PIP REEP006 Pump Selection Guidelines

phase is expected to be completed by the end of 2011. The system consists of one raw water intake pump station (IPS), three booster pump stations (BPS 2, 3, and 4), and multiple parallel 2200-millimeter (mm) and 2600-mm diameter pipelines that run approximately 30 kilometers (km) from the Nile River to the newly constructed New Cairo Potable Water Treatment Plant (WTP). Construction will be completed in eight pump installation phases, with design flows ranging from 6 cubic meters per second (m3/sec) at Phase 1 to an ultimate flow of 48 m3 Because the pumping capacity required for Phases 5-8 is to be supplied by a parallel system of pump stations and pipelines that mirror Phases 1-4 (with identical hydraulics and capacities), the following report is based on analysis of Phases 1-4 only. The ultimate flow rate for Phase 4 is 24 m /sec at Phase 8.

It is common practice worldwide for piping designers to route piping by considering mainly space, process and flow constraints (such as pressure drop) and other requirements arising from constructability, operability and reparability. Unfortunately, pipe stress analysis requirements are often not sufficiently considered while routing and supporting piping systems, especially in providing adequate flexibility to absorb expansion/contraction of pipes due to thermal loads. So, when “as designed” piping systems are handed-off to pipe stress engineers for detailed analysis, they soon realize that the systems are “stiff” and suggest routing changes to make the systems more flexible. The piping designers, in turn, make changes to routing and send the revised layout to the pipe stress engineers to check for compliance again. Such “back and forth” design iterations between layout and stress departments continue until a suitable layout and support scheme is arrived at, resulting in significant increase in project execution time, which, in turn, increases project costs. This delay in project execution is further worsened in recent years by increased operating pressures and temperatures in order to increase plant output; increased operating pressures increase pipe wall thicknesses, which, in turn, increase piping stiffnesses further. Such increased operating temperatures applied on “stiffer” systems increase pipe thermal stresses and support loads. So, it is all the more important to make the piping layout flexible at the time of routing.