Shown is a titanium tee that cannot have any crevices in which bacteria can grow. This requires both an external and an internal weld. The external weld is completely straightforward but the internal weld is a challenge, not only to weld, but also to photograph.
A simple freehand laser weld. The material is Ti6Al4V and the weld is perfomed under argon coverage. This is a fusion weld (no filler wire added) and the customer supplied the individual parts. Fusion welding like this requires excellent fit of the joint, typically with a gap no bigger than 0.002″
Here is the internal weld, about a half inch down a 0.250″ diameter hole. You can see from the photo that it’s at an awkward angle, so the hole in the upright leg of the tee was made a bit larger in diameter to provide a ledge for the beam to hit. This weld requires no strength; its only function is to seal the crevice to prevent bacterial ingress.