Why is Radial Stress Neglected?

For thin-walled piping, design codes like the ASME B31.3 and the EN 13480 only specify requirements for the hoop and the axial stresses, whilst the radial stress is ignored. Why is this?

As the pipe is in equilibrium, the radial stress on the inside of the pipe wall will be equal to the internal pressure and the stress on the outside of the pipe wall will be equal to the ambient pressure. The radial stress through the pipe wall is given by Lamé’s Theorem which shows that the radial stress though the pipe wall is inversely proportional to the radius squared. Consequently, the maximum radial stress in the pipe wall is equal to the internal pressure.

As shown in the figure below it is seen that the hoop and axial stress are also proportional to the internal pressure (Pi). However, these include a second factor which for thin-walled piping is always far larger than 1, meaning that the radial stress will always be far smaller than the axial and hoop stresses.

Discover the learning path “Pipe Stress Analysis according to ASME B31.3 and EN 13480” to gain a deeper understanding of the theory, design codes and methodologies for pipe stress analysis and enhance engineering judgement.