Varian Linatron High-Energy X-ray Applications 2007

Grain Radiography Coverage Requirements. Contrast
sensitivities of better than 1% can be achieved routinely
with the Linatron using optimum radiographic production
techniques. Defects such as voids and gross density
variations in the solid propellant are readily detected at that
sensitivity. The simplest radiographic procedure (e.g., one
exposure through the grain or two exposures, one at 0˚ and
the second at 90˚ may be used when these are the only
concern. However, cracks and separations are also of great
concern in rocket motors.
Cracks with widths of 1 to 5 mils (0.03 - 0.13 mm) are
detected only when they are aligned with the radiation
source. Most propellants with cracks will open to a width
of 10 to 30 mils (0.25 - 0.76 mm) minimum. At these
widths cracks can readily be detected at almost any angle to
the radiation, and through large thicknesses of propellant.
FIGURE 5-7. Visualization of crack-like defects, as a function of
propellant thickness and crack angle, for x/x = 0.2%.
Figure 5-7 illustrates the width of crack-like defects that
can be demonstrated through various thicknesses of
propellant, at various projection angles, with an assumed
contrast sensitivity of 0.2%. Refer to the approximate
relationship Δx = W/ø. It can be seen from Figure 5-7, as
propellant thickness increases, the ratio W/ø increases,
which means that the same width crack will be shown at
smaller angles. For example,
page 50
Propellant Thickness Ratio of Crack Width
to Projection Angle
inches cm
Varian Linatron applications
30-36 76.2 - 91.4 W/ø ≈ 1.0
40-50 101.6 - 127.0 W/ø ≈ 1.5
50-60 127.0 - 152.4 W/ø ≈ 2.0
To observe the required rocket grain cracks, the number of
exposures must be increased as the diameter increases. If
the technique being used produces contrast sensitivity
other thanAx/x = 0.2%, the procedures must be modified
accordingly to obtain an equivalent defect detectability.
Tangential Radiography. Propellant-to-insulation (liner
separations) in the domes are considered critical defects
wherever they occur in a rocket motor. Separations as small
as 2 mils (0.05 mm) can be shown on the radiograph,
when the separation occurs at the tangential point.
FIGURE 5-8. Probability (P) of detecting propellant to insulation
separation versus number of exposures (N) for various circumferential
lengths of separation (Lc , for 54-inch (137 cm) diameter (D),
rocket motor, P = Lc/n - D N.