Penetrant Viscosity

Figure 2-13. Comparison of Dwell Time versus Viscosity for Two Types of Penetrants

TM-1-1500-335-23 Nondestructive Inspection Methods Manual
Page Navigation
118

T.O. 33B-1-1 2.4.5.5.2.5 Penetrant Viscosity. Viscosity has been previously defined as the resistance of a liquid to changing shape. This resistance controls the f low characteristics of a liquid and is a major factor in the time required to enter and fill a void. Viscosity of oils, which includes penetrants, changes drastically with temperature. Oils become thin (less viscous) at high temperatures and thick (more viscous) at low temperatures. Figure 2-12 illustrates how the viscosities of a number of QPL penetrants change with temperature. The horizontal and vertical scales are spaced to show the viscosity changes as a straight line function. The chart shows that the viscosity of a high sensitivity, postemulsifiable (PE) penetrant is about 3 centistokes (cs) at 120^oF (49^oC) and about 75 cs at -10^oF (-23.4^oC), or becomes about 25 times thicker. The viscosity of visible dye is about 2 cs at 120^oF (49^oC) and 22 cs at -10^oF (-23.5^oC), which is an eleven times increase in viscosity. See ASTM D341-43 for viscosity of several QPL Penetrants. Figure 2-12. Viscosity of Several QPL Penetrants at Various Temperatures 2.4.5.5.2.5.1 The part temperature range for applying penetrants is 40^oF (4^oC) to 120^oF (49^oC). Actually, most penetrants are applied at or near a part temperature of 70^oF (21.1^oC). Therefore, nearly all operating instructions or procedures specifying dwell times are based on applying penetrant to a part that is at or near a temperature of 70^oF (21.1^oC). For high sensitivity PE penetrant, Figure 2-13 shows that the viscosity (7 cs) at 70^oF (21.1^oC) is twice the viscosity (14 cs) 2-42 Change 2

Privacy Statement
Press Release
Contact