5.1.1 Leaks and ruptures of pipes

The impact of leaking/broken pipes must be taken into account in accordance with the underlying safety strategy for a plant. German RSK guidelines [5], for example, require a leak of 0.1 A (where A is the open cross-sectional area of the pipe in question) to be assumed in relevant pipes, such as main coolant pipes, for example, leading to jet loads and differential pressures in combination with increasing temperatures.

Jet loads are caused by the impact of the oncoming medium, and act as concentrated loads on the structural member involved. They are expressed as load-time functions or as static equivalent load, stating the impact area, load distribution and impact angle. Figure 5.1 shows the idealised function of jet load over time.

Leaks or ruptures in pressurised pipes induce pressures in the spaces affected which act as loads per unit area over time on the structural members and pressure differentials. What has to be taken into account here is how the differential pressures behave over time, as Figure 5.1 shows in idealised form.

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Combined with the jet loads and pressure forces involved, leaking or broken pipes can increase room temperature and hence structural member temperature. The tempera­tures in the structural components affected increase subject to a time delay, so that the temperature curves in those structural members must be recorded to obtain a realistic overlap of the jet loads or differential pressures with their associated temperature effects over time.