Welding imperfections and welding defects

Imperfections and defects

The terms of “defects” and "imperfections?

BS EN ISO 6520-1 definitions

Imperfections: any deviation from the ideal weld.
Defect: an unacceptable imperfection

ASME B31.3 definitions

Defects : the imperfections of a type or magnitude not acceptable by the criteria specified in para. 341.3.2 and shall be repaired, or the defective item or work shall be replaced.

Classification of welding imperfections (ASME BPVC. V)

Burn through

A collapse of the weld pool, mainly causes of an excessive welding current.

It is normally found at the center of the root pass and in RT film with variable density (darken areas).

I hope you can find out more causes of imperfection and preventive actions in CSWIP Training Source.

This imperfection is commonly found in the semi-auto / auto welding process.

A SAW process easy found at start arc, stop arc or variation arc length. That are the reasons we should make the run-in plate and run-out plate during welding.

Cracks

Crack is an imperfection produced by a local rupture in the solid state, which may arise from the effect of cooling or stresses.

ASME B31.3 grounded in the “extent of imperfection”; unacceptable regardless any size and location.

AWS D1.1 Crack prohibition, any crack shall be unacceptable, regardless of size or location.

Radiographic image: a line of darker density running lengthwise along the weld at any location in the width of the weld image

Excessive / inadequate reinforcement

Excess weld metal is the extra metal that produces excessive convexity in fillet welds and a weld thickness greater than the parent metal plate in butt welds. This feature of a weld is regarded as an imperfection only when the height of the excess weld metal is greater than a specified limit.

Radiographic Image: in the left photo, a high contrast between the density of the image of the parent metal ( darker area ) and the image of the weld ( light area )

Tolerance height of reinforcement or internal protrusion allowed as ASME B31.3:

Inclusions (slag / tungsten)

Size and distribution of rounded indications as ASME BPVC VIII-1 Appendix 4.

Rounded Indications: Indications with a maximum length of three times the width or less on the radiographic are defined as rounded indications. These indications may be circular, elliptical, conical, or irregular in shape and may have tails.

Aligned Indications: A sequence of four or more rounded indications shall be considered to be aligned when they touch a line parallel to the length of the weld drawn through the center of the two outer rounded indications.

Incomplete Fusion

A continuous or intermittent depression in the surface of a weld metal running along its length, due to insufficient weld metal, indicating a thinner than normal section thickness.

Lack of Root Fusion

Lack of fusion between the weld and parent metal at the root of a weld, one side of the root face is not melted.

Incomplete Penetration

Both fusion faces of the root are not melted.
Main causes: excessively thick root face and insufficient root gap

Misalignment

Misalignment between two welded pieces such that while their surface planes are parallel, they are not in the required same plane.

Radiographic Image: An abrupt change in film density across the width of the weld image.

Overlap

An imperfection at the toe of a weld caused by metal flowing on to the surface of the parent metal without fusing to it.

Porosity

Porosity is the presence of cavities in the weld metal caused by gas trapped during welding.

Size and distribution of rounded indications as ASME BPVC VIII-1 Appendix 4.

Rounded Indications: Indications with a maximum length of three times the width or less on the radiographic are defined as rounded indications. These indications may be circular, elliptical, conical, or irregular in shape and may have tails.

Clustered Indications: The illustrations for clustered indications show up to four times as many indications in a local area.

Root concavity

A shallow groove that occurs due to shrinkage at the root of a butt weld.

Do not confuse with incomplete penetration or lack of root fusion that both edge of root face are melt and shrinkage in the middle of root bead.

In case of incomplete penetration or lack of root fusion are un-melt one/both edge of root face.

Undercut

An irregular groove at the toe of a run in the parent metal or in a previously deposited weld metal due to welding. It is characterized by its depth, length and sharpness .