What aspect does excessive stress on tubing typically affect?

Excessive stress on tubing primarily affects its integrity. This refers to the tubing's ability to withstand various forces without compromising its structural strength. When tubing is subjected to stress beyond its designed capacity—such as from high pressure, bending, or thermal expansion—it can experience deformation, cracking, or even complete failure. This degradation can lead to leaks, which are critical concerns, especially in applications such as aircraft systems where reliability and safety are paramount.

The other choices address different aspects but are not directly impacted by stress on the tubing itself. Fluid viscosity relates to the thickness of the fluid and how easily it flows but is not influenced by tubing stress. Fitting compatibility concerns the proper matching of components to connect effectively, which does not relate to tubing integrity issues. Air temperature, while relevant in other contexts, does not directly relate to the physical stress on the tubing materials.