Slag inclusions and lack of fusion are different weld discontinuities, but radiographic appearance can be affected by projection angle, weld geometry, thickness and image quality. The examples below describe general tendencies only; they are not a substitute for qualified interpretation.
Slag inclusions
Slag trapped in a weld may appear as an elongated or irregular indication, sometimes with a shape that follows the weld preparation or bead. Its density and outline vary with composition, orientation, thickness and the direction of the radiation beam. Rounded or mottled appearance is also possible in some circumstances. A single visual feature should not be used to assign a definitive cause.
Lack of fusion
Lack of fusion is a planar condition. It may be difficult to detect when the plane is unfavorably oriented relative to the beam, and may show as a narrow linear feature when the geometry is favorable. Root, sidewall and inter-run locations can project differently. A radiograph can therefore show only a portion of the condition or fail to reveal it clearly.
Separate detection, interpretation and evaluation
First establish that a visible feature is a relevant indication rather than a geometric effect or artifact. Then interpret it using the examination procedure, weld configuration, available views and the examiner’s qualification. Finally, evaluate against the acceptance criteria called up by the contract or governing code. Technique standards and acceptance standards serve different purposes.
When the image is inconclusive
Check identification, coverage, IQI result and image quality. Review other exposures and available manufacturing information. If uncertainty remains, record it and seek the responsible Level III or technical authority; any supplementary method or re-examination must follow approved project controls. Do not infer flaw size or acceptability from a sketch or generic web example.
ISO 17636-1:2022 covers film radiographic techniques for welded joints, but explicitly does not set indication acceptance levels. The applicable evaluation standard and project procedure must be confirmed separately.