Definition - What does Butt Joint mean?
A butt joint is a welded point of two metallic materials that are joined in the same plane at a 180° angle (i.e., end-to-end).
Butt joints are often prone to excess porosity, increased moisture entrapment, cracking and crevice corrosion due to the containment geometry generated by the angle at which it is formed.
Corrosionpedia explains Butt Joint
Corrosion fatigue is common in butt joints, however butt joints have come into wider use in structural and machine applications.