Welding defects

Welding defects

Introduction

Such materials and metal forming and welding metallurgical terms of donor and recipient must have appropriate characteristics , so welding should be considered in terms of metallurgical physical metallurgy and welding two pieces of functionality that you specify ? The ability of metallurgy , who created the piece , in terms of mechanical function and healthy ? Can you facility for specific requirements, the welding machine to create a gas and the assumption of power generated at high temperatures or low temperatures may be hitting ? Standards because of the mechanical and industrial engineering and welding must be adhered to in all cases without fracture porosity and penetration weld slag , etc. should be done . Repetition of specialized welding , and in principle to all types of welding, welding can be should be the exact metals . Intermediate materials and electrode welding powder , must be careful enough . The environment before and during welding , and after welding as in the case of iron, should be created. 

An overlay ( accumulation weld edges ) overlap or over - roll

Defect along the weld root due to the flow of metal on the base metal surface occurs Ray without melting and welding it occurs.
Cause

One . Moving cancer than the normal or natural

Two . Improper electrode angle.

Three . Large-diameter electrode

4 . Very low amperage
Results

These factors are something like a cut edge and a stress concentration zone of the weld metal composition does not induced .

Burn or cut edge of the weld Underecut

Furrow along the edges of the weld surface welds or weld metal that has already been caused .

Cause

One . Amp high

Two . High arc length

Three . High sinuosity electrode

4 . Moving at very high speed welding

5 . Electrodes is very oriented to the angle connection .

6 . Slag with high viscosity
Results

These factors led to a focus area and an area prone to fatigue cracks .

Khalhay Slag Slag inclusion

The non-metallic materials which are caused by a welding slag Khalhay say , these inclusions can create weak spots in the weld deposit .
Cause

One . Slag is not properly cleaned from the previous joint

Two . Insufficient amperage

Three . Angle or improper electrode size

4 . Preparation of false
Results

Khalhay slag welding reduce the strength of the cross-sectional area prone to leave an offer .

Partial melting L.O.F Lack of fusion

The lack of connection between the weld metal and the base metal or between weld passes
Cause

One . Use small electrodes thick cold steel

Two . Insufficient amperage

Three . Improper electrode angle.

4 . Very high speed Motion

5 . Dirty surface ( metal shell , stain , oil , etc.)
Results

Remains weak weld joint to become an area prone to fatigue .

Porosity Porosity


BAE hole or porosity in the weld can be seen that both domestic and foreign . The porosity of the electrode can be wet or broken electrodes coated on base metal impurities occurs. Also named ( Mac tube ) , ( MAC level ) and ( Karami holes ) is also known .
Other causes

One . Base metal surface contamination such as oil pollution , dust , stains , or rust

Two . Wet coated electrode

Three . Insufficient gas shielded arc

4 . Base metals with high amounts of sulfur and phosphorus

Results

Greatly reduces the strength of the weld joint . Corrosive atmosphere , surface porosity to allow the weld metal attack and cause it to malfunction .

Welded joints are not aligned Join misagnment

This is usually not aligned and coplanar segments that are fused together are called . Non- alignment is a common problem in the butt preparation methods occurs when the root pages and pages linking to its proper place in the base metal for welding have not been .

Cause

One . Improper assembly of parts that must be boiling .

Two . Insufficient welds that breaks or fish tattoo is insufficient to cause motion .
Results

Being consistent is serious because the melting edge of the defect root cause of the stress concentration at the service cause premature fatigue failure of the connection .

Incomplete penetration L.O.P Lack of pentertation

Lack of full penetration weld root connection
Cause

One . Very low amps

Two . Root space is insufficient

Three . Large-diameter electrode

4 . High -speed motion
Results

Boil rapidly weakens and becomes prone to fatigue .

Leave Weld Weld cracking

Different types of connectors may not fit into the weld or heat affected zones occur. Welds may contain porosity, slag Khalhay or types are Turks . Khalhay porosity in the weld slag may be acceptable to some extent, but never cracks in the welds are not acceptable . Cracks in the weld or near the weld , this is an indication that there is definitely a problem during operation . Turks examination to determine the cause and ways to prevent them Ajad makes them for us . First, we must consider that we distinguish between crack and break . To our left , a phenomenon that is a result of factors such as freezing , cooling and internal stresses due to shrinkage of the weld is created . Hot cracks , cracks can occur at high temperatures and are usually linked to freezing . Cracks are cracks after being cooled to room temperature reaches the boiling occur and may even be the HAZ interface . Most of the physical stresses caused by shrinkage cracks that often stretch or change shape when an object is accompanied by cold welding occurs , are built, the contraction is limited by the physical stresses, strain, internal stress that this is only give rise to residual waste , leading to cracks are. In fact , there are two opposing forces :

One . Tension is created by the contraction .

Two . Strength and hardness of the base metal

Stresses induced contraction by increasing the volume contraction of the metal has been under increased . Large-scale processes influence rash and muscle strains increase . The tensions caused by muscle strains caused by increasing the strength of the filler metal and the base metal increases. YS also increased when the residual stress increases .

One . Welding necessary

Two . Preheat

Three . Temperature between pulses

4 . Heat treatment after welding

5 . Design Connection

6 . Welding methods.


7 . Filling
Leaving the center line

Leaving the center line in the center of a weld pass is given . If you have acne Kpas terminal and then connect Aynpalydrmrkz This appointment will also Trkmrkzy in Mrkzatsal . In the case that multiple passes through each layer, there's a few more left of center Hndsyb may not be connected at the center . From what is often seen in Mrkzatsal . Leave due to one of the following three phenomena :

One . Turkish is caused by separation and segregation .

Two . Turkish is the shape of the weld bead .

Three . Turkish is the surface changes .

Unfortunately, all three of these phenomena manifest themselves in the form of a kind and they are difficult to distinguish withdrawal . Furthermore , experience has shown that often 2 or even 3 of these phenomena interact with each other and influence the cracks . Indeed, understanding the basic mechanism of each type of central Turks to help us to seek a solution to eliminate the need to leave .
Head left from the separation

These cracks occur when the compounds with low melting point such as phosphorus, zinc , copper and sulfur segregate themselves at certain points during the cooling process . During the freezing process , compounds with low melting point molten metal is forced into the central regions because of their connection to the last compounds that will start freezing and boiling in these areas tend to increase segregation and separation . High levels of manganese in welding electrodes used to be able to overcome the low melting point of iron sulfide formation . Unfortunately, this concept of non -volatile substances other than sulfur can not be used .


Leave the center of the weld bead

The second type of leave Central

Acne is caused by leaving the pulse shape , the cracks penetrate deep into the processes that are associated with processes such as FCAW, SAW is observed under CO2 shielding . When pulse welding , a more in depth than digest welding ( cross-section view of the device). To remove this type of leave, the pulse width must be at least equal to the depth of the weld is. It is recommended that the weld width to depth ratio equal to 1 to 14/1 to be the first to leave these be overcome . If you are using multiple pulses per pass Nbt width to its depth , the weld without leaving a will . When a central steam leaving the pass is under study , the only solution is to change the depth to width ratio of the weld . This may be involves the design changes have connections . Since the penetration depth is a function of the weld may be useful in order to reduce the influence of the electrodes with diameters above we can lower the Mprhay . These solutions reduce the current density and penetration rate limits .


Leave the center of the weld surface conditions

Last mechanisms that cause changes in surface conditions is left of center . When the rash is caused by the concave surface of the internal stresses from contraction causes the acne is gone . Conversely , when the weld surface is convex inner force of contraction causes the weld surface is pressed . Concave weld surface , is often caused by high voltage arc . Slightly reducing the arc voltage causes the deformation of the weld convexity and leaving the state to be removed . High velocities may also contribute to this reduction in travel speed welding, the dispersion increases by welding and weld the convex surface of the switch . Welding in vertical down the cause of this type of leave . Vertical upward welding mode can prevent the occurrence of this type of leave .
Leave the area affected by acne

Leave weld -affected zone (HAZ)

Detachment occurs is determined by the immediately adjacent weld , although this type of welding process is left is Turkish however , occurs at the base , not the weld itself . The left one adjacent to the weld , leaving deserted corner or also called latency . Because the left after the steel temperature is Freezing f 400 , also called freeze- out occurs because the hydrogen is combined with hydrogen , also called withdrawal . In order for HAZ cracks occur simultaneously three conditions must be established :

One . Should there be a sufficient amount of hydrogen .

Two . Welding must be sufficiently permeable .

Three . Should there be enough residual internal stresses . Delete one of the above three conditions that usually cause these cracks disappear. In welding, a way to remove this type of leave is two or three variables ( the permeable electrode welding ) to limit . Hydrogen can be imported from various sources was boiling . Moisture and organic compounds are the main sources of hydrogen in the weld . Hydrogen can be used in steel electrode, the electrode and the atmosphere there is Trkyybat robes .

Transverse cracks

Leave a transverse crack is also called a crossover . Turkish in the direction perpendicular to the weld is created . This type of leave is of a kind that is often faced with the welding and weld strength is usually higher than the base metal is seen . This type of leave can be combined with hydrogen to leave the area affected by the weld HAZ was described earlier due to the high amount of hydrogen is sensitive to residual stresses and microstructures . The main difference between the two is that the left transverse cracks in the weld metal is the result of longitudinal residual stresses . If the pass is the contraction of longitudinally welded metal base against the resistance force , and in fact with the density and compressibility . Base metal adjacent to the weld strength is in compression due to the contraction of resistance welding and weld in compression limits . Because the base metal to cause conflict , tension develops in the weld length . , When faced with transverse cracks the surface of the electrodes , hydrogen and storage conditions should be considered . In the case of transverse cracks , reducing the strength of the weld metal is usually one of the solutions to eliminate these types of leave . There is an emphasis on the weld filler metal, weld deposits that alone may be lower strength and soft metal under normal conditions . However, the effect of alloying elements in the weld strength and ductility goes up, it could be reduced. Use a rash with lower strength , a solution can be effective in reducing the transverse cracks , the strength of the welding conditions are consistent with the defined standards .

Complexity

Complexity or extent in all types of welding distortion exists in many cases is so small that it is barely visible , but in some cases before welding distortion that occurs subsequently noted. Study the distortion is very complex , and what follows is a summary of causes metal distortion when under load, strain , or deformation that moves under load in elastic metals remain weak . ( Return to its original shape after the load was removed or formed ) which is known as the elastic range . Under high load , the metals are somewhat stressed that the other one does not return the form or do not form and the point ( yield point ) is called ( yield stress ). Metals by heating are expanding and contracting when they are cold , during welding metals are heated and cooled , causing high stresses are sharp and distortion . If the high tension of the elastic limit and the yield point of the pass are rejected , some permanent complications arise in metal , metal stress is reduced at high temperatures . Unwanted distortion caused by expansion and contraction of the metal is heated .


Types of Complexity

There are three main types of complexity :

One . Angular

Two . Longitudinal

Three . Transverse

The complexity of the control can be carried out in three steps :

* Before welding
* During welding
* After welding

Before the complexity of controlling the welding is performed by the following methods :

One . Herpes breakouts

Two . Clips , clamps and retainers

Three . Full and continuous reheating

4 . Raw assembly

After welding distortion control :

One . Slow cooling

Two . Body flame ( reverse heating )

Three . Annealing

4 . Détente

5 . Normalize

6 . Body Mechanical

The building structures more commonly applied methods 1 and 2 , and other methods are used in industrial work .
Annealing

It is a process of heat treatment to soften metal machining is used for the whole or cold , or the final piece usually critical temperature furnace ( for steel with 0.52% carbon, about C 820 - 723) is heat , cold and then slowly it is .
Détente

Welded parts , uniform heating to temperatures below the critical temperature , which is followed by slow cooling , this process reduces the yield point of the metal , thus decreasing the stress remains in a piece .
Normalize


Process for fine grain structure of the metal , which enhances its resistance to shock and fatigue. Above a critical temperature to the normal boiling components (C 820 for carbon steel with 0.25% ( approximately one hour per nm 25 thick heat is obtained and then cooled in air ( direct labor ).