What are Weld Undercuts?

GOST R ISO 6520-1-2012 welding and related processes. classification of geometry and continuity defects in metallic materials. Part 1. Fusion welding, GOST R dated November 22, 2012 No. ISO 6520-1-2012

GOST R ISO 6520-1-2012

OKS 25.160.40

Date of introduction 2014-01-01

1 PREPARED BY the Federal State Institution “Scientific and Educational Center “Welding and Control” at the N.E. Bauman MSTU (FGU “NUTSSK” at the N.E. Bauman MSTU), the National Agency for Welding Control (NAKS), Autonomous Non-Profit organization “The Main Certification Center for Welders and Welding Production Specialists” on the basis of its own authentic translation into Russian of the international standard specified in paragraph 4

2 INTRODUCED by the Technical Committee for Standardization TC 364 “Welding and related processes”

3 APPROVED AND ENTERED INTO EFFECT by Order of the Federal Agency for Technical Regulation and Metrology dated November 22, 2012 N 1012-st

4 This standard is identical to the international standard ISO 6520-1:2007* “Welding and related processes. Classification of geometry defects in metallic materials. Part 1.

Fusion welding" (ISO 6520-1:2007(E/F) "Welding and allied process - Classification of geometric imperfections in metallic materials - Part 1: Fusion welding)________________

* Access to international and foreign documents mentioned in the text can be obtained by contacting the User Support Service. — Note from the database manufacturer.

5 INTRODUCED FOR THE FIRST TIME

The rules for applying this standard are established in GOST R 1.0-2012 (section 8). Information about changes to this standard is published in the annual (as of January 1 of the current year) information index “National Standards”, and the official text of changes and amendments is published in the monthly information index “National Standards”.

In case of revision (replacement) or cancellation of this standard, the corresponding notice will be published in the next issue of the monthly information index “National Standards”.

Relevant information, notices and texts are also posted in the public information system - on the official website of the Federal Agency for Technical Regulation and Metrology on the Internet (gost.ru)

Introduction

The international standard ISO 6520-1 was developed by technical committee ISO/TK44 “Welding and related processes”, subcommittee SC7 “Terms and definitions”.

This second edition of the standard replaces the first edition (ISO 6520-1:1998), which has been revised.

The ISO 6520 series of standards includes the following parts, grouped under the general title “Welding and related processes. Classification of geometry defects in metallic materials":

— Part 1 Fusion welding;

— Part 2 Pressure welding.

1 area of ​​use

This part of ISO 6520 is the basis for the classification and description of welding defects.

For a more accurate classification of defects, explanations and, if necessary, sketches are provided.

Metallurgical defects are not considered.

Another defect designation system is possible according to the ISO/TS 17845 standard.

Annex B contains the relationship between the classification of defects in this standard and the notation system according to ISO/TS 17845.

NOTE In addition to the names in two of the three official ISO languages ​​(English and French), this part of ISO 6520 also contains a corresponding name in German.

2 Terms and definitions

The following terms with corresponding definitions are used in this standard:

2.1 defect (imperfect ion): Discontinuity in a welded joint or deviation from the required geometry.

2.2 unacceptable defect : A defect that exceeds the norm.

3 Classification of defects and explanations

The basis of the system for designating defects, given in Table 1, is their classification into 6 main groups:

— 1: cracks;

— 2: cavities;

— 3: solid inclusions;

— 4: lack of fusion and lack of penetration;

— 5: deviation of shape and size;

— 6: other defects.

Table 1 shows:

- in column 1 - a three-digit serial number for the main group of defects and a four-digit serial number for subgroups;

- in column 2 - the name of the defect in Russian, English, French and German;

— in column 3 — definition and/or explanatory text;

- in column 4 - drawings supplementing the definition, if necessary.

4 Types of cracks

Types of cracks depending on the reasons for their formation both during and after welding are presented in Appendix A. Letter designation.

If a complete description of cracks is required, then a combination of the numerical designation from Table 1 with the letter designation of Appendix A should be used.

5 Designations

The following form is used to indicate defects: Crack (100) is indicated as follows: defect ISO 6520-1-100 .

Table 1 - Classification of defects

Defect designation	Name of defect	Definition and/or explanation of the defect	Drawings of welds and joints with defects
Group N 1 - Cracks
100	Crack	Discontinuity caused by local rupture due to cooling or stress
Crack
Fissure
Riss
1001	Microcrack	A crack visible only under a microscope
Microcrack
Microfissure
Mikroriss
101	Longitudinal crack	Crack oriented parallel to the weld axis
Longitudinal crack
Fissure longitudinale
	A longitudinal crack can be located:
1011	in the weld metal
1012	at the fusion boundary
1013	in the heat affected zone (HAZ)
1014	in base metal
102	Transverse crack	Crack oriented perpendicular to the axis of the weld
Transverse crack
Fissure transversal
Querriss	A transverse crack can be located:
1021	in the weld metal
1023	in the HAZ
1024	in base metal
103	Radial cracks	Cracks radiating from one point
Radiating cracks
Fissures rayonnates
Risse	Radial cracks can be located:
1031	in the weld metal
1033	in the HAZ
1034	in the base metal.
NOTE: Small radial cracks are also called “star” cracks.
104	Crater crack	Crack in the crater at the end of the weld
Crater crack
Fissure de
Endkraterriss	A crater crack can be:
1045	longitudinal
1046	transverse
1047	radial (star-shaped)
105	Scattered cracks	A group of unconnected cracks oriented in different directions
Group of disconnected cracks
de fissures
Unconnected cracks can be located:
1051	in the weld metal
1053	in the HAZ
1054	in the main material
106	Branched crack	A group of connected cracks radiating from one common crack, different from a group of unconnected cracks (105) and from branched cracks (103).
Branching crack
Fissure
Riss	A branched crack can be located:
1061	in the weld metal
1063	in the HAZ
1064	in the main material
Group N 2 - Cavities
200	Cavity
Cavity
Hohiraum
201	Gas cavity	Cavity formed by trapped gas released during crystallization
Gas cavity

Source: http://docs.cntd.ru/document/464675360

What are the types of weld defects, classification by groups

When carrying out welding work, it is necessary to take all measures to increase the quality of the formed seam. The service life of the product depends on the degree of quality.

Defects in welding seams can occur under the influence of a number of factors, including such as non-compliance with technology, lack of necessary welder qualifications, negligence, and incorrect operation of equipment.

Depending on the degree of deviation of parameters from the norm, acceptable and unacceptable defects are distinguished. All standards are defined by GOST 30242-97.

This document is called “Defects in joints when welding metals.” First of all, it defines the concept of a defect. This term means a deviation from the indicators defined by GOST, technical specifications and project drawings.

Welding defects are divided into groups.

• The first group consists of cracks. This is a defect caused by a seam tear. A crack can occur when there is a sudden change in temperature or when exposed to mechanical stress.
• The cavities or pores have an arbitrary shape. Formed in molten metal when there are trapped gases in it.
• Solid inclusions are represented by foreign bodies that got into the molten metal during the formation of the weld.
• Lack of penetration and lack of fusion are defined as an unreliable connection between the weld metal and the base material or a complete absence thereof.
• Violations of the seam shape mean deviations from the accepted geometry, which is defined for the outer surfaces of the seam.
• Welding defects that do not fall into the listed groups.

According to this standard, each defect is indicated by a three-digit code or a four-digit number indicating its type.

For example, if a sag is marked with the number 509, then a sag in the horizontal plane, as its variety, is 5091.

Some defects have a letter designation. The procedure for their use has been agreed upon with the International Welding Institute. In this standardization, the crack is designated by the letter “E”, and the cavity by “A”.

Group 1. Cracks

Defects of type 100 or “E” are considered unacceptable. In the zone of crack formation, the structure will certainly collapse. The rupture occurs in the seam itself or in the immediate vicinity. When a crack occurs, the opening may be minimal, but the action of loads leads to rapid destruction. According to statistics, this type of defect appears when welding alloy and carbon steels. The risk of cracks increases when the weld cools quickly.

The reason for the formation of cracks is the presence of carbon, silicon, sulfur, nickel or hydrogen in the metal. If the technology is not followed, excessive stress occurs in the seam area. To eliminate cracks that have already formed, you must first drill their ends. Then the crack is removed by planing, and the place where it is located is cleaned and welded again.

Cracks can be classified by origin; they are divided into cold and hot.

• Cold cracks form after the seam has cooled, when the temperature is 300°C degrees. Such defects can manifest themselves after quite a long time. Phase transformations that occur during metal crystallization sharply reduce strength indicators. Atomic hydrogen does not completely evaporate and causes cracks to appear. This can only be avoided by ensuring protection of the weld pool.
• Hot cracks occur at high temperatures (1100-1300°C degrees). During crystallization, a process occurs that is the opposite of linear expansion. Pulling the metal together causes it to rupture. This type of crack is directed not only along the seam, but also across it. Discontinuities form at the boundaries of crystal grains.

Cracks can be divided by size. Macroscopic cracks (100; E) are assessed visually. Microcracks (1001) appear only when using magnifying devices. Often it is necessary to use fifty times magnification to observe the defect.

Group 2. Pores

Pores in metal are cavities that are filled with gas. They begin to form when the metal is in a liquid state. At this time, the process of gas formation is observed, but only some of the bubbles come out. The size of the cavity varies from micrometers to several millimeters. Sometimes entire clusters of pores are observed, forming shells. Usually the cavity has a round shape.

Pores can appear for a number of reasons. The first of them is the low quality of cleaning surfaces from contamination. Particles of rust, scale, and oil may remain on the edges. At high welding speeds, the gas simply does not have time to leave the liquid substance, remaining in it in the form of bubbles. As already noted, the tendency to form pores is especially pronounced when working with carbon steels.

Violation of welding technology will lead to negative consequences. Particular attention should be paid to climatic conditions. High humidity affects the state of the flux. The appearance of pores leads to the fact that after preliminary gouging the surfaces have to be cleaned and welding repeated.

The cavity (200; A) can be of any shape with rounded corners. The bubble contains hydrogen, nitrogen or carbon monoxide. Gradually the metal hardens and a pore forms. Often these two concepts are separated, since the pore has a spherical shape, and the cavity is irregular. But in this classification these defects are identical. A series of pores distributed evenly (2012) is a defect observed when working with non-ferrous metals. Its variety is a chain (2014) and a cluster of pores (2013).

A special case of a pore is a fistula (2016; Ab). The index shows that this is a defect of the same type, but the fistula is represented by a tubular cavity that penetrates the suture right through. The reason for its occurrence is high humidity. The shape of the fistula depends on the gas released. Sometimes a fistula occurs when the metal overheats or an accidental short circuit caused by contact of a tungsten electrode with the surface. Such a defect must be corrected by complete removal of the metal followed by overcooking.

A crater, marked as defect 2024 or “K,” forms a shell at one edge of the weld bead. Usually appears as a result of a sharp detachment of the electrode. If in appearance the crater does not have cracks, then upon closer examination they most often appear, so such a defect must be eliminated.

Crater formation is the result of inept welder actions.

Group 3. Solid inclusions

Foreign particles reduce the strength of the seam and act as localization sites for excessive stress. If solid inclusions are detected, gouge until healthy metal appears, and then repeat the welding process.

Defect 300, which consists in the entry of metal particles into the weld zone, in the presence of at least one acute angle, is called an acute inclusion.

An example of such a defect is a slag inclusion (301; Ba), a flux inclusion (302; G), an oxide inclusion (303; J) and a metal inclusion (304 H).

The slag inclusion is divided into linear (3011), isolated (3012) and others (3013). Slag, which is formed as a result of melting of an additive or flux, always floats to the top.

But if the technology for guiding the electrode is violated or at high welding speeds, it often remains inside the molten metal. For work in a protective gas environment, the phenomenon of slag inclusions is rare.

There are established standards for particle sizes at which the operation of a part is allowed. If this norm is exceeded, the seam is cut out and digested.

https://www.youtube.com/watch?v=1d13sKNHnTY

Flux inclusions are divided into the same types (3021, 3022 and 3023, respectively). They arise from flux residues that have not had time to react with the metal. It usually floats to the surface, but parts may remain inside, forming a defect.

A similar situation occurs when the flux is selected incorrectly. For example, if it is presented in the form of large granules. Excessive welding speed can also provoke the occurrence of inclusions.

Oxide inclusion is oxide trapped in the weld metal. It is formed as a result of the reaction of a metal with oxygen. The oxide film is refractory and difficult to dissolve, so when it appears, a defect is sure to form. To avoid the formation of a film, it is necessary to protect the welded zone with active or inert gases. Particular attention should also be paid to surface preparation. Oxide inclusions are usually located in the form of a layer in the massif, which leads to the destruction of the seam.

Metallic inclusions of tungsten (3041), copper (3042) and other elements (3043) can occur if the weld pool is not properly protected. In most cases, such defects can be observed during an accidental short circuit of the tungsten electrode. The situation can be recognized by the characteristic crackling sound and sharp arc flashes. Tungsten has a high melting point, so it does not dissolve in liquid metal.

Group 4. Lack of fusion and lack of penetration

A characteristic sign of non-fusion is a poor connection between the weld elements and the workpiece metal. Varieties of the defect are lack of fusion on the side (4011), between the rollers (4012) and at the end of the seam (4013). Defects such as lack of fusion are characteristic of arc welding. Its essence lies in the fact that the metal of the edge did not melt completely, so the joint turned out to be of poor quality.

This is often preceded by incorrect cutting of the edges or errors in choosing the position of the electrode. The situation is aggravated by the chemical heterogeneity of metals. The welder must accurately set all welding parameters (current strength, speed of weld formation).

Defect 402 or “D” - incomplete penetration. Lack of fusion is technically similar to lack of fusion. The difference is that in this type of technology violation, areas are observed where the metal was unable to penetrate the root of the connection. Lack of penetration can be observed between the base material and the weld metal, as well as between the layers of the weld in multi-layer welding. Lack of penetration is observed during double-sided welding in the middle of the section. You can notice the defect visually, because there is a crack at the end of the zone.

Lack of penetration can lead to a decrease in the strength of structures. Seams with lack of penetration are especially sensitive under vibration loads. Even small areas with a defect reduce performance by 40%. Lack of penetration of the root impairs the strength of the connection by 70%. As with non-fusion, in this case the reason lies in the incorrect choice of welding mode. A defect between layers occurs when surfaces are poorly processed. The defect is corrected by removing the seam and re-welding.

Group 5. Violation of the seam shape

Before performing welding work, preliminary design takes place, as a result of which the geometry of the future seam is established. Deviation of the shape from the established standards is qualified as defect 500. Violation of the shape of the seam not only negatively affects its strength, but also worsens the aesthetic appearance. Reasons include possible power surges, uneven wire feeding or incorrect electrode angle.

The most common defects of this type include various undercuts. They weaken the resistance of the structure to loads. Undercutting occurs when the current is exceeded or when the gas burner flame increases.

Modern semi-automatic machines allow you to control the welding mode, so recently undercuts have become much less common, however, if the welder is insufficiently qualified, this defect does occur.

Undercuts are corrected by reapplying a thread stitch. If aesthetics are lost, then the strength of the connection returns to normal. When working with thin sheets of metal, burns occur. Presence of burn-through (510). It is visually identified in the form of through holes and indicates that the welding current is set too high on the inverter. Elimination of burns involves cleaning the places where they are located and re-welding.

Group 6

All other defects that are not included in the previous groups are positioned as defects 600. These include random arcing, spattering, scuffing and reduction in metal thickness. Despite the wide variety of welding seam defects, very specific recommendations have been developed to prevent them.

It will be difficult for a novice welder to comply with all the requirements, but professional welders can easily avoid poor-quality results. It is necessary to initially develop a welding technique. To do this, it is necessary to resolve such issues as the choice of equipment, the choice of consumables, proper surface treatment, and welding techniques.

Source: https://svarkoy.ru/teoriya/defekty-svarnyx-shvov.html

What is undercutting in welding and 7 ways to prevent it

12.06.2019

A flaw called an undercut is a depression created near a seam. Due to a decrease in the thickness of the metal at the defect site, the strength of the welded joint decreases. Externally, undercuts look like shrinkage grooves along the entire length of the seam or in certain areas.

Causes

Most often, defects, called undercuts, are caused by inexperienced welders when choosing the wrong current. The following may also be the cause:

• poor wettability of metal workpieces;
• change in arc length when applying a weld;
• significant deviations of the electrode from the joint axis;
• inconvenient arrangement of workpieces for welding;
• poor quality edge preparation;
• overestimation of the speed of work;
• Incorrect electrode angle.

Methods to prevent weld undercuts

The risk of defects is minimized if the joint preparation is completed in full, and welding is carried out in compliance with technological rules:

1. To avoid undercutting the weld, the workpieces are preheated to improve wettability. This improves the spreading of liquid metal across the width of the joint and reduces the likelihood of the formation of hotspots.
2. If the electrode is not positioned correctly, defects appear due to uneven heating of the edges. When joining parts of different thicknesses, most of the heat is directed to the thick edge. Carbon steel is welded by tilting the electrode at an angle forward.
3. At increased welding speeds, the metal in the central part of the weld quickly cools, creating shrinkage grooves along the edges. However, reducing the speed too much does not solve the problem. Therefore, the optimal value is chosen in accordance with the brand of iron being welded.
4. The probability of the formation of flaws increases significantly if the shielding gas is chosen incorrectly. Carbon steel is welded in a mixture of inert and carbon dioxide. When working with other materials, the type of gas is selected depending on the type of metal being welded.
5. For inexperienced welders, defects most often appear when welding rules are violated. When the diameter of the electrode is smaller than the width of the seam, it is necessary to make transverse movements with a large amplitude. After such welding, the formation of undercuts is inevitable. Therefore, if possible, you need to reduce the width of the connection or weld it in several passes. To avoid overheating of the base metal, the operating current is set in accordance with the thickness of the workpieces. Welding is performed with a short arc at a constant speed.
6. When applying vertical seams, flaws are formed due to the difficulty of filling the joint space with molten metal. Therefore, the connection of workpieces, if possible, should be performed in a horizontal position with less consumption of electrodes. To prevent the formation of undercuts, fillet seams are applied using the “boat” method.
7. The best way to prevent undercuts is to create welded joints using inverters with MIG/MAG functions. In addition to shrinkage grooves, these devices allow you to avoid the appearance of other defects on welds.

Source: https://svarkaprosto.ru/tehnologii/podrez-svarnogo-shva

Typical welding defects and types of defects

Welding joints of metals makes it possible to obtain high-strength structures with a structurally integrated permanent contact zone. The process associated with local melting has its own characteristics, therefore [welding] is performed using a technology that does not allow deviations from the regime. Any violation in duration, temperature, or purity of the metal leads to the occurrence of defects.

The causes, descriptions and methods for eliminating welding defects are described in specialized literature and regulated in GOST 30242-97. The classification of defects involves division into three groups - external (surface), internal (structural) and through, passing through the entire thickness of the seam or parts of the joined fragments.

https://www.youtube.com/watch?v=ZbnEIr5ITFc

As they deepen, all types of welding defects are divided into main groups according to external signs and characteristic features:

• cracks;
• cavities, bubbles and pores in metal;
• the presence of solid foreign inclusions in the metal;
• lack of penetration and influx;
• lack of fusion of metal in the contact area;
• craters, irregularities, scars and other unclassified deviations from standards.

Any heterogeneity in the seam and adjacent areas of the metal causes a redistribution of forces, during which the strength of the connection and the durability of the seam are significantly reduced. In critical structures and loaded parts, this leads to a complete loss of properties.

External welding defects and weld defects

The main types of defects in a welded joint (seam) have a common origin - they are associated with the human factor. The reason for their occurrence lies in violation of the temperature regime, the use of faulty equipment, improper handling of metal, and negligence in preparation for welding. Often the incorrect choice of welding technology leads to the occurrence of a defect.

IMPORTANT TO KNOW: Using borax for brass soldering

Cracks after welding

They are distinguished by their occurrence depending on temperature changes and direction - cold and hot, longitudinal, transverse and radial in direction. Depending on the welding technology, the crack may have different depths. Hot ones arise when the metal is heated to 1100 - 1300 C.

Their appearance is associated with uneven temperature distribution and the resulting tension in the metal. Cold ones appear when the metal cools at about 120 C. Another reason is the presence of foreign substances, hydrogen atoms, in the original steel.

Cracks may appear during electric and [gas (acetylene) welding].

Welding undercut

Defects appear when the workpieces are heated unevenly, when part of the molten metal flows to the other side. Externally, the undercut looks like a groove between the main body of the part and the weld bead.

If the weld is fused unevenly, the undercut appears quickly, which leads to a decrease in the strength of the joint. The metal in the undercut zone has altered ductility. The weld undercut is eliminated by stripping the seam and overwelding.

The problem is common when using arc and TIG welding with insufficient arc voltage control.

IMPORTANT TO KNOW: Argon welding (argon arc) - technology and equipment

Welding bead

The defect is due to excessively slow welding and insufficient temperature control. When the metal is weakly heated, part of the molten mass flows onto one side, without creating sufficient adhesion with it. The sagging may be poorly visible upon inspection, but in most cases this is a place where the molten masses have not joined together, or metal has not fused. The seam may fall apart under minimal loads. If an influx is detected, it is removed mechanically and the seam is digested.

Welding crater

A defect can occur when the arc suddenly breaks or the supply of the [plasma jet] is stopped. A small depression at the end of the seam is usually associated with another defect - internal lack of penetration in a local area.

As the metal shrinks and cools, stress cracks may appear in the crater area, making the weld completely unusable. The crater is cleaned until completely leveled, and the area is digested.

It is often found at the ends of short welds when an unskilled welder abruptly breaks the arc.

Internal welding defect - fistula, lack of weld penetration, pores

Defects in internal welding joints include fistulas, lack of fusion and pores. External signs may not be enough to identify them. It is especially dangerous in the manufacture of loaded structures for the degeneration of pores into fistulas. This type of defect can be combined with lack of penetration when the specialist is dealing with large cross-section parts or deviation of the electrode from the axis of the seam. Lack of penetration usually has the effect of significantly reducing strength.

Pores and fistulas along the seam are formed when slag particles are introduced into the heating zone and gas bubbles appear. A crack will subsequently appear along the line of the fistula. The consequences of lack of penetration depend on the depth of the defect.

IMPORTANT TO KNOW: Plasma welding technology

Eliminate defects by cleaning and digesting. In the area of ​​lack of penetration, edges and contact surfaces should be carefully processed.

Burn through during welding

Pores and fistulas that pass through the entire thickness of the metal are classified as through defects. No less serious in consequences is welding burn-through of metal, which occurs when the temperature is exceeded, the arc is overexposed, or the incorrect assessment of the thickness of the steel. The cause of burn-through may be significant oxidation of the metal.

Basic methods for eliminating welding defects and defects.

The main methods for eliminating welding defects and joint defects are well known and are specified in GOSTs and TUs.

1. The welding method is suitable for large cracks, which are pre-drilled at the ends and cleaned.

2. Internal defects in the form of cracks and lack of fusion, including detected foreign particles, are removed by cutting and digestion.

3. To eliminate the undercut, welding of thin layers of metal or surfacing is allowed.

4. The nodules are cut down, cleaned off, and cut off depending on their hardness and size. Non-fusion in the influx zone is digested completely or layer by layer.

The appearance of external signs of a welding defect indicates that the structure of the metal at the point of contact is damaged. Without eliminating the defect, you get a real defect in the part and a fragile structure that will not last long.

Source: https://rezhemmetall.ru/tipichnye-svarochnye-defekty-i-vidy-braka.html

Defects in welded joints - types and methods for eliminating them

What are defects in welded joints? In essence, these are deviations from the requirements for the technical characteristics of the weld, and, accordingly, the entire structure. It is welding defects that reduce the strength of the seam and the reliability of welding joints. They can be divided into several types.

Types of weld defects:

• deviations from the size and shape of the seam;
• flaws in micro- and macrostructure;
• warping and deformation of structures.

Deviations from the dimensions of the seam and its shape

The dimensional parameters of the weld are determined by state standards. And each type of welding has its own GOST. For example, when welding, where the melting method is involved, weld defects are determined by the uneven filling of the groove being welded, plus the difference in the width and height of the seam along its entire length. As for the shape, it is uneven, there are so-called saddles (depressions), tubercles, its structure is scaly.

The reasons that occur during manual welding are low quality electrodes, low qualifications of the welder, and violation of welding technology. The reasons for automatic welding are voltage surges, the electrode feed angle is incorrectly selected, the filler wire slips in the feed mechanism, and so on.

If we talk about pressure welding, then its defects in welds are deep dents, uneven distribution of points along the weld, and displacement of the workpieces relative to each other can occur.

Shape defects include burns, undercuts, sagging and uncertified craters.

Surges

Typically, such defects in welding seams are formed when welding workpieces lying in a horizontal plane. And the welding process itself is performed from above. Sludge is solidified liquid metal in the form of tubercles that are formed at the moment the hot molten metal of the electrode comes into contact with the cold surface of the workpiece. The beads can be of different sizes: from small drops to large rows extending over a decent length of the weld.

The reasons for the appearance of sagging can be a high current supplied to the electrode, a long electric arc, tilting of the workpiece, or an incorrectly chosen angle of installation of the electrode. The result is cracks in the weld, lack of penetration and other defects.

This defect is a groove (indentation) in the weld, which is often formed when welding near the metal of the workpiece. The reasons may be high current and a long arc, which create overheating of the metal itself, as well as the welding filler. It is the high temperature condition that causes the edges of two workpieces to melt.

If corner joints are welded, then most often the reasons for undercutting are an incorrectly installed electrode, especially when there is a shift towards the vertically installed workpiece. In this case, overheating occurs precisely on the vertical wall of the joint, and this is where the undercut is formed.

But on the horizontal at this time an influx forms, because the metal begins to flow down.

When gas welding, undercuts can occur for only one reason - increased torch power. It should be noted that undercuts are a fairly serious weld defect. It leads to a weakening of the workpiece in thickness, and this is the primary reason for the destruction of the joint, and accordingly the entire welded structure.

Burns

The name itself already speaks for itself. Holes are formed at the welding site and in the metals being welded along the edges. Causes:

• large distance between workpieces;
• high current and powerful torch for fast welding;
• irregularly shaped edges, very pointed;
• long duration of the process in one place.

Most often, this type of defect occurs when thin sheets of metal are welded together, or when multilayer welding is carried out and the first layer is applied.

Craters

These are indentations in the weld. Usually this defect is formed when the arc breaks. Therefore, experienced welders try to immediately melt it. This is the easiest way to eliminate welding defects. When welding is carried out automatically, a crater usually appears at the exit of the seam, that is, on the exit strip.

There is a subtype of craters called shrinkage cavities. It is formed under the influence of metal shrinkage in the weld. The thing is that metal decreases in volume as it cools.

Macrostructure defects

These types of defects in welded joints can be identified by increasing the structure of the weld by 10 times. This type of defects includes cracks, lack of penetration, gas pores, and slag inclusions.

Pores form when the seam cools quickly. At the same time, the gas-forming elements located in his body do not have time to escape. This happens when the edges of the workpieces are covered with rust, stains of oil or paint, a flux with high humidity is used, the welding machine was incorrectly configured for current or gas, there is a high carbon content in the metals being welded, and so on.

The pores can be large or small, they can be located in a cluster or evenly along the seam, there are through pores called fistulas. In general, their number and size depend on the time during which the bath is in a liquid state. The longer the weld pool is liquid, the smaller the pores, because the gases have time to leave the liquid metal.

Slag inclusions are essentially negligence on the part of the welder when welding. This means that he poorly prepared the two metals being joined for welding. There was dirt and rust left on them. If this type of defect appears during multilayer welding, it means that the welder did a poor job of removing slag from the previous layers.

These defects can be several microns in size or several millimeters in size, and have different shapes: from a sphere to a thin line. Location - throughout the body of the seam.

Lack of penetration is a serious defect. It turns out that the metal of the workpiece is not fused with the metal of the electrode (electric welding) or filler wire (gas welding). The layer of deposited metal may not fuse with each other. There are many reasons for lack of penetration:

• too much current was used during welding;
• edge contamination;
• the electrode was brought incorrectly to the axis of the seam;
• very small gap between two workpieces;
• the edges have too pointed ends;
• forced break, during which the metals cool;
• increased welding speed.

As for cracks, they can be divided depending on the temperature at which they appear. That is, cold or hot. Hot ones appear when the metal hardens, and crystallization begins at a temperature of 1100-1300C.

At the same time, shrinkage stresses appear inside the weld metal, and semi-liquid layers begin to form. They subsequently become cracks.

If the deposited metal contains a lot of hydrogen, carbon or silicon, then this is also the cause of hot cracks.

Cold cracks form at temperatures of 100-300C. The reasons are the same stresses that arise in the body of the deposited metal when it begins to cool. In addition, hydrogen (gas) remains inside the weld, which tends to escape.

And this is additional stress. By the way, hot cracks on the front part of the seam are not visible, they are considered internal. But cold ones immediately appear on the outside of the seam and are clearly visible to the naked eye. These are external defects in welds and joints.

There are two more types of cracks: tempering and lamellar. The first ones are formed already when the welding is completed and the next metal processing operations are carried out. The latter have a very interesting technology of appearance. They are formed at high temperatures, but their further development occurs in the cooled metal. By the way, most often this type of defect is formed from microscopic cracks. Both options belong to the category – external defect.

Microstructure defects

Microstructure defects include microscopic cracks and pores, inclusions of non-metallic type (oxygen, nitride), coarse grain structure of the deposited metal with elements of overheating and burnout.

The most dangerous of all the listed defects is burnout. With it, large grains of the metal structure appear in large numbers inside the seam, which have minimal strength connections with each other. Hence the high fragility of the joint. The causes of burnout are the presence of oxygen in the welding zone, which means that the insulation of the bath was poor. Here you can add the high temperature of the welding process.

Acceptable and unacceptable defects

It is clear that all defects in welded joints negatively affect the quality of the welded structure. But there are those in which the structure can be operated without problems, and there are those in which its operation is strictly prohibited.

Therefore, before determining whether a welded structure can or cannot be used, it is necessary to take into account all the circumstances and factors influencing the choice.

• It is necessary to determine whether the design complies with all geometric and dimensional parameters strictly according to the project or drawing.
• Type of defect, its size and location in the connection.
• What mechanical loads will the building or structure be subjected to? Will their welding joints hold up?
• Nature of the environment. Natural loads negatively affect the condition of the weld.
• Functions assigned to the structure. That is, one defect can withstand certain loads, while others are contraindicated.

The admissibility of defects can only be determined using special equipment. Therefore, it is recommended to use equipment that, in terms of the degree of verification of the defect, was higher than the nominal permissible value of the defect itself. For example, a 3 mm crack cannot be measured with a device that detects minimum cracks of 5 mm in length.

By the way, admissibility is influenced not only by the size and shape of defects, but also by their number and frequency of location.

Conclusion on the topic

Defects in welded joints affect the quality of the joint between the elements of the assembled structure, and therefore the entire structure as a whole. Therefore, special attention is given to correcting welding defects. They cannot eliminate themselves.

There are flaws that can be easily eliminated, and there are those that can be eliminated, but not easily. Methods for eliminating them are known. And there are defects that cannot be corrected. So it’s better to carry out the process competently.

Therefore, study the processes of seam formation and the reasons for their formation.

Source: https://svarkalegko.com/tehonology/defekty-svarnyh-shvov.html

Defects in welding seams and the reasons for their formation

All deviations from technological parameters caused by negligence in work, violation of operating conditions and external causes, often beyond the control of the welder, can lead to defects in the weld seam and the weld zone falling into the thermally affected area. Defects can also be caused by violation of technological methods of both the welding process itself, and poor-quality preparation, equipment malfunction, deviations from the quality standards of welding materials, the influence of weather conditions, and low qualifications of the welder.

The occurrence of defects is often associated with metallurgical and thermal phenomena that occur during the formation of the weld pool and its crystallization (hot and cold cracks, pores, slag inclusions, etc.; These defects reduce the strength and reliability of the welded joint, its tightness and corrosion resistance. All this can have a significant impact on the operational capabilities of the entire structure and even cause its destruction.

Defects in welding seams can be external or internal.

External defects of welding seams

External defects in welds (Fig. 1) include violations of the size and shape of the seam, undercuts and other deviations that can be detected during an external inspection of the welded joint.

Violation of the shape and size of the weld is most often caused by voltage fluctuations in the electrical network, negligence in work or low qualifications of the welder, manifested in the wrong choice of modes, inaccurate direction of the electrode and the method of its movement.

Defects manifest themselves in unequal width of the weld along its length, uneven leg of fillet welds, excessive convexity and sharp transitions from the base metal to the deposited one. Deviations from the size and shape of the welded joint, which appear in fillet welds, are associated with improper preparation of the edges, uneven welding speed, as well as untimely control measurements of the seam.

In automatic and semi-automatic welding, these defects are most often associated with voltage fluctuations, wire slipping in the feed rollers, and violations of welding conditions.

Lack of penetration is a local lack of fusion between the elements being welded, between the base and deposited metal or individual layers of the weld in multilayer welding. The reasons for lack of penetration are poor preparation of the welded edges (scale, rust, small gap, excessive dullness, etc.), high welding speed, displacement of the electrode from the axis of the joint, insufficient current.

As a result of lack of penetration, the cross-section of the weld is reduced and local stress concentration occurs, which ultimately reduces the strength of the welded joint. Under vibration loads, even small lack of fusion can reduce the strength of the connection by up to 40%. Large lack of root penetration can reduce the strength by up to 70%.

Therefore, if the lack of penetration exceeds the permissible value, the seam section must be removed followed by overwelding.

Undercut is the most common defect found in welding. It is expressed as a depression along the line of fusion of the weld with the base metal. As a result of undercutting, a local decrease in the thickness of the base metal occurs, which leads to a decrease in strength. Undercutting is especially dangerous in cases where it is located perpendicular to the operating stresses.

Undercut usually occurs at increased arc voltage with increased welding speed, when one of the edges is melted deeper, liquid metal flows onto the horizontal plane and is not enough to fill the groove. When welding fillet welds, undercuts occur mainly due to the displacement of the electrode towards the vertical wall, which causes significant heating, melting and flow of the metal onto the horizontal shelf.

In butt welds, undercuts are formed when welding at high currents and when the filler material is incorrectly positioned. Increased cutting angles can lead to undercutting. This defect is detected visually and in case of deviations above the established norm, it must be overcooked with preliminary cleaning.

Short cuts that weaken the seam section by no more than 5% in structures operating under static loads can be considered acceptable. In endurance structures, undercuts are not allowed.

Sagging - manifests itself in the form of leakage of weld metal onto the surface of the base metal without fusion with it. Sagging sharply changes the outline of the seams and thereby reduces the endurance of the structure.

The cause of this defect may be reduced arc voltage, the presence of scale on the edges being welded, or slow welding when excess molten filler metal appears. Most often, sagging occurs when welding horizontal seams on a vertical plane.

When welding circular rotary joints, sagging can occur if the electrode is incorrectly positioned relative to the axis of the seam. Long surges are unacceptable.

Burn-through - penetration usually occurs due to high current at low welding speed. It appears in the form of a through hole in the weld, which occurs as a result of leakage of the weld pool. In multilayer welding, burn-through occurs during the first pass of the seam.

The causes of burn-through can be an excessive gap between the welded edges, insufficient thickness of the lining or its loose fit to the base metal, which creates the precondition for leakage of the weld pool. Burn-through can occur when the supply of shielding gas suddenly stops. When welding rotary annular joints, burns are caused by incorrect location of the electrode relative to the zenith.

The defect is detected visually and is digested after preliminary cleaning. Burns are caused by liquid metal entering areas outside the weld.

An unwelded crater is a weld defect that forms in the form of depressions in places where the arc is abruptly torn off at the end of welding. Shrinkage looseness may appear in the recesses of the crater, often turning into cracks.

Craters are usually caused by improper welding practices. During automatic welding, a crater may appear in the areas of the lead strips where the weld seam breaks. Craters are often the cause of crack development and are therefore unacceptable.

They are cleaned and brewed.

Surface oxidation is scale or a film of oxides on the surface of a welded joint. Surface oxidation depends on poor protection of the weld pool, the quality of preparation of the welded edges, improper adjustment of the supply of shielding gas, its composition, and large electrode overhang.

A fistula is a funnel-shaped depression in a weld seam, developing from a shell or large pore. The reason for the development of a fistula is most often poor preparation of the surface and filler wire for welding. The defect is detected visually and must be overcooked.

Rice. 1 External defects of welds, revealed by external inspection: A - undercut; B - influx; B - burn; G - unsealed crater; D—fistula.

Rice. 2. Cracks in the weld and heat-affected zone: A - longitudinal hot crack; B - cold crack in the heat-affected zone.

Internal weld defects

Cracks can be cold or hot (Fig. 2). Cracks can be both external and internal. These are the most dangerous defects in a welded joint, often leading to its destruction. They appear in the form of a gap in the weld or in areas adjacent to it.

At first, cracks form with a very small opening, but under the influence of stress their propagation can be commensurate with the speed of sound, resulting in the destruction of the structure. The reasons for the formation of cracks are high stresses arising during welding.

Most often, cracks appear when welding high-carbon and alloy steels as a result of rapid cooling of the weld pool. The likelihood of cracks increasing when the parts being welded are rigidly fastened.

Hot cracks - appear during the crystallization of metal at temperatures of 1100-1300°C due to a sharp decrease in plastic properties and the development of tensile deformations. Hot cracks appear at the grain boundaries of the crystal lattice.

  The appearance of hot cracks is promoted by an increased content of carbon, silicon, hydrogen, nickel, sulfur and phosphorus in the weld metal. Hot cracks can occur both in the weld mass and in the heat-affected zone. Hot cracks can propagate both along and across the seam.

They can be internal or come to the surface.

Cold cracks - occur at temperatures below 120°C, that is, immediately after the weld has cooled. In addition, cold cracks can occur after a long period of time.

The reason for the appearance of cold cracks is welding stresses arising during phase transformations, leading to a decrease in the strength properties of the metal. The cause of cold cracks may be dissolved atomic hydrogen that did not have time to be released during welding.

The reasons for the ingress of hydrogen may be undried seams or welding materials, or violations of the weld pool protection.

Pores are cavities inside the seam, filled with gas that has not yet escaped (primarily hydrogen). They can be round or elongated, and their sizes depend on the size of the bubbles of the formed gases. Pores can be single or develop in a chain along the weld seam.

The main reasons for the appearance of pores are: the presence of harmful impurities in the base or filler metals, rust or other contaminants that are not removed from the welded edges before welding. Increased carbon content also contributes to the appearance of pores. Pores can appear when the protection of the weld pool is violated or the welding speed is increased. The main reason for the appearance of pores when welding with a consumable electrode is a damp coating.

Single pores are not dangerous, but their chain affects the strength of the welded joint. The area of ​​the weld seam in which pores are present must be rewelded by preliminary mechanical cleaning.

Slag inclusions are weld defects, expressed in the presence of cavities filled with slag that has not had time to float.

The formation of slag inclusions occurs due to poor preparation of welded edges and filler material, excessive welding speed or poor protection of the weld pool. When welding in shielding gases, slag inclusions are rare.

Slag inclusions can be up to several tens of millimeters in size and are therefore very dangerous. The section of the seam where slag inclusions exceed the permissible standards is subject to cutting and rewelding.

Tungsten inclusions - occur when the protection of the weld pool is violated when welding with a non-consumable tungsten electrode. In addition, tungsten inclusions occur during short circuits or excessive current density. Tungsten inclusions are especially common when welding aluminum and its alloys, in which tungsten is insoluble.

Oxide inclusions are formed as a result of the formation of poorly soluble refractory films. Most often they occur due to significant surface contamination or violations of the weld pool protection. Being an interlayer in the weld mass, oxide inclusions sharply reduce the strength of the welded joint and can lead to its destruction under the load applied during operation.

Source: http://build.novosibdom.ru/node/287

Weld undercut and 7 ways to prevent it

Defects in welding joints often complicate our lives. A weld undercut or shrink groove is a flaw characterized by the formation of a groove near the root of a single-sided weld due to overheating of the base or weld metal (fusion edge shrinkage).

This occurs when the welder tries to weld with high welding voltage or at a fast welding speed. Additionally, an incorrect angle directs the arc toward thinner edges where overheating can burn the metal.

Such a defect in welding joints can be caused by improper use of a protective gas atmosphere, violation of welding technique, position of the item being welded, etc.

Shrinkage grooves have always been a serious problem in the welding and steel processing industries. Efforts have been made to solve this problem in recent years. Below are tips that can effectively help prevent or reduce the frequency of this phenomenon.

Appropriate heating

Undercutting of a weld seam is most often caused by high heat sources that arise after passing near the edges. This can lead to overheating and melting near the root of the weld. To prevent defects, great care must be taken when welding metals by reducing the current when approaching thinner, looser edges.

Electrode position during welding. Correct angle

An incorrect angle during welding often plays a particularly important role in the occurrence of defects of this kind. Even one pass with an incorrect angle, which directs more heat to the free edges, makes the weld prone to shrink grooves. To avoid problems, you just need to use the right angles to direct more heat towards the thicker components compared to the free edges.

Moderate welding speed

Making a weld with a high melting rate is another big cause of edge shrinkage. This forces some of the original base metal into the bottom center of the weld puddle and, due to rapid solidification, leaves an indentation along the edges. It is recommended to carry out welding work at a moderate pace. Do not forget: a slow speed will also negatively affect the result of the work and will not give satisfactory results.

Correct choice of shielding gas

In the case of MAG (Metal Active Gas) welding, the incorrect choice of shielding gas can be one of the main reasons for the appearance of undercut welds. The correct gas composition in accordance with the requirements for the type of material and its thickness will ensure a good result. When welding carbon steels, it is best to use carbon dioxide in combination with inert gases.

Correct welding technology

Weld undercut or shrink grooves often occur when a welder attempts to make a weld with excessive lateral movement of the electrode during welding.

Codes and standards require recommended suture widths based on electrode size. The size of the seam when welding should not be more than an acceptable limit, otherwise the seam may be prone to undercutting.

In order to prevent this, you need to strive to either reduce the size of the suture area or make multi-pass seams.

Correct position of an object in space

Some welders try to make fillet welds not in a horizontal position, but in a vertical position, which promotes shrinkage at the edges. In this case, depressed forms are formed due to insufficient filling of the joint edges with metal. To prevent, if possible, try to brew in a horizontal position to ensure adequate electrode consumption.

Using multifunctional welding systems

The use of multifunctional MIG/MAG welding machines takes into account the above-mentioned warnings and allows the production of thin welds with improved mechanical properties. Thus, weld undercutting is best prevented by this method. By following all these rules, the welder minimizes the likelihood of negative consequences and defects in welds of this kind, in extreme cases, will be minimal.

Source: https://blog.svarcom.net/materials/podrez-svarnogo-shva.html

Methods for correcting welding defects (errors): how to correct the problem

Defects in the weld joint lead to deterioration in its performance and visual characteristics. To detect connection defects, there are different methods for monitoring the quality of the work performed.

This could be as simple as inspecting a welded joint. Or more complex testing techniques: x-rays, equipment using ultrasonic waves.

What can be done if seam defects are detected? Is the part recycled? No. If the inspection reveals defects in the welding joints, they can be corrected.

This article will discuss in detail the options for welding defects and how they are corrected.

Types of welding errors

Defects in welds are divided into two types: external and internal. Their names reflect the essence of these concepts. External flaws are on the joint surface.

They are detected without additional devices, by simple inspection. The internal type of welding defects is not externally noticeable.

Such flaws are found within the connection. Additional equipment is needed to detect and correct them.

Lack of penetration

Such external defects appear when the welding equipment is set to a low current level. When this indicator is underestimated, the effect of current is not enough to completely weld the joint.

https://www.youtube.com/watch?v=qBf24cIxYuU

Also, lack of penetration can occur at an increased speed of welding parts. In this case, the metal simply does not have time to boil thoroughly. Another reason may be inept cutting of the edges of the future joint.

To prevent this welding defect, a correctly set amperage and optimal welding arc length are sufficient.

Undercuts

This flaw is typical for T-seams and overlapping work. It is rare in butt welding. It appears when the arc voltage is incorrectly set and the welding speed is abnormal.

Preventing undercuts is quite easy. When welding, the welding arc voltage decreases and the work speed is normalized. For an accurate result, it is worth cooking with a short arc length.

It forms a fairly thin sheet, thanks to which the welding heat input is normalized. This protects against undercuts.

Hot or cold cracks

Hot cracking is caused by using the wrong type of filler rod. The metals of the part and the electrode must be compatible.

For example, you cannot weld stainless steel with an aluminum rod. These metals have completely different characteristics. Aluminum simply cannot cook stainless steel efficiently, and therefore cracks will appear.

The second reason may be an incorrect attempt to seal the crater. If, when correcting this defect, the impact is abruptly interrupted, the seam may crack.

Cold cracks appear after the seam has cooled. If it is made poorly, then when it hardens, the canvas may burst. Or if the connection is subjected to a mechanical load exceeding its resistance level.

This type of defects can also appear on the surface of the canvas, which partially refers to it as external defects.

Pores

Joint porosity is quite common. Pores inside the weld body can form when the working area is poorly protected from oxygen exposure, or the metal preparation stage is ignored or carried out incorrectly.

If there is rust left on the edges of the joint, there are any inclusions that disrupt the uniformity of the seam. Like cracks, pores can be an internal or external problem.

To avoid the appearance of porosity in the seam, you need to make sure that the supply of protective gas is configured correctly and protect the working area from external influences that could disrupt the protective cocoon (drafts, gusts of wind).

And also carry out the preparatory stage correctly.

Correction options

Now let's look at options for correcting defective connections that could not be prevented.

Large cracks are simply welded over. In order to prevent the crack from growing, holes are needed at its ends. The distance from the end of the crack to the hole is 0.5 mm.

After this, the crack is divided so that it looks like the letters V or X. To do this, cutters or a pneumatic chisel are used. After cutting, the crack is cleaned and welded.

Sometimes it is possible to warm up the defect before it is corrected. Then the surface of the weld and the place of treatment will be close in temperature, and stress will disappear from the ends of the crack. This way you can correct the external type of cracks.

When a seam has been rejected by internal cracks, lack of penetration or burn-throughs, the defective area is cut out (melted out), and a new seam is applied. The deposits are removed with abrasive materials (sandpaper, file).

If a part is deformed during adjustment, there are two solutions: mechanical and thermal.

In the first case, the deformation is removed by mechanical action on the part. Press straightening, spot blows of a hammer or a jack are used.

This is a difficult task that requires a lot of work. Often this method of correction leads to the appearance of other flaws, such as new cracks or chips.

To correct deformation thermally, the part is heated to a state of plasticity and allowed to cool again. The reverse stress that arises in this case neutralizes the deformation.

This method of correction is used more often than mechanical due to its simplicity and protection from additional problems.

The appearance of defects in the weld seam is based on a violation of the metal processing process. By knowing what violations lead to connection defects, they can be prevented. First of all, this is the level of qualification of the employee.

It must match the complexity of the welding. During work, the technology of the welding process and RDS must be observed. The device must be correctly configured and have high-quality, appropriately selected parts.

They must correspond to the chemical and physical properties of the metal being processed. If you choose the right tools and approach the welding process responsibly, the seam will be free of flaws and shortcomings.

Conclusion

Damaged parts should be rejected and sent for recycling. But if necessary, you can resort to correction.

It is possible to correct mistakes made during operation, but this will require time, knowledge and experience.

There are different types of welding defects and different actions are taken to correct them. The correction method is selected for a specific case. But if the seam has many flaws, the part should simply be disposed of.

At the beginning of the welding journey, beginners often make mistakes. This is normal because welding is a matter of experience. With effort, the seams will improve over time.

Source: https://prosvarku.info/tehnika-svarki/sposoby-ispravleniya-svarochnogo-shva

Weld undercuts – Osvarke.No

An undercut is a longitudinal depression on the outer surface of the weld bead. There are undercuts of continuous length (5011), which extend along the entire length of the seam bead, as well as alternating local ones (5012) in the form of undercuts in individual sections of the seam bead (in the second figure).

An unacceptable defect due to a reduction in the cross-section of the weld at the junction of the weld to the base metal, as well as stress concentration at the point of undercut.

External signs: a small depression throughout the entire seam or part of it along the line of fusion of the weld metal with the base metal.

Emergence process

The molten metal of the weld pool is forced into the central part. Low wettability and high crystallization rate do not allow the metal to spread within the fusion boundary.

Prevention methods

Before welding:

• improve the wettability of liquid metal by preheating the base metal;
• selection of optimal welding modes;
• use auxiliary devices to position and orient the welded joint in a position convenient for the welder;
• use welding materials that improve melt wettability.

During welding:

• perform short arc welding at optimal speed;
• weld fillet welds using the “boat” method;
• weld with an inclined electrode at an angle forward;
• accurately orient the electrode along the axis of the seam and its length;
• Use inverter arc power supply.

Remedy

The place where the undercut occurs is cleaned and the seam is welded.

Save:

Source: http://osvarke.net/defecty/podrezy/

Types of weld defects and methods for their elimination

There are several types of defects - external and internal . External defects are those that can be detected visually when inspecting the weld seam.

Internal defects, on the contrary, are located inside the welded joints and can only be seen after flaw detection, including x-rays and mechanical processing.

Defects can be acceptable or unacceptable , depending on the requirements for welding joints and the structure as a whole.

However, based on the definition itself, any defects are defects and require their complete elimination or minimization of their number and size.

Since weld defects are a cause that risks compromising the stability of the joint and the functionality of the welded structure, there are a number of operations to eliminate them. To minimize the likelihood of defects occurring, be sure to consider:

• 1) Welding technology and welder qualifications
• 2) Filler material and metal being welded
• 3) Surface preparation for welding and shielding gas
• 4) Modes and welding equipment

External defects

External defects include violations of geometric dimensions ( undercuts , sagging ), lack of penetration and burns , and unwelded craters .

The main cause of lack of penetration is insufficient welding current, since it has a greater effect on penetration into the metal.

Elimination of defects of this type usually occurs by increasing the power of the welding arc, reducing the length of the arc and increasing its dynamics.

Also, the cause of lack of penetration may be a high welding speed or insufficient preparation of the edges of the welded joint.

Lack of penetration can be of several types:

• - when the welding seam does not penetrate the entire thickness of the metal during one-sided welding (see the upper part in the figure)
• - when double-sided butt welding, the seams do not fit together, forming a lack of fusion between themselves (see the lower part in the figure)
• — when welding into a tee, the weld seam does not penetrate deep, but only clings to the edges being welded

Also, the cause of lack of penetration may be a high welding speed or insufficient preparation of the edges of the welded joint.

An undercut is a defect in the form of a groove in the base metal along the edges of the weld.

This is the most common defect when welding T-joints or lap joints, but can also occur when welding butt joints. This type of defect is usually caused by incorrectly selected parameters, especially welding speed and arc voltage.

When fillet welding (for example, when welding long seams when welding beams), undercuts often occur due to the fact that the welding arc is directed more towards a vertical surface.

Molten metal flows down to the bottom edge and is not enough to fill the groove.

If the welding speed is too high and the voltage is too high, the weld seam is formed “humpbacked”. Due to the rapid solidification of the weld pool, undercuts are also formed in this case. Reducing the welding speed gradually reduces the size of the undercut and ultimately eliminates this defect.

The length of the welding arc also affects the undercuts. If the welding arc is too long, the width of the seam increases, thereby increasing the amount of molten base metal. Since the heat input remains the same as the arc length increases, it is not enough for the entire welding seam, the edges quickly cool, forming undercuts. Reducing the arc length not only eliminates undercuts, but also increases penetration and eliminates defects such as lack of fusion.

This defect appears as a result of filler material flowing onto the base metal without forming fusion with it. Usually the cause of this defect is incorrectly selected welding modes and scale on the welded surface. Selecting the correct mode (matching the welding current with the feed rate of the filler material, increasing the arc voltage) and preliminary cleaning of the edges eliminates the appearance of sagging.

This defect is a hole through the weld. The main causes of burn-through are high current, slow welding speed or a large gap between the edges of the welded joint. As a result, metal burns through and the weld pool leaks.

Reducing the welding current, increasing the welding speed and appropriate preparation of the edge geometry can eliminate burn-through. Burn-through is a very common defect in aluminum welding due to its low melting point and high thermal conductivity.

A crater appears at the end of a weld as a result of a sudden break in the arc. It looks like a funnel in the middle of the weld when it is completed. Modern welding equipment has special programs for crater filling. They allow the end of welding to be completed at lower currents, as a result of which the crater is sealed.