Definition - What does Radial Stress mean?
Radial stress in a pipe can be defined as the effective stress acting in the radial direction i.e. the direction perpendicular to the longitudinal axis of the pipe. The stress acts in the radial direction, which is why it's known as radial stress. The hoop stress, longitudinal stress and radial stress act mutually perpendicular to each other. In buried pipes, these different stresses act on the pipe depending on the loading, and fluid characteristics.
Trenchlesspedia explains Radial Stress
If the pressure is acting from inside the cylinder, the maximum stress develops at the inner surface and the minimum stress will develop at the outer surface. Similarly if the pressure is acting from outside the pipe, the maximum stress will develop at the outer surface and the minimum stress will develop at the inner surface. Radial stress is represented by σr. For thin pipes, the value of radial stress is much less compared to the hoop and longitudinal stresses acting on a pipe and therefore is often neglected.