What is the difference between a weld defect and discontinuity?

A Discontinuity is an objective lack of material, an interruption in the physical consistence of a part while a Defect is an excessive conditions, outside the acceptance limits, which risks to compromise the stability or the functionality of the welded structure. It is very hard to perfect welding.

What is a weld discontinuity?

Weld discontinuities can be defined as "an interruption of the typical structure of a weld, such as a lack of homogeneity in the mechanical, metallurgical or physical characteristics of the weld." Weld discontinuities include porosity, slag inclusions, incomplete fusion, incomplete joint penetration, excessive melt- ...

What determines whether a weld discontinuity is a defect?

All welding defects are developed discontinuities. If a discontinuity renders a weld incompetent or lowers its quality, it would be classified as a defect. Defects make the product risky to use or substandard. It is up to the quality control to decide whether the discontinuity qualifies as a defect or not.

What is a defect in a weld?

Welding defects can be defined as weld surface irregularities, discontinuities, imperfections, or inconsistencies that occur in welded parts.

What is a discontinuity in NDT?

Discontinuity: a lack of continuity or cohesion; an intentional or unintentional interruption in the physical structure or configuration of a material or component. Flaw: an imperfection or discontinuity that may be detectable by nondestructive testing and is not necessarily rejectable.

What is the difference between discontinuity and defect

What do you mean by discontinuities?

Definition of discontinuity

1 : lack of continuity or cohesion. 2 : gap sense 5. 3a : the property of being not mathematically continuous a point of discontinuity. b : an instance of being not mathematically continuous especially : a value of an independent variable at which a function is not continuous.

What is the difference between an indication and discontinuity?

The four major terms are highlighted in colour and you'll notice only "Indication" is on the right side under the banner of "On Screen". Discontinuities, flaws and defects are actual physical things in the part (left side), and indications are on your screen (right side).

What are the two types of welding defects?

Welding defects are broadly classified into two categories, and those are: External welding defects (Defects occur on the upper surface of the welded work). Internal welding defects (Defects occur under the surface of the welded work).

What are 5 welding defects?

Following are the types of welding defects:

• Porosity and Blowholes.
• Undercut.
• Weld crack.
• Incomplete fusion.
• Slag inclusion.
• Incomplete penetration.
• Spatter.
• Distortion.

What are the 7 common welding defects?

How to Identify the 7 Most Dangerous Welding Defects

• Types of Welding Defects.
• Slag Inclusions.
• Porosity.
• Undercut.
• Weld Crack.
• Incomplete Fusion.
• Incomplete Penetration.
• Spatter.

Do all welds have discontinuities?

The truth is that all welds have flaws, or discontinuities, but some have so many that they fail quality assurance tests and are ultimately considered. Welding discontinuities should be taken seriously because they can render all of the time, effort and energy you put into a weld completely pointless.

How can you prevent welding discontinuities?

You'll need to remove the impurities in your metal and preheat it as required. Additionally, use the proper joint design for the material and properly cool the welded area. Be sure to weld enough sectional areas, too. Use the right amperage current and welding speed.

What is discontinuity material?

A discontinuity is an imperfection or interruption in the normal physical characteristics or structure of a material (e.g. crack, porosity, and inhomogeneity etc.).

Is weld spatter a defect?

Welding spatter is a welding defect. During welding operation due to the force of arc, some of the molten metal particles are jumping from weld pool and falling into other areas of the plate is called as spatter.

What are the causes of welding defects?

• Wrong joint design.
• Contamination of the base metal coupled by poor ductility.
• Use of hydrogen gas as a shield gas while welding ferrous metals.
• High content of carbon and sulfur in the base metal.
• High welding current.
• Rapid cooling of the weld joint.
• Inadequate preheating.
• Residual stress can also lead to cracks.

Is porosity a discontinuity?

Porosity is defined as cavity-type discontinuities formed by gas entrapment during solidification. Porosity is caused by gases that are present in the molten weld.

What determines if a discontinuity is acceptable?

Evaluation of the discontinuity will determine if the discontinuity is a defect or an acceptable condition: Incomplete Fusion - A weld discontinuity in which fusion did not occur between weld metal and fusion faces or adjoining weld beads.

Why is it important to identify welding defects?

Welding control is an extremely important action: defects, visual or otherwise, can compromise the final job and lead to breakage.

How do you determine welding defects and strengths?

Small defects such as these can be verified by Liquid Penetrant Testing (Dye check). Slag inclusions and cracks just below the surface can be discovered by Magnetic Particle Inspection. Deeper defects can be detected using the Radiographic (X-rays) and/or Ultrasound (sound waves) testing techniques.

What is the difference between undercut and underfill?

So how do we differentiate undercut from underfill? In a nutshell, undercut occurs in base metal adjacent to the weld, and underfill occurs in the weld metal. Although undercut can occur on both grooves and fillets, underfill will occur only on grooves. Fillets would be considered undersize.

What causes whiskers in a weld?

Whiskers are short lengths of electrode wire sticking through the weld on the root side of the joint. They are caused by pushing the electrode wire past the leading edge of the weld pool. Whiskers can be prevented by: (1) Reducing the wire-feed speed and the speed of travel.

Which defect in welding is called external defect?

External welding defects are found on the surface itself and can sometimes be recognized by naked eyes. Surface Cracks, Undercut, Porosity, Overlaps, Crater, Underfill, Spatters, Excessive penetration, Arc Strike, etc are examples of external welding defects.

What is indication in welding?

Linear indications are mainly cracks, lack of penetration, lack of fusion, and elongated slag inclusions. Rounded Indication: Any indication with a length equal to or less than three times the width. A rounded indication may be circular, elliptical, conical, or irregular in shape and may have tails too.

What is a false indication?

False Indication - A test indication that could be interpreted as originating from a discontinuity but which actually originates where no discontinuity exists.