Density
or Specific Gravity
The density or specific gravity of a penetrant
material has a slight to negligible effect on the performance
of a penetrant. The gravitational force acting on the penetrant
liquid can be working either with or against the capillary
force depending on the orientation of the flaw during the dwell
cycle. When the gravitational pull is working against the capillary
rise, the strength of the force is given by the following equation:
Force = pr^{2}hpg
Where:
r = radius of the crack opening
h = height of penetrant above its free surface
p = density of the penetrant
g = acceleration due to gravity
When the direction of capillary flow is in the same direction
as the force of gravity, the added force driving the penetrant
into the flaw is given by the formula shown below:
Force = hAp
Where:
h = height of penetrant above its free surface
A = crosssectional area of the opening
P = density of the penetrant
Increasing the specific gravity by decreasing the percent
of solvent (by volume) in the solution will increase the penetration speed.
Reference:
Tugrul, A. B., Capillarity Effect Analysis for Alternative Liquid
Penetrant Chemicals, NDT & E International, Volume 30 Number
1, Published by Elsevier Science Ltd., Oxford England, February
1997, pp. 1923.
