System Experience & Training # 1998 Gothenburg
Thanks to a number of beneficial properties, plastics pipes are widely used in the construction of pipelines. Very low absolute roughness, high wall resistance to aggressive agents (contained 111 soil and in the liquid stream) and simple assembly cause these pipelines to be cost-effective both in construction and operation.
The hydraulic work conditions of pipelines, including those made of plastics pipes, are generally tested and assessed for a stationery flow of stream. From the water distribution point of view this is undoubtedly the main concern. On the other hand, however, the pipeline's durability and resistance to extraordinary conditions also form an important aspect of the pipeline's operation. Extraordinary conditions result from an unsteady flow, i.e., a variable flow of stream in time. Unsteady conditions arise during network start-up (ex., when filling the pipes with liquid) as well as during pipeline operation. Occasionally, the variable flow of water in the pipeline operating under pressure may assume the form of water hammer.
Unsteady flows can be dangerous for all pipes. These phenomena are still under investigation. The maximum pressure increase and pressure wave velocity, calculated by engineers. should include the pipe wall elasticity, which is in dynamic conditions, variable in time. This specifically refers to plastics pipes.
In order to further investigate the phenomena associated with unsteady water flows, experimental studies have been undertaken. The experiments utilized commonly applied pipes such as u-PVC. MDPE and HDPE. For comparative purposes the tests also included flows in steel pipes.