#ndt The “Mum-Flower”-Type Array Probe (via Immersion) adopts a 45-degree-tilted cone screen to make orthogonal shift of the beam into a ring of a pipe either from inside or outside, thus ending up fully covering either the inner surface or the outer surface of the pipe wall.
The ring interface can be placed onto one end of a threaded bolt to make full coverage of the circle, with graphic scanning to judge the flaws visually, as an ideal substitute for conventional measure.

1. The “plane-ring
Source: NDT