AWS Certified Welding Inspector — FundamentalsNondestructive Examination (NDE)Medium
A CWI is evaluating a radiographic film that shows several small, rounded indications randomly distributed throughout the weld bead. These indications are darker than the surrounding weld metal. What type of discontinuity do these most likely represent?
- APorosity
- BTungsten inclusions
- CSlag inclusions
- DIncomplete penetration
Show answer & explanationAnswer & explanation
Correct answer: A. Porosity
Small, rounded, randomly distributed, and darker indications on a radiograph are characteristic of porosity. Porosity represents gas bubbles trapped in the weld metal, which are less dense than the surrounding material, allowing more radiation to pass through and resulting in darker spots on the film. Slag and tungsten inclusions are typically irregular or very bright (for tungsten), while incomplete penetration is a linear dark indication.
Why the other options are wrong
- B. Tungsten inclusions are very dense and appear as very bright (light) spots on the radiograph.
- C. Slag inclusions are typically irregular in shape and appearance, not rounded.
- D. Incomplete penetration appears as a continuous or intermittent dark line along the weld root.
RT Porosity Indication
On a radiograph, porosity appears as small, dark, rounded or elliptical indications, often randomly distributed, due to gas entrapment within the weld metal.
- Less dense than surrounding material, allowing more radiation passage.
- Can be isolated, clustered, or uniformly scattered.
- Shape helps differentiate from other volumetric discontinuities like slag.
Memory trick: Round dark spots mean gas, bright spots mean heavy mass.