What is the difference between defects & discontinuities?

Discontinuity

An interruption of the typical structure of a material,

Such as•a lack of homogeneity in its mechanical, metallurgical, or physical characteristics.

A discontinuity is not necessarily a defect.

Defect

A flaw or flaws by nature or accumulated effect renders a part or product unable to meet minimum applicable acceptance standards or specifications.

The term designates rejectability.

Defects :

Welding Defects are excessive conditions, outside the acceptance limits of deviations, which risks to compromise the stability or the functionality of the welded structure.

Discontinuity :

An interruption of the typical structure of a material, such as a lack of homogeneity in its mechanical, metallurgical, or physical characteristics. A discontinuity is not necessarily a defect.

Many thanks for invitation, 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

DEFECT WHICH IS NOT ACCEPTABLE.

DISCOUNTINUITIES CAN BE ACCEPTED 

A defect may affect the serviceability of a part or material.

A discontinuity may or may not affect the serviceability of a part or material.

A good understanding of these two terms is a basic but very important piece of knowledge every NDT practitioner must be fully aware of.

All Defects are Discontinuity but all Discontinuity are not defect because some discontinuity are acceptable

A discontinuity will survive a field test while a defect won’t

Discontinuities are the flaws or irregularities in welds or weldments subject for evaluation if suitable for intended purpose. While the defect is the specific discontinuity deemed unsuitable for its intended purpose base on criteria on applicable codes 

• Any weld would be a defect if the welder or the quality control department rejects it and blacklists the product
• A defined list of acceptable discontinuities will list the number or type of discontinuities allowed on a product before labelling it a defect
• A discontinuity will survive a field test while a defect won’t. A crack on a water pope would be a defect since the water will leak while an unacceptable profile could pass as a discontinuity as long as the pipe doesn’t leak

A defect is a flaw which compromises the integrity or usefulness of the  weld, while weld discontinuities are interruption of the typical structure of the material such as lack of homogeneity in its mechanical, metallurgical, or physical characteristics. A discontinuity could be the result of a defect, but isn't necessarily a defect

Weld discontinuities, includes:

1. Porosity.
2. Incomplete fusion.
3. Incomplete joint penetration.
4. Unacceptable weld profiles.
5. Cracking.

Defects unacceptable imperfection, discontinuity is may be acceptable.