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.
Definition
LoF results from inadequate heat input, contaminated joint faces, incorrect electrode angle, or improper torch manipulation. It is a planar flaw similar in mechanical effect to a crack and is universally rejected by code.
Detection
LoF is best detected by angle-beam UT and PAUT; RT detection depends strongly on flaw orientation relative to the beam.
Related terms
- Lack of Penetration (LoP) — Lack of penetration is a weld defect in which the weld root fails to extend completely through the joint thickness, leaving an unfused area at the root face.
- 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.
- 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.
Further reading
weld defect classification and detection methods · weld inspection acceptance criteria aws vs asme
More defect terms
Porosity · 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.