Slag Inclusion
Slag inclusion is a non-metallic solid trapped in the weld metal during shielded-metal-arc or flux-cored welding, typically from incomplete inter-pass cleaning, appearing as irregular dark indications on a radiograph.
Definition
Slag inclusions are volumetric flaws produced when molten slag from a previous pass is not removed before the next pass deposits weld metal over it. They reduce cross-section and can initiate fatigue cracking but are generally less severe than planar flaws.
Related terms
- Porosity — Porosity is a volumetric weld defect consisting of gas-filled cavities trapped in the solidifying weld pool, classified as scattered, clustered, linear, or piping (wormhole) porosity depending on distribution and morphology.
- Crack — A crack is a linear discontinuity in a material with negligible opening width, resulting from stress, fabrication, or in-service damage, and is the most safety-critical defect type in pressure equipment and structures.
- Lack of Fusion (LoF) — Lack of fusion is a weld defect in which the deposited weld metal fails to fuse with the base metal or with the previous weld pass, producing a planar discontinuity along the fusion boundary.
Further reading
weld defect classification and detection methods
More defect terms
Lack of Penetration · Undercut · Overlap · Burn-Through · Weld Spatter · Lamination · Lamellar Tearing · Hydrogen-Induced Cracking · Stress Corrosion Cracking · Sulfide Stress Cracking
Where this comes up in practice
Terms like this one appear in three places that matter commercially: the written practice that governs how your personnel are qualified, the procedures and technique sheets that define how an examination is actually performed, and the evidence an auditor or client asks for when they want to know why an inspection was accepted. Getting the terminology right is the easy part; being able to produce the qualification record, the calibration traceability and the procedure revision that applied on the day of the inspection is the part that decides audits.
Atlantis NDT provides NDT training and certification against ASNT SNT-TC-1A and ISO 9712, ASNT Level III consulting for written practices and procedure approval, inspection management software that holds qualification, calibration and procedure-revision evidence in recoverable form, and an asset integrity platform that binds inspection results to the asset they describe. Browse the full NDT glossary or ask a Level III directly.