What Is Piping Stress Analysis?

 

Piping stress analysis involves using software to help you determine how much internal forces and moments, stresses, and displacements are produced by your piping system in specific loading conditions. You can then use those results to verify that all key parameters (stresses, nozzle loads, support load, etc.) stay within their specified limits in every possible combination of operating scenarios.

The piping stress analysis is the most important part of the design process for any new plant or re-design of an existing one. It helps ensure that the piping system is Piping stress analysis sound and capable of handling all types of expected loads, whether static or dynamic.

A piping stress analysis begins with a geometrical description of the piping structure and its components. From there, the analysis considers the maximum and typical forces that are likely to be applied to the pipe and its attached equipment. Then it calculates the internal forces and moments, stresses, displacements, and flange loads at each point in the system under those loading conditions. This is usually done using a software program such as CAESAR II.

Most of the stresses that occur in a piping system are sustained, meaning they are present continuously throughout operation. Examples include pressure and weight, but they can also be caused by axial loads from flanges, valves, or other equipment attached to the piping. Those axial forces must be balanced by internal and external forces and moments to keep the piping system in equilibrium. Exceeding the sustained allowable stresses could lead to catastrophic failure of the piping.

Other types of piping stresses are transient in nature. They may be the result of dynamic events such as water hammer, relief valve discharge, or seismic activity. Or, they can be due to changes in fluid flow velocity or temperature that cause thermal expansion and contraction of the piping. The piping must be designed to be able to handle these stresses without damaging or rupturing the pipe.

Once you have determined the most probable stresses that your piping system will experience, it's time to compare those to the maximum or recommended values set by the codes. You must verify that the calculated stresses, nozzle loads, support loads, and displacements are not excessive in any of the different operating scenarios.

Some of the factors to consider are:

The piping must be capable of resisting all types of load conditions that may be encountered during its life cycle. Some of these are governed by the code and others are not. For example, the piping must be able to withstand the axial stress of internal pressure and the torsional stress of mechanical vibrations in a vessel. Occasional loads may be the wind or seismic acceleration that is defined by the building code for which your plant has to comply. Other occasional loads include the weight of a load, and the deadweight of the piping itself and its accessories such as flanges and supports. Then there are the flanged connections, which should be leak-proof and withstand a buckling load.