Welding Defects - QC Notes - QCSKILL

Welding Defects – QC Notes

Post author:QC-SKILLS
Post published:June 30, 2020
Post category:Mechanical / OIl & Gas / Oil & Gas Engineering / QA/QC / QA/QC Systems / Welding

Cold Lap

Cold Lap is a condition where the weld filler metal does not properly with the base metal or the previous weld pass material (inter-pass cold lap). The arc does not melt the base metal sufficiently and causes the slightly molten puddle to flow into the base material without bonding

Porosity

Porosity is the result of “gas entrapment” in the solidifying metal. Porosity can take many shapes on a radio-graph but often appears as dark round or irregular spots or specks appearing singularly, in clusters, or in rows. Sometimes, porosity is elongated and may appear to have a tail. This is the result of gas attempting to escape while the metal is still in a liquid state and is called “wormhole porosity” All porosity is a void in the material and it will have a higher radio-graphic density than the surrounding area.

Cluster Porosity

Cluster Porosity is caused when flux coated electrodes are contaminated with moisture. The moisture turns into gas when heated and becomes trapped in the weld during the welding process. Cluster porosity appears just like regular porosity in the radio-graph but he indications will be grouped close together.

Slag Inclusion

Slag inclusions are non metallic solid material entrapped in weld metal or between weld and base metal. In a radio-graph, dark, jagged asymmetrical shapes within the weld or along the weld joints areas are indicative of slag inclusions.

Incomplete Penetration (IP) or lack of penetration (LOP)

Incomplete Penetration (IP) or lack of penetration (LOP) occurs when the weld metal fails to penetrate the joint. It is one of the most objectionable weld discontinuities. Lack of penetration allows a natural stress riser from which a crack may propagate. The appearance on a radio-graph is a dark area with well defined, straight edges that follows the land or root face down the center of the weldment.

Incomplete fusion

Incomplete fusion is a condition where the weld filler metal does not properly fuse with the base metal. Appearance on radio-graph is usually appears as a dark line or lines oriented in the direction of the weld seam along the weld preparation or joining area.

Internal Concavity or Suck Back

Internal concavity or suck back is a condition where the weld metal has contracted as it cools and has been drawn up into the root of the weld. On a radiograph it looks similar to a lack of penetration but the line has irregular edges and it is often quite wide in the center of the weld image.

Internal or Root Undercut

Internal or Root Undercut is an erosion of the base metal next to the root of the weld. In the radio-graphic image it appears as a dark irregular line offset from the center-line of ht weldment. Undercutting is not as straight edged as LOP because it does not follow a ground edge.

External or Crown Undercut

External or Crown Undercut is an erosion of the base metal next to the crown on the weld. In the radio-graph, it appears as a dark irregular line along the outside edge of the weld area.

Offset or Mismatch

Offset or Mismatch are terms associated with a condition where two pieces being welded together are not properly aligned. The radiographic image shows a noticeable difference in density between the two pieces. The difference in density is caused by the difference in material thickness. The dark, straight line is caused by the failure of the weld metal to fuse with the land area.

Inadequate Weld Reinforcement

Inadequate Weld Reinforcement is an area of a weld where the thickness of weld metal deposited is less than the thickness of the base metal. It is very easy to determine by radiograph if the weld has inadequate reinforcement, because the image density in the area of suspected inadequacy will be higher (darker) than the image density of the surrounding base material.

Excess Weld Reinforcement

Excess Weld Reinforcement is an area of a weld that has a weld metal added in excess of that specified by engineering drawings and codes. The appearance on a radiograph is a localized, lighter area in the weld. A visual inspection will easily determine if the weld reinforcement is in excess of that specified by the engineering requirements.

Cracks

Cracks can be detected in a radiograph only when they are propagating in a direction that produces a change in thickness that is parallel to the x-ray beam. Cracks can appear as jagged and often very faint irregular lines. Cracks can sometimes appear as “tails” on inclusions or porosity.

Discontinuities in TIG Welds

Tungsten Inclusion

Tungsten inclusion: Tungsten is a brittle and inherently dense material used in the electrode in tungsten inert gas welding. If improper welding procedures are used, tungsten may be entrapped in the weld. Radio graphically, tungsten is more dense than aluminum or steel, therefore it shows up as a lighter area with a distinct outline on the radiograph

Oxide Inclusion

Oxide Inclusions are usually visible on the surface of material being welded (especially aluminum). Oxide inclusions are less dense than the surrounding material, and, therefore appear as dark irregularly shaped discontinuities in the radiograph

Discontinuities in TIG Welds

Whiskers are short lengths of weld electrode wire, visible on the top or bottom su6rface of the weld or contained within the weld. On a radiograph they appear as light, “wire like” indications.

Burn Through

Burn Through results when too much heat causes excessive weld metal to penetrate the weld zone. Often lumps of metal sag through the weld, creating a thick globular condition on the back of the weld. These globs of metal are referred to as icicles. On the radiograph, burn through appears as dark sports, which are often surrounded by light globular areas (icicles).

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