A Conundrum – The Difficulties of Pipe Stress Analysis for Cold Pipes

It is often argued that ambient temperature piping systems do not require pipe stress analysis. This may be true up to a point – where good engineering practice is followed and the piping systems have a generous amount of flexibility. However, there are aspects of cold water piping design that do require an analysis of the stresses in the piping system and the loads generated by the pipework.

In particular, pump stations need to be properly engineered to manage pump nozzle loads. High nozzle loads can cause misalignment of pump and motor and cause wear and vibration. Also, in the New Zealand context, the significant loads arising from seismic action need to be controlled. It is essential that any pump can withstand these loads without significant damage.

This paper looks at the design of cold water pipework with a focus on pump station design. Case studies illustrate some of the issues that arise in pipe stress analysis of cold water systems and how to resolve these. The importance of developing an appropriate flexibility concept at the preliminary design stage is described. In particular, it discusses the difference between high temperature piping and cold water piping and why the latter often requires a more complex analysis.