IMPORTANCE OF FLAT BOTTOM HOLES (FBH) and SIDE DRILLED HOLE (SDH)
IMPORTANCE OF FLAT BOTTOM HOLES (FBH) and SIDE
DRILLED HOLE (SDH)
Flat-bottom-hole reference blocks have been used as
defect artifact standards in nondestructive testing for many years. Hole making
process can be employ by both conventional machining (drilling) or
non-conventional machining (EDM).
FBH – Flat-Bottomed Hole
and SDH – Side-Drilled Hole are the two main calibration
reflectors which are used in ultrasonic testing. The FBH is drilled into
calibration blocks so that the flat end face presents a circular disc
perpendicular to the beam. The Flat Bottom Hole (FBH) is a smooth planar
reflector, which gives a signal similar to that of a smooth crack or Lack of
Sidewall fusion of similar size. The Flat Bottom Hole (FBH) is also the
practical implementation of the disc-shaped reflectors used to build up the Distance
Gain Size (DGS) / Distance Amplitude Curve (DAC) / Time-Corrected Gain (TCG)
diagram.
However,
any Flat Bottom Hole (FBH) will only be perpendicular to one beam angle and a
different set of Flat Bottom Holes (FBHs) would be needed to calibrate a probe
with a different beam angle. A more versatile reflector is the Side Drilled
Hole (SDH), which is also easier to produce than the Flat Bottom Hole (FBH).
The Side Drilled Hole (SDH) is drilled parallel to the scanning surface and
presents the same reflector to all beam angles. A single calibration block
containing The Side Drilled Holes (SDHs) at different depths can therefore be
used to generate a Distance Amplitude Curve (DAC) for any probe. The diameter
of a Flat Bottom Hole (FBH) or Side Drilled Hole (SDH) is often denoted by the
Ø symbol.