Overview of Weld Defects 222

Overview of Weld Defects provides a comprehensive introduction to the most common varieties of weld discontinuities and distortion. It illustrates the causes of each of the twenty different weld discontinuities and defects and suggests effective solutions. In addition, it presents an overview of six different kinds of cracks and demonstrates how to prevent cracking and distortion in a finished weld.

This class is especially crucial for beginning welders who do not yet have the skills or knowledge to avoid many of the mistakes that the class illustrates. Beginning welders will find this class particularly useful because it defines the reasons why defects or discontinuities may occur as well as the ways in which welders may rectify them.

  • Difficulty Intermediate

  • Format Online

  • Number of Lessons 19

  • Language English


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Course Outline
  • Introduction to Weld Defects and Discontinuities
  • Misalignment, Undercut, and Overlap
  • Excessive Spatter and Arc Strikes
  • Slag Inclusion, Tungsten Inclusion, and Porosity
  • Defects and Discontinuities Review
  • Incomplete Fusion and Penetration, Excessive Reinforcement, and Improper Leg Size
  • Non-Uniformity, Gas Marks, Craters, and Burnthrough
  • Defects and Discontinuities Review
  • Weld Distortion
  • Minimizing Distortion and Shrinkage
  • Backstep Welding
  • Longitudinal and Transverse Cracking
  • Less Common Cracks
  • Distortion and Shrinkage Review
  • Visual Inspection
  • Destructive Testing
  • Nondestructive Testing
  • Discontinuities and Defects in Practice
  • Weld Inspection and Testing Review
  • Distinguish between defects and discontinuities.
  • Describe misalignment, undercut, and overlap.
  • Describe excessive spatter and arc strikes.
  • Describe slag inclusion, tungsten inclusion, and porosity.
  • Describe incomplete fusion, incomplete joint penetration, excessive reinforcement, and improper leg size.
  • Describe non-uniformity, gas marks, craters, and burnthrough.
  • Describe weld distortion.
  • Explain how to minimize distortion and shrinkage.
  • Describe backstep welding.
  • Contrast longitudinal and transverse cracking.
  • Identify less common types of weld cracks.
  • Describe visual weld inspection.
  • Describe destructive weld testing.
  • Describe nondestructive weld testing.
  • Explain the importance of detecting discontinuities and defects.
Vocabulary Term

American Welding Society

AWS. A professional organization that supports the welding industry and promotes welding and related processes. The AWS provides industry-standard code and certification procedures.


A measurement of the amount of current flowing in a circuit. Amperage is measured in amperes.

arc length

The distance the arc stretches from the electrode to the workpiece. Longer arcs require more voltage.

arc strikes

A welding discontinuity which appears as a small, raised circle or line on the workpiece. Arc strikes are caused when the arc is begun outside the weld area.


The removal of weld metal and base metal from the side opposite to a partially welded joint. Back-gouging can be used to correct incomplete penetration.

backstep welding technique

A welding technique in which small welds are made in the opposite direction from the general direction of the weld. The backstep welding technique is continued until the full weld is completed.

base metal

One of the two or more metals to be welded together to form a joint. Base metals should be clean in order to ensure a strong weld.

bend test

A destructive test in which a small sample of a weld is bent into a U-shape. Bend tests allow inspectors to observe strength, flexibility, and some discontinuities.


A discontinuity in which weld metal from one side of a joint melts through to the other. Burnthrough can leave an open hole in the joint, which must then be ground down and re-welded.


A handheld instrument that includes one or more set of jaws to measure various part dimensions. Calipers include indicators on the top of the instrument that expand to measure internal diameters.

centerline cracks

A gap or break in the surface of a weld that is parallel to the weld axis and is along the centerline of the weld. A centerline crack is a type of longitudinal crack.

Certified Welding Inspector

CWI. A person certified by the American Welding society to inspect welds and interpret AWS and other codes. CWIs are often crucial in ensuring weld quality.

Charpy test

An impact test that measures the amount of energy a material can absorb. Charpy tests break the material using a falling pendulum then measure the pendulum's upswing.

chipping hammer

The hammer used to scrape slag from a cooled weld bead. The chipping hammer is sometimes called a scaling, or slag, hammer.


Holding a tool or workpiece in place. By clamping a workpiece in place and properly measuring it, welders can avoid misalignment.


Securing a workpiece or workpieces in place using a device that applies inward pressure. Clamping can help to minimize distortion in a weld.


Curving inward. Concave weld surfaces can result in longitudinal cracking.

confined spaces

An area with limited means of entry or exit that is large enough for a worker to enter but is not designed for continuous occupancy. Confined spaces make X-ray testing difficult.


Any substance not original to a weld that may interfere with the efficacy of the weld. Contaminants with low melting points may result in longitudinal weld cracking.


Curving outward. Convex crater surfaces do not usually distort when cooling.

corner joint

A weld that joins two metal parts at right angles to one another. Corner joints require large amounts of weld metal.

crater cracks

A small crack in the center of a crater in a weld. Crater cracks can be avoided by using the proper weld ending techniques to ensure the crater is flush with the weld surface.


Any type of information gathered about a product or process. Data is often in the form of values or numbers.


A weld discontinuity which is so severe that it compromises the integrity of the weld. Defects must be repaired, or the welded part must be discarded.

destructive testing

A testing method that places materials in harsh conditions that lead to product failure. Destructive testing includes the guided band test and transverse tension test.


A liquid or other substance which is designed to draw penetrant from weld defects so that they can be easily seen. Developers are used in liquid penetrant inspection.


An interruption or flaw in the typical structure of a weld. Discontinuities may also be defects.


Able to be drawn, stretched, or formed without breaking. Ductile materials generally have low strength.


A device in an electrical circuit that conducts electricity. Electrodes also act as filler metal in some arc welding processes.


A magnet which is electrically charged by a current-carrying coil wound around it. Electromagnets can produce larger magnetic fields than magnets that are not electrically charged.

electromagnetic testing

A nondestructive testing method in which electric current or magnetic fields are used to determine if a weld is defective. Electromagnetic testing creates an observable change in the magnetic field when an internal defect is present in a weld.

excessive reinforcement

The use of more weld metal than is required to fill a weld joint. Excessive reinforcement is sometimes called overfill.

excessive spatter

A welding discontinuity in which small pieces of molten metal have scattered on the workpiece. Excessive spatter does not affect weld strength and can usually be ground or chipped away.


The exposed surface of a weld. The face may be convex, concave, or, in the case of a groove weld, flush with the workpiece.


When a weld breaks, stretches, or separates, making it unstable. A weld fail results in the weld being unusable.

ferromagnetic material

A type of material that is highly attracted to magnets and can become permanently magnetized. Ferromagnetic materials include iron and nickel.

filler metal

Metal deposited into the weld that often adds strength and mass to the welded joint. In some arc welding processes, the electrode acts as the filler metal.

fillet weld

A type of weld that is triangular in shape and joins two surfaces at right angles to each other. Fillet welds are the most common types of welds.

fillet weld break test

A destructive test in which a fillet weld is subjected to pressure from the opposite side. Fillet weld break tests expose a surface that reveals discontinuities within the weld.


A device used to measure a finished weld. Gages are available in many different varieties, each designed to measure a different aspect or number of aspects of different kinds of finished welds.

gas marks

A discontinuity in which gas bubbles from the arc become trapped in the weld puddle. Gas marks form when slag solidifies and a trapped gas bubble marks the weld bead.

gas metal arc welding

GMAW. An arc welding process in which a consumable bare wire electrode and shielding gas are fed into the weld. GMAW is also known as MIG welding.

gas tungsten arc welding

GTAW. A very precise arc welding process that uses a nonconsumable tungsten electrode. GTAW is also referred to as TIG welding.


A steel or iron beam used as part of the support structure for a large building. Welds on a girder are subject to rigorous inspection.


The use of an abrasive to wear away the surface of a workpiece and change its shape. Grinding is an important part of weld defect repair.

groove welds

A type of weld made in the opening between the surface of two parts that provides space to contain weld metal. Groove welds are used on all joints except lap joints.

heat-affected zone cracks

HAZ cracks. Cracks that form in the heat-affected zone of the base metal. HAZ cracks can be both longitudinal and transverse.


A colorless, odorless gas that is the most abundant element in the world. Excess hydrogen may result in transverse weld cracking.

impact strength

The ability of a metal to withstand high energy without fracturing or breaking. The impact strength of a weld can be determined by putting the weld through different types of impact testing.

impact testing

A destructive test that involves a hammer or other object impacting the weld. Impact testing includes Charpy tests.

improper leg size

A fillet weld discontinuity in which the weld legs are not equal in length. Improper leg size is not a defect as long as the shorter leg meets the size requirement of the weld size.

incomplete fusion

A weld discontinuity in which the weld metal and base metal or adjoining weld beads are not fully fused. Incomplete fusion significantly weakens the integrity of a weld.

incomplete penetration

A weld defect in which an area of a joint is unpenetrated and unfused. Incomplete penetration occurs when weld metal does not extend through the thickness of the joint.


The examination of a part during or after its creation. Inspection confirms that parts adhere to specifications.

insufficient reinforcement

The failure of a welder to properly fill a joint with metal. Insufficient reinforcement can be corrected by making another pass over the joint to level the surface of the weld with the surface of the base metal.


The meeting point of two materials that are fused together. Welding creates a permanent joint.

joint penetration

The depth to which arc heat can melt a joint below the surface of its base metals. Joint penetration is directly affected by the amount of amperage.

liquid penetrant inspection

A nondestructive testing method which can reveal surface discontinuities on a weld. Liquid penetrant inspection requires an inspector to apply a penetrant and then a developer to reveal weld discontinuities.

longitudinal crack

A gap or break in the surface of a weld that is parallel to the weld axis and may be along the centerline of the weld or near the weld toes. Longitudinal cracks include centerline and heat-affected zone cracks.

macro-etch testing

Destructive testing that involves polishing and etching small cross-sections of a welded joint using a mild acid mixture. Macro-etch tests enable examination of the internal structure of a weld.

magnetic particle inspection

MPI. A nondestructive testing method in which iron oxide particles accumulate in the cracks or seams of a magnetized part. Magnetic particle inspection can reveal discontinuities on highly magnetic materials.

magnifying glass

A small, handheld lens designed to magnify the user's view of an object. Magnifying glasses can be used in visual weld inspection.


A U-shaped measuring instrument with a threaded spindle that slowly advances toward a small anvil. Micrometers are available in numerous types for measuring assorted dimensions and features.


A weld discontinuity in which two or more workpieces are not properly aligned before they are welded. Misalignment is often called high-low.


A small slot, of specific dimensions, cut into a metal sample of specific dimensions. Nicks are used to locate the exact fracture point upon impact in a nick break test.

nick break testing

A destructive test in which a small slot is cut into the surface of the weld and the weld is then broken across that slot. Nick break testing allows inspectors to not only measure the strength of a weld but also to examine it for internal defects.


A discontinuity in which the thickness of a weld bead is uneven along its length. Non-uniformity is unsightly but not necessarily a defect.


The use of more weld metal than is required to fill a weld joint. Overfill is sometimes called excessive reinforcement.


A weld discontinuity in which the weld metal protrudes beyond the weld toe or weld root. Overlap is nearly always unacceptable in a finished weld.


Two lines that are equidistant from one another and do not intersect. A longitudinal crack is parallel to the direction of a weld.


Striking a weld with a hammer to flatten it and stretch it out. Peening can be used to reduce distortion in the workpiece.


A powder or dry aerosol applied material that is designed to penetrate weld defects. Penetrants are used for liquid penetrant inspection.


An intersection of two lines or objects at right angles. A transverse crack runs perpendicular to the direction of a weld.


A discontinuity characterized by the appearance of tiny voids or bubbles on or in a weld bead. Porosity results from gases being trapped in a material and can weaken a weld.


The application of heat to a base metal after welding. Post-heating helps to remove hydrogen and ensure a solid weld.


The application of heat to a base metal immediately before welding. Pre-heating helps reduce hardness in the metal.


A machine with a stationary base and an upper arm that moves along a vertical axis. Presses are often used in the fillet weld break test.


The point at which the back of a weld intersects the surfaces of the base metal. Weld roots may experience defects due to misalignment.

sanding disc

A round piece of woven or nonwoven material covered in a coated abrasive. Sanding discs are rotated by motorized devices to remove material from a part surface.


A gas or type of flux that provides protection to the weld area. Insufficient shielding can cause porosity in a weld.


A reduction in size that is created as a weld cools. Shrinkage can lead to distortion.


Cooled flux that forms on top of a weld bead. Slag protects cooling metal and is then chipped off.

slag inclusion

A discontinuity in which small particles of cooled flux become lodged in the weld metal. Slag inclusion can significantly decrease the strength of a finished weld.


A large hammer, usually with a head from 10 to 20 pounds (4.5 to 9 kilograms). Sledgehammers can be used for informal, less-precise impact testing.


A weld or metal workpiece's ability to resist outside forces that are trying to break or deform the weld or metal. High levels of strength are generally preferable in a welded joint.


A force that attempts to deform an object. Excess stress may result in transverse weld cracking.


The shortest distance between the weld root and a line drawn between the weld toes. The throat determines a weld's size and strength.

throat crack

A crack in the throat of a weld. Throat cracks are often caused by shrinkage or filler metal with inadequate strength.


The point at which a weld face and base metal meet. Weld toes can experience undercut and cracking.

toe crack

A crack in the toe of a weld. Toe cracks are caused by shrinkage.


An acceptable deviation from a desired dimension that still meets specifications. Tolerances indicate the allowable difference between a physical feature and its intended design.

transverse crack

A gap or break in the surface of a weld that is perpendicular to the weld axis. Transverse cracks may be completely within the weld metal or may extend from the weld metal into the base metal.

transverse tension test

A destructive test that pulls a weld until it breaks. Transverse tension tests are generally required as part of mechanical testing for groove welds.

travel speed

The speed at which the welder moves the electrode along the joint to make a weld. Travel speed determines the size of the weld bead.


A gray metal that is very strong at elevated temperatures. Tungsten may become trapped in a weld, causing a defect.

tungsten inclusion

A weld defect caused by tungsten particles entrapped in the weld metal. Tungsten inclusion only occurs in gas tungsten arc welding.

ultrasonic inspection

A nondestructive testing method that sends high-frequency sound waves through a material to locate discontinuities. Ultrasonic inspection records data that the inspector can then interpret.


A weld discontinuity in which a groove melted into the base material, usually along the toe of the weld, which produces a weak spot in the weld. Undercut can be caused by excessive current, poor welding technique, or incorrect filler metal.


The failure of a welder to properly fill a joint with metal. Underfill can be corrected by making another pass over the joint to level the surface of the weld with the surface of the base metal.

visual inspection

A visual assessment of surface defects. Visual inspection is one of the most commonly used non-destructive inspection methods for finished welds.


E. The electrical force or pressure that causes current to flow in a circuit. Voltage is also called electromotive force.

weld cracking

A fracture or separation that develops in a weld once the weld solidifies. Weld cracking can be caused by clamping the workpiece.

weld distortion

Warping in the base metal due to stresses caused by heating. Weld distortion is caused by base metal expansion due to the heat of the welding process and the subsequent contraction as the metal cools.

weld passes

One progression of welding across a joint. Each weld pass creates a weld bead.


The person who performs a weld. Some reference materials may also refer to the power source used for arc welding as a welder.

welding codes

A standard used to govern welding processes. Welding codes ensure safe welding practices and high-quality welded products.

welding procedure specifications

WPS. A written document that contains all of the necessary and specific information regarding the application of a welding project. WPS must be approved and tested before they can be used.

width-to-depth ratio

A measure of the width of a weld in comparison to its depth. An improper width-to-depth ratio can cause cracking.

X-ray testing

A non-destructive testing method in which the use of an x-ray machine to examine the interior of a completed weld. X-ray testing is expensive and time-consuming and therefore is typically only used in situations where the weld must be perfect.


An electromagnetic wave. X-rays are used in inspection to examine the mechanical bond strength of each joint or weld.