Welding Techniques

11 Most Familiar Types of Welding Defects|Causes & Remedies

What is Welding Defect?

Welding defect can be defined as “The Irregularities formed in the weld metal due to wrong welding process, incorrect welding patterns, incorrect welding parameters or incorrect combinations of filler and parent metal”.

Any irregularity/discontinuity when surpasses some specific code limit in the weld metal then is termed as “Welding Defect”. Discontinuity/irregularity is termed as defect only when it exceeds some specific code limitations. As a result we can conclude that every defect is a discontinuity but every discontinuity can not be termed as defect. 

Defects are so common that they are parts of any kind of manufacturing. Welding defects can produce different kinds of variations from the desired welded bead shape, expected quality, size & technical requirements.

Welding defects may be visible on the surface or hidden inside the weld metal. Different kinds of crack are acceptable within permissible limits while CRACKis the only defect that is not accepted at all.

Percentage Division of Welding Defects

Welding defects causes have been broken down according to “American Society of Mechanical Engineering” as

  • Poor Process conditions 41%
  • Percent Operator error 32%
  • Wrong Technique 12%
  • Incorrect consumables 10%
  • Bad weld grooves 5%

Action Needed for the Presence of Welding Defect

If a welding defect is detected then the following list of precautions can be taken to remove or reduce the chances of occurring of defects.

  • If a defect is detected in a weld then it should be temporarily rejected & put on HOLD.
  • One should look for the cause and try to use a corrective action to avoid its repetition in the future.
  • An authorized professional should be consulted to find out whether the defect is repairable or not if it is then with the help of which procedures Standard procedures are approved for routine applications.

Standards Used for Evaluation of Welding Defects

All discontinuities in welding are not defects. Discontinuities are acceptable if they fall under a specified limit.

Keep in mind, acceptance standards may vary with requirement of services.

Radio-graphic standards are used for the evaluation of weld defects which are given below.



IIW consists of the following 5 standards

  1. Black
  2. Blue
  3. Green
  4. Brown
  5. Red


ASTM consists of following standards according to ASTM E-390 Vol-II

  1. Crack/Shrinkage
  2. Lack of fusion
  3. Burn through
  4. Elongated Porosity
  1. Slag inclusion up to level-III
  2. Incomplete Penetration up to level-II
  3. Undercut up to level- IV
  4. Porosity
    >Cluster porosity up to level-III
    >Fine Scattered porosity up to level-IV
    >Coarse scattered porosity up to level-II

How Defects Put an Impact?

If welding defects are ignored they can become a serious threat. Defects can result in failure of different components that are under service conditions and can cause serious accidents & property loss or even can cause death sometimes.

Common Precautions for Welding Defects

Having already said that, defects are parts of welding but you can take necessary precautions to reduce the chances of defects. Few common precautions before starting welding include

Common Precautions to Welding Defects

  • Welding material should be clean & in good shape
  • Make sure before welding that the welding metal doesn’t contain any contaminations
  • Remove any paint or oil from the weld metal
  • Make sure the welding pieces fit together correctly
  • Current is used according to the need

Classification of Defects According to their Appearance

Welding defects have been classified into 6 groups according to IIW

  • Cracks
    All types of crack defects are included in this category like crater crack, hot cracks, and cold cracks.
  • Cavity
    All types of cavity defects are included in this category like porosities, blowholes, shrinkage & pipes.
  • Incomplete Fusion & Penetration
    This includes all types of lack of fusion & lack of penetration.
  • Solid Inclusion
    Solid inclusion includes slags, metal oxides, tungsten & wagon track, etc.
  • Imperfect Shape
    Imperfect shapes include undercut, underfill, overlap, excessive penetration & improper bed shape, etc.
  • Miscellaneous Defects
    This category includes arc strike, excessive spatter, rough spatter, uneven ripples, etc.

Categories of Welding Defects

Welding defects have been classified into two categories.

  1. Visual/External Defects

  2. Hidden/Internal Defects

Visual/External Defects

External defects consist of following common types of defects.

  • Crack
  • Porosity
  • Undercut
  • Overlap
  • Spatter
  • Arc Blow
  • Excessive Penetration

Now let’s look at each visual defect thoroughly with examples & real-life images where necessary.


The most common type of welding defects is a crack. Cracks may be of micro or macro size. They can appear almost everywhere in the weld like, on the surface, inside the weld or at heat-affected zones.

How Cracks Occur?

Weld Cracks occur due to the intense heat of welding i.e. when localized stress exceeds the limit of tensile strength. During solidification of weld metal process shrinkage occurs and these stresses are developed.


Crack Symbol-Welding Defect

Practical Example

Cracks-Welding Defect

Causes & Remedies of Weld Cracks
Causes of Weld Cracks

Weld cracks may appear due to the following reasons

    • High Sulfur and carbon contents
    • Sensitive chemical composition to cracking
    • Irregular size & shape of weld bead produced by welding parameters results into cracks
    • Poor ductility of base metal
    • High arc travel speed
    • High hydrogen contents in the weld metal while welding ferrous material
    • Fast cooling rates

Remedies of Weld Cracks

Weld cracks can  be reduced by taking following precautions

  • Avoid contamination of weld pool
  • Avoid contamination of parent metal with grease & oil
  • Properly preparing joint before welding
  • Controlled welding parameters are one of the important remedies
  • Moderate cooling
  • Average arc travel speed to produce wider bead
  • Use low welding current setting to produce shallower bead

Categories of Cracks
  • Longitudinal cracks
  • Transverse cracks
  • Radiating cracks
  • Welder crater cracks
Types of cracks
  1. Hot cracks
  2. Cold cracks
  3. Crater cracks
Hot Cracks

Shrinkage cracks formation during the solidification of weld metal is known as hot cracking.  It is also known as hot shortness, solidification cracking, liquation cracking & hot fissuring. When the available liquid weld metal is inadequate to fill the spaces between solidifying metal then these are cracks are certain to appear.

Cold Crack

Cold crack is generally known as spontaneous crack &  occurs when the solidification process is completed & temperature is below 200oC. Cold cracking is sometimes also known as “Delayed Cracking” because it can develop hours or days after the welding has been completed. Cold cracking occurs mostly in carbon steels, low alloy steel & high alloy steels &  it can be prevented only when preheating is employed.

Crater Crack

If the arc is broken before the crater is filled, it will cause the outer edges to cool faster than the crater & will cause crater cracks. Crack is formed as a result of produced stresses. When the weld pools start cooling down and solidification occurs, it must contain adequate volume to overcome weld metal shrinkage, if not then crater cracks will be formed. Crater cracks occur at the ending point of a weld. Worst disadvantage of crater cracks is that they can cause more cracks


The kinds of welding defects that occur when gas or small bubbles are trapped in the welding zone is called as porosity. Porosity is actually tiny holes in the weld.

Porosity can cause a serious problem in STICK or MIG welding. When molten puddle cools down it releases gases of hydrogen and carbon dioxide, if these gases don’t reach the surface before solidification then they get trapped in the weld & cause weakness of joints.


Practical Example

Cracks-Welding Defect

Causes & Remedies of Porosity
Causes of Porosity

  • Contaminated surface
  • Presence of rust, oil, grease & paint
  • Improper gas shield
  • Inadequate electrode de-oxidant
  • Using longer arc
  • Presence of Moisture
  • Wrong surface treatment
  • Too high gas flow use
  • High welding currents

Remedies of Porosity

  • Proper electrode selection having a low hydrogen content
  • Lowering welding current
  • Using smaller arcs
  • Slowly welding to allow the gases to escape
  • Proper cleaning of the surface
  • Using dry material
  •  Using a proper welding technique


This welding defect occurs when the base of the metal melts away from the weld zone, consequently forming a groove in the form of a notch at the toe of the weld.

Undercut reduces the CROSS-SECTIONAL thickness of the base metal, which results in the weakness of the workpiece and weld.

When more than one passes are welded on the joint, chances of undercutting increase. If you do a pass & notice undercutting, you should remove the undercut before making the next pass. Otherwise, there is a risk of trapping slag onto the welded joint. Undercutting can ruin the QUALITY of the weld. Also, undercutting can be easily spotted after weld.

SymbolUndercut Symbol-Welding Defect
Practical Example

Causes & Remedies of Undercut
Causes of Undercut

  • High weld current
  • Fast welding speed
  • Wrong welding angle
  • Too much large arc
  • poor welding technique
  • Too much larger electrode
  • Wrong filler metal
  • Wrong use of shielding gas

Remedies of Undercut

  • Reducing arc length or low arc voltage
  • Moderate electrode travel speed
  • Using correct shielding gas combination
  • Using proper electrode angle i.e. from 30 degree to 45 degree with standing legs
  • Using proper and limited current
  • Choosing a correct welding technique
  • Using the multi-pass technique
  • Using an electrode of smaller diameter


This welding defect occurs when weld face extends more than the toe of the weld, this causes the weld metal to roll and & form an angle less than 90O.


Overlap Symbol-Welding Defect

Practical Example

Overlap-Welding Defect

Causes & Remedies of overlap
Causes of Overlap

  • Wrong use of welding technique
  • Using an electrode of large size
  • High welding current

Remedies of Overlap

  • Using proper welding technique
  • Using small electrode size
  • Less welding current


This welding defect occurs when small particles of the metal attach themselves to the surrounding surface of the material. This is most common in gas metal arc welding (GMAW). It can’t be completed eliminated from the welding instead it can only be minimized while grinding.


Spatter Symbol-Welding Defect

Practical Example

Spatter-Welding Defect

Causes & Remedies of Spatter
Causes of Spatter

  • High welding current
  • Low voltage settings
  • Steeper angle of working electrode
  • Contaminated surface
  • Inconsistent wire feeding
  • Long arc
  • inadequate gas shielding
  • Incorrect polarity

Remedies of Spatter

  • Low welding current
  • Reducing arc length
  • Surface cleaning before welding
  • Using correct shielding gas
  • Removing feeding issues
  • Increasing electrode angle
  • Correct use of the polarity according to the condition

Arc Blow

Arc blow is actually the deflection of electric arc from its intended path i.e. the axis of the electrode. Arc blow is similar to the wavering of flame due to the wind’s, the only difference is arc blow happens due to magnetization instead of wind.
Arc blow is mainly caused when DC arc welding is used. It happens due to the interaction between different electromagnetic fields around the welding arc.


Practical Example

Arc Blow-Welding Defect

Common Situations that can Cause Arc Blow

There are commonly two situations of interaction between electromagnetic fields

  • Interaction due to current flow through the arc gap & that due to current flow through plated being welded.
  • Interaction due to current flow through the arc gap & that is localized while welding near the edge of the plates.
Kinds of Arc Blow
Magnetic Arc Blow

Magnetic arc blow is actually deflection of welding filler material within an electric arc deposit by a buildup of magnetic force surrounding the weld pool.

Causes of Magnetic Arc Blow

  • Workpiece connection
  • Poor fit-up
  • improper Equipment settings
  • Joint Design
  • Atmospheric conditions (Windy conditions play a big role)
Thermal Arc Blow

Thermal Arc blow is mostly connected to the variations in resistance within the base metal created by the weld pool when it is moved across the workpiece.

Causes of Thermal Arc Blow

  • Irregular travel speed
  • Long arc length
  • Irregular surface preparation
  • When compared with each other Magnetic Arc blow is more dangerous than Thermal Arc Blow

Major Causes of Arc Blow
Causes of Arc Blow

  • Any material that has a Magnetic field tends to produce arc blow which is a common phenomenon in steels. If magnetic field strength is greater than ~50 Gauss then arc blow is most common to happen.
  • When DC (Direct Current) is used & welding material has a certain level of Magnetism arc blow is expected to appear.
Remedies of Arc Blow
Remedies of Arc Blow

  • Make sure to use AC (Alternating Current) rather than DC (Direct current) to avoid Arc blow welding defect
  • Try to keep the Arc as short as possible i.e. lower arc voltage
  • Use the lowest practical current value
  • Use multiple earth connections to remove the backward arc blow & forward arc blow
  • Residual magnetism can be reduced in the steel within a tolerable level to reduce the chances of Arc blow
  • While welding, try to weld away from the earth clamped connection. Make sure to split the earth clamp & correct to both sides of the joint

Excessive Penetration (Excess Penetration Bead)

The type of defect which occurs when weld metal is lying outside the plane joining the toes is called as excessive penetration. Excessive penetration produces notches which are responsible for stress concentration. It is also completely an economic waste.


Practical example

Excessive Penetration-Welding Defect

Causes & Remedies of Excessive Penetration 
Causes of Excessive Penetration

  • When the root gap is too high
  • When high welding current is used
  • When slow arc speed is used
  • When larger size electrodes are used

Remedies of Excessive Penetration

  • Use proper current Value
  • Fitting-up joint accordingly
  • Use correct root Face
  • Use Proper welding technique

Hidden/Internal Defects

Internal defects consist of following common types of defects.

  • Slag Inclusion
  • Incomplete/Lack of Fusion
  • Necklace Cracking
  • Incomplete/Lack of Penetration

Now let’s look at each hidden defect thoroughly with examples & real-life images where necessary.

Slag Inclusion

Slag inclusion is one of those welding defects which is easily visible in the weld. Slag ruins structural performance & quality of the weld. Slag is actually the waste material which is produced during welding process. Bits of slag that contains flux, rust & tungsten material are trapped into the weld area and become source of contaminations. Slag is actually a byproduct of shielded metal arc welding, flux cored arc welding, submerged arc welding & even gas metal arc welding.


Slag Inclusion Symbol-Welding Defect

Practical Example

Slag Inclusion-Welding Defect

Causes & Remedies of Slag Inclusion
Causes of Slag Inclusion

  • Improper cleaning
  • High weld speed
  • No cleaning during the welding passes
  • Wrong welding angle
  • High cooling speed of the weld pool
  • Too low current used
  • Improper welding rod rate

Remedies of Slag Inclusion

  • Proper surface cleaning
  • Moderate welding speed
  • Clean surface after each welding pass
  • Correct welding & electrode angle
  • Proper welding rod rate
  • High currents
  • Reduce rapid cooling

Incomplete/Lack of Fusion

The type of welding defect which occurs when weld beads don’t fuse together properly or there is a lack of proper fusion between the base and weld metal. As a result a gap is created & is not filled with the molten metal.
Most common type of the incomplete fusion is known as overlap & occurs at the toe of the weld.


Lack of Fusion Symbol-Welding Defect

Practical Example

Causes & Remedies of Incomplete Fusion
Causes of Incomplete Fusion

  • Incorrect weld angle
  • Small thickness of the electrode
  • Wrong selection of the electrode
  • Fast travel speed
  • Short arc length
  • Too low current & low value of heat input
  • large weld pool
  • Impurities of the base metal surface

Remedies of Incomplete Fusion

  • Use high current with proper arc voltage
  • Proper cleaning of the surface before welding
  • avoid molten pool from submerging the arc
  • Reduce deposition rate
  • Using electrode of correct diameter and correct angle
  • Proper positioning of the bead

Necklace Cracking

Necklace cracking occurs when EBW (Electron Beam Welding) is used. Most of the time this defect occurs when the weld doesn’t penetrate properly. In the presence of improper penetration molten metal doesn’t flow into the cavity & a cracking defect is formed which is known as Necklace Cracking.

Practical Example

Necklce Cracking-Welding Defect

Causes & Remedies of Necklace Cracking

Causes of Necklace Cracking

  • Improper welding technique
  • High speed Electron Beam Welding (EBW)
  • Mostly Necklace cracking occurs in alloys

Remedies of Necklace Cracking

  • Using a proper welding technique
  • Using a constant feed speed
  • Use proper material for welding

Incomplete/Lack of Penetration

Incomplete penetration occurs when filler and base metals are not joined properly or metal groove is not filled completely. This welding defect mostly occurs in butt welds. A gap or some sort of a crack is formed as a result of incomplete penetration. Welds which contain incomplete penetration are weaker and are almost useless.


Incomplete Penetration Symbol-Welding Defect

Practical Example

Incomplete Penetration-Welding Defect

Causes & Remedies of Incomplete Penetration
Causes of Incomplete Penetration

  • More space between the welding metals
  • High bead moving speed
  • Using too low current
  • Using Improper joint
  • Using electrode of large diameter
  • Improper welding technique
  • Inadequate deposition of the weld metal
  • Too Narrow groove angles

Remedies of Incomplete Penetration

  • Using proper joint geometry
  • Reduce arc travel speed
  • Choosing suitable current amount
  • Proper alignment of the metals
  • Moderate bead moving speed
  • using electrode of proper size
  • More deposition of the weld metal
  • Proper groove angles


Since welding defects can put a huge impact on the failure of any components that is why early inspection & modification is inevitable to avoid any kind of failure which may lead to greater loss of either property or human deaths. 

Highly advance & sensitive techniques are necessary for the detection of any discontinuities or defects so that danger of risk can be removed earlier by repairing/maintenance where necessary. 

Some suggested Readings :

11 Most Familiar Types of Welding Defects|Causes| Remedies|Practical Examples|Symbols
Article Name
11 Most Familiar Types of Welding Defects|Causes| Remedies|Practical Examples|Symbols
When the Irregularities formed in the weld metal exceed some code limitations then they are called as Welding defect
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The Welding World
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