In order to understand and construct a pipe system that will do its job for years, you need to investigate not only the total forces but each one individually. These stressors vary significantly from one another and behave in an ever-changing, dynamic fashion as conditions fluctuate. To improve your knowledge, here are four types of stresses in piping systems.
Axial Stress
First, axial stress accounts for the force along a pipe’s axis (forward or backward). Often, axial loads increase because of hot fluids running through and causing thermal expansion, as long as the pipe has anchoring that creates resistance against this expansion. The best pipe systems have rigidity yet also allow for some expansion, usually via metal expansion joints.
The beauty of an expansion joint is it provides a margin for movement. The reason this is important is this slight displacement lowers the total thermal expansion axial stress because it’s a self-limiting stress. Put simply, as a pipe moves or expands, the existing forces weaken, and the pipe becomes more stable.
Hoop Stress
Second, hoop stress is not one people hear of often. While axial stress proceeds forward or backward along the pipe in a straight line, hoop stress is perpendicular to it, running along the curved edge of the pipe. It originates from internal pressure, which provides this push along the pipe’s circumference. Hoop stress is not self-limiting because internal pressure does not diminish as long as the system is operational. Also, it varies with pipe thickness—the thicker your pipes, the lower your hoop stress tends to be.
Radial Stress
Meanwhile, radial stress also results from internal pressure. Rather than pushing along a curved axis, it pushes outward. The total radial pressure comes from the difference between internal and external pressure.
Fatigue
Fatigue is another type of stress in piping systems. As pipes are in use, they experience repeated pressure fluctuations as well as temperature ramp-ups and cooldowns. These cycles (cycle life is a common metric for determining a pipe’s lifespan) compromise pipe strength over time.
