception of the most insignificant in size, require elimination.

If this is not done, the operational parameters of the seams and the metal structure itself will deteriorate significantly: the presence of welding defects can lead to deformation of the metal, its rapid destruction under mechanical pressure.

Varieties of shortcomings will determine the methods of dealing with them.

Types of defects in welded joints.

Therefore, we characterize the most common welding defects and how to eliminate them:

1. Deviations of the parameters of the seams from the norms in width, height, leg, constriction of joints.
   They are identified by carrying out an external examination of the seams, analyzing their sizes using templates. You can eliminate the defect by cutting off excess metal, cleaning the seams, and welding the bottlenecks of the joint.
2. Undercuts are a recess along the line of fusion of the working and base metal.
   An external examination of the seams will help to find the problem, and it will be possible to eliminate it if you perform a high-quality cleaning of the undercut and welding the seam itself.
3. The time of the weld is a round-shaped cavity with gas.
   Sometimes several pores are connected in a chain. The method of detection and methods for eliminating defects of this kind: visual inspection, inspection of a fracture in the seam.
4. Fistulas in the form of a funnel-shaped depression are detected during external examination, removed by cutting, gouging with further cleaning and welding.
5. Lack of penetration appears due to insufficient melting of the edges of the welded joint.
   It is possible to eliminate the defect after visual detection, finding out the cause of the formation of lack of penetration. The method of control during laser welding will prevent the use of a defective part, and lack of penetration is eliminated by cutting and pulling out, cleaning and welding.
6. The sags on the welds have the form of leakage of the weld metal on the surface of the working metal.
   They are effectively identified and eliminated by conducting an external examination, hemming and removing the influx, and unfinished areas will need to be welded.
7. Slag inclusions are defects in the form of slag inclusions.
   Such a problem can be identified and eliminated by visual analysis of the part, X-ray and gamma control, control by an ultrasonic unit, and magnetographic equipment. Slag from the defective area will need to be removed, cleaned, welded.

Summing up

Weld defects occur when the welding technology is violated and endanger the stability of the weld and the functionality of the entire metal structure.

For this reason, it is important for a self-respecting craftsman to learn the main defects of the seams - the appearance of pores, sagging, burnouts, etc. - and the reasons for their formation during the welding process.

This will allow you to choose the most effective solution to eliminate the shortcomings of joints in spot welding, the use of a laser, an electric arc, argon, etc.

When welding various metal structures, the quality of the welded joints made on them is of particular importance.

Along with the mechanical properties and corrosion resistance of welded joints, the absence of defects in the weld, fusion zone, and heat-affected zone is one of the most important factors determining the performance of welded structures.

Weld defects in fusion welding are divided into:

Defects in preparation and assembly;

Seam shape defects;

Defects in the structure of the metal of welded joints (external and internal).

Defects in preparation and assembly are most often caused by:

Violations of the geometry of the bevel edges of the seam;

The inconsistency of the gap between the edges along the length of the joined elements;

The mismatch of the planes of the joined parts.

Defects in the shape of the seam (undercuts, sagging, burns, shrinkage grooves, etc.) are primarily due to:

Uneven width of the seams formed in violation of the technique of movement of the electrode;

The uneven gap of the edges during assembly, the unevenness of the bulges along the length of the seam, local thickenings and depressions (first of all, they depend on the unsatisfactory quality of the electrodes in manual welding and the instability of the machine mechanism in automatic welding).

For students of welding specialties, it is necessary to clearly know the characteristic types of defects (external and internal), the reasons for their formation and ways to prevent and eliminate them; the influence of various defects on the properties of the welded joint.

The given illustrations (diagrams and photographs) of defects allow you to quickly and reliably visually identify the type of defect, establish the causes of occurrence and promptly take measures to eliminate it.

Fusion welding defects are classified according to their location into surface, internal and through.

Surface defects include:

- lack of penetration at the root of the seam;

undercuts; influxes;

Craters; underestimation (weakening) of the front surface of the seam;

Concavity of the root of the seam;

Offset of welded edges;

A sharp transition from the seam to the base metal (wrong pairing of the weld);

splashes of metal; surface oxidation; surface cracks.

Internal defects include:

Pores; inclusions;

oxide films;

Internal cracks;

Lack of penetration along the edge with the base metal and between individual layers;

Through defects include cracks and burns.

In addition to defects - discontinuities, defects in fusion welding include: distortion of the shape of the joint associated with deformation, and discrepancy between the geometric dimensions of the weld or points, the regulated values ​​established by the NTD (normative and technical documentation).

GOST 30242-97 provides a classification, designation and a brief description of defects in welded joints, a three-digit numerical designation of defects and a four-digit designation of their varieties, a letter designation of defects, the name of defects in Russian, English and French, an explanatory text, drawings that supplement the definitions.

When choosing methods and means of controlling joints made by welding, it is necessary to have a clear idea of ​​the nature of defects and the reasons for their occurrence. The most characteristic defects that occur during fusion welding are listed in Table. 21.1.

Table 21.1. Fusion Welding Defects

Continuation of table 21.1.

Continuation of table 21.1.

Continuation of table 21.1.

End of table 21.1.

In accordance with the specified standard, defects are divided into six groups, mainly according to their shape and location in the welded joint (Table 21.2):

1. cracks;

3. solid inclusions;

4. non-fusion and lack of penetration;

5. violation of the shape of the seam;

6. other defects.

Table 21.2. Types of defects (in accordance with GOST 30242-97)

Continuation of table 21.2.

Continuation of table 21.2.

End of table 21.2.

Cracks. Types of cracks

Cracks are among the most dangerous defects and, according to all normative and technical documents in welded joints, they are considered an unacceptable defect.

A crack is a discontinuity in a welded joint in the form of a gap in the weld or adjacent zones.

Cracks in accordance with GOST 30242-97 are divided according to orientation to the seam into:

Longitudinal, oriented parallel to the axis of the weld and located in the weld metal, at the fusion boundary, in the heat-affected zone and in the base metal (Fig. 21.1 and 21.2);

Transverse, oriented across the axis of the weld and located in the weld metal, in the heat-affected zone, in the base metal;

Radial - radially diverging from one point and located in the weld metal, in the heat affected zone, in the base metal.

According to the temperature of crack formation, there are the following types:

Hot, arising in the temperature range of liquid metal crystallization;

Cold, arising at temperatures below the metal crystallization range;

Reheat cracks.

Rice. 21.1. Longitudinal and transverse cracks in the weld metal

Rice. 21.2. Location of cracks along the weld cross section in electroslag welding:

a- along the axis of the seam; b– between branches of columnar crystals

Rice. 21.3. Cracks in the fracture of the seam: a- coming to the surface of the seam; b- not exposed to the surface of the seam

Rice. 21.4. Location of cracks along the weld cross section (arc welding): a- cracks that do not go to the surface of the seam; b- cracks that go to the surface of the seam

The further operation of the structure depends on the quality of welding, therefore defects in welded joints are not allowed. Many factors contribute to the occurrence of defects, for example:

• violation of work technology;
• negligence;
• low qualification of the welder;
• use of faulty equipment;
• performance of work without proper preparation, in adverse weather conditions.

Permissible and non-permissible values ​​of defects in welds are distinguished from the degree of reduction in the technical parameters of the product in terms of strength. In case of permissible violations, welding defects are not corrected; in the second case, their elimination is necessary. The suitability of the product for operation, the determination of the compliance of the seam with the standards is carried out in accordance with GOST 30242-97.

Types of welding defects

The correct welding seam implies the uniformity of the composition of the base and filler material, the formation of its desired shape, the absence of cracks, lack of fusion, influx, the presence of foreign substances. There are the following types of defects in welded joints:

• outdoor;
• internal;
• through.

What are external defects?

External defects in welds and joints are detected visually. Violations of the welding mode, non-observance of the accuracy of the direction and movement of the electrode due to the haste or irresponsibility of the welder, fluctuations in the voltage of electricity during welding lead to the formation of a seam of the wrong size and shape.

The characteristic features of the external appearance of the marriage are: the difference in the width of the longitudinal seams and fillet legs, the sharpness of the transition from the base steel to the deposited.

With the manual method of welding, violations occur due to errors in the preparation of edges, neglect of the welding mode and speed, and the lack of timely control measurement. Defects in welds and the reasons for their formation during the automatic or semi-automatic welding method lie in excessive power surges, errors in the mode. There are the following external types of defects in welds:

cracks seams are hot and cold, longitudinal, transverse, radial. The first of them take place when applying high temperatures from 1100 to 1300°C, affecting the properties of the metal in terms of reducing plasticity, the appearance of tensile strains. This type of weld defects is accompanied by an increase in the composition of undesirable chemical elements in the steel. Cold cracks can appear at temperatures up to 120°C during cooling, later - under the influence of loads during operation. The reason for this type of marriage may be a decrease in the strength of the steel due to welding stresses or the presence of dissolved hydrogen atoms.

Crack in the weld

undercut characterized by the presence of a recess between the alloyed and base steel. This type of weld defect is more common than others. An increase in arc voltage during fast welding leads to a thinning of the steel thickness, a decrease in strength. A deeper penetration of one of the edges causes the liquid steel to run off to the other surface, due to which the welding groove does not have time to fill. In this case, welding defects and ways to eliminate them are determined visually. Deficiencies in the work are eliminated by stripping, followed by overcooking.

Undercut welding seam

influx occurs when the fused metal flows onto the surface of the base steel without forming a homogeneous mass with it. This type of marriage is characterized by the formation of a seam outline without gaining sufficient strength, which affects the overall endurance of the metal. The reason for the marriage is the use of low arc voltage, the presence of scale on the edges of parts, the leakage of melted steel when welding horizontal seams, when the surface of the welded structures is vertical. Excessively slow welding also leads to the formation of sagging, due to the appearance of excess molten metal.

craters appear due to a sharp separation of the arc. They have the form of depressions, where lack of penetration, friability of the material with a shrinkage property, leading to the appearance of cracks, can form. Craters occur due to welder errors. Since the crater is usually the cause of cracking, which is why it is not allowed, if it is found, it should be cleaned, then re-welded.

The resulting crater in the weld

Fistulas have the form of funnels with a recess on the body of the seam. They are formed from shells or pores of sufficiently large sizes, with insufficient preparation of the surface of the welding elements and filler wire. This type of defect can also be seen during visual inspection and must be immediately eliminated.

Typical funnel fistula

Internal defects in welds

Internal flaws in welding cannot be visually detected. They usually appear due to a violation of the welding process and inadequate quality of the material. With internal defects, cracks may also appear, but they are not visible or small, but may open up over time. Hidden cracks are dangerous because they are difficult to detect, and the stress can increase gradually, and can lead to transient destruction of the structure, therefore they are extremely dangerous. The cause of marriage can be huge stresses, rapid cooling when using carbon and alloy steels. The most common types of this kind of defects are as follows:

Lack of fusion occurs when there is insufficient fusion of the welded parts of the seam in places. The reason lies in the improper preparation of the edges associated with the presence of rust, scale, lack of clearance and dull edges. In addition, haste and fast welding speed, low current or displacement of the electrode from the axis of the seam can also lead to lack of penetration of the seam. Due to a decrease in the cross section of the weld, a stress concentration appears, which is reflected in a decrease in the strength of the joints, which is up to 40% under vibration loads, and large areas of lack of penetration - up to 70%. If the permissible values ​​\u200b\u200bare exceeded, cleaning of the seam and its overcooking is required.

Lack of penetration and non-filling

pores are the free spaces of the weld, filled with gas, mainly hydrogen. The reason for this type of marriage is the presence of foreign impurities in the materials being welded, dampness, insufficient protection of the weld pool. If the allowable pore concentrations are exceeded, the weld seam must be overcooked.

Pores in the weld

In addition, slag, tungsten, oxide inclusions can also be noted, which also occur when the welding process technology is violated.

Through defects

This type of marriage implies the presence of pores passing through the entire thickness of the weld, which are also detected visually. Predominantly occur during the conduct of through welding. With this type of defect, burns and cracks may appear.

Burn-through occurs from the use of high current and slow welding. The reason is the excessive openness of the gap at the edges, the loose fit of the linings, as a result of which the weld pool leaks. Checking the seam for the presence of marriage is carried out visually, if it exceeds the permissible norm, cleaning and overcooking of welding is required.

Methods for detecting, controlling and eliminating defects

To detect weld defects, the following methods are used:

1. visual inspection - carried out using magnifying instruments;
2. color flaw detection - based on a change in the color of a special material in contact with a fluid material, for example, kerosene;
3. magnetic method - measurement of the distortion of magnetic waves;
4. ultrasonic method - the use of ultrasonic flaw detectors that measure the reflection of sound waves;
5. radiation method - X-ray transmission of welds and obtaining a picture with all the details of the defect.

To ensure the quality of the weld, marking and branding are carried out. Each welder puts his stamp on his welding area.

If a marriage is found, it is necessary to eliminate welding defects. For this, the following types of work are used:

• welding - used to eliminate large cracks, having previously prepared the crack by drilling and cleaning with a chisel or abrasive tool;
• internal small cracks, lack of penetration and inclusions are subject to complete cleaning or cutting with re-welding;
• incomplete seams and undercuts of the weld are eliminated by surfacing or welding in thin layers;
• removal of sagging is carried out mechanically using an abrasive tool;
• overheating of the metal is eliminated by heat treatment.