What factor can lead to insufficient penetration of the liquid penetrant into defects?

The insufficient penetration of liquid penetrant into defects primarily relates to the geometry of the defect. When a defect has complex shapes, such as sharp corners or varying depths, it can hinder the liquid penetrant from adequately entering all areas of the defect. This could lead to incomplete inspection results, as the penetrant may not be able to fill small cracks or intricate patterns effectively.

Surface cleanliness, while important in ensuring the penetrant can access the defect, is not as directly impactful on the penetration of the liquid into the defect itself as defect geometry is. The time of exposure can affect the outcome of the inspection, but it primarily influences the amount of penetrant that can seep into the defect rather than how the geometry might impede that process. Similarly, the temperature of the penetrant can affect its viscosity and ability to flow, but again, these factors are secondary to how the shape and structure of the defect itself can prevent penetration. Thus, the geometry is the most decisive factor in whether or not the penetrant will effectively enter and fill the defect.