This paper describes the most important results of a theoretical, experimental and in situ investigation developed in connection with a water supply pumping pipeline failure. This incident occurred after power failure of the pumping system that caused the burst of a prestressed concrete cylinder pipe (PCCP). Subsequently, numerous hydraulic transient simulations for different scenarios and various air pockets combinations were carried out in order to fully validate the diagnostic. As a result, it was determined that small air pocket volumes located along the pipeline profile were recognized as the direct cause of the PCCP rupture. Further, a detail survey of the pipeline was performed using a combination of non-destructive technologies in order to determine if immediate intervention was required to replace PCC pipes. In addition, a hydraulic model was employed to analyze the behavior of air pockets located at high points of the pipeline.
This paper presents a case study of an existing water pipeline with five pumping stations each equipped with five pumps. In order to study the pipeline behavior prior to putting the system into operation, several transient simulations for different scenarios were developed. Results revealed that the most serious situation occurred when a simultaneous failure of the five pumps occur at each station caused by power cut, producing negative pressure waves because the system for control of hydraulic transients of the pipeline was insufficient to suppress downsurge pressures, due to the moment of inertia of all the pumps being erroneously considered during the design stage. The necessity to start supplying water to the population led to attempt an unconventional form of protecting the line against low pressures. The solution was to operate two of the five pumps per plant, and permit air to enter through combination air valves located along the pipeline. Air entrained formed pockets that remained stationary at the air valves locations, acting as air cushions that absorbed the energy of transient pressure waves. Computational simulations were conducted considering that two pumps are in operation at each plant and suddenly these fail simultaneously caused by power failure. The program was verified by comparing the calculated results with those registered during field pressure measurements. It was noticed that the surge modelling results are in good agreement with the measured data; furthermore, these show the air pockets in combination with existing devices for transient control protect the system adequately, avoiding potential damage to the pipeline.
Este trabajo representa una contribución para evaluación de las condiciones de las redes de observación de la precipitación en un área urbana, a partir de la comparación entre una red de sensores de disdrómetros ópticos láser (DOL) y una red de pluviómetros de balancín (PB) en la Ciudad de México. En la metodología se seleccionaron 9 estaciones DOL y 16 estaciones PB, las cuales secompararon de dos formas: primero, a partir de la acumulación total de precipitación durante tres años y segundo, por eventos de tormenta. Los resultados indican, que el análisis por eventos de tormenta es más representativo que comparando la precipitaciónacumulada. Las mediciones son aceptables, ya que estas se comprobaron a partir de correlaciones lineales. Asimismo, se determinó que el número de eventos y la distancia entre las estaciones contribuyen en la correlación de las mediciones. Es deseable que la metodología se aplique en el control de calidad periódico de las mediciones (calibración) y sea parte de las buenas prácticas parala medición del ciclo hidrológico urbano a escala local.
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