Pluvinage C Schmitt and E Hadj Taeib

1 Laboratoire de Fiabilité Mécanique (LFM), Ecole Nationale d'Ingénieurs de Metz, Ile du Saulcy, 57045 Metz, France

2 Applied Fluid Mechanics Dept., Ecole Nationale d'Ingénieurs de Sfax, BP W 3088 Sfax, Tunisia

Abstract. A numerical model has been created to simulate the propagation of pressure waves in water networks. The model takes into account the structure of the water network and the pressure loss. When several valves are closed simultaneously, pressures can exceed the admissible pressure and cause failure. In this case, the severity of a defect such as a corrosion crater (pit) has been estimated by computing a safety factor for the stress distribution at the defect tip. To investigate the defect geometry effects, semi-spherical and semi-elliptical defects are assumed to exist up to one half thickness of the pipe wall. The results have been input into the Structural Integrity Assessment Procedure (SINTAP) Failure Diagram Assessment (FAD) to obtain the safety factor value. Conventionally, it is considered that the failure hazard exists if this safety factor is less than two.

Keywords: Water network, water hammer, pipe, failure, corrosion, safety factor 1. Introduction

Most water distribution systems in the world are older than 30 years. The outdatedness of the installations and the poor quality of the pipe materials, which are often corroded or damaged, are responsible for failures. Consequently, a large amount of water is lost by leaks, often more than 30%. Leakage occurs in many components of the distribution system: pipes, service connections, valves or joints. Leaks and failures are a major economic problem. When internal pressure decreases, leaks can also serve as pathways for contamination by harmful organisms from outside the pipes and pathogen intrusions can have health consequences.

Hence, programs have been developed to evaluate the degradation state and the risk of failure of pipe systems and to plan their rehabilitation. Preventive and predictive maintenance strategy programs with systems for inspection and control are developed (Sœgrov et al., 1999; Hunaidi et al., 2000; Rajani and Kleiner, 2002). Leakage and cracking of pipes results from the initiation and propagation of defects. Initial defects can be assumed to be:

* To whom correspondence should be addressed. e-mail: [email protected]

(a) corrosion pitting or (b) mechanical damage, e.g., scratches and gouges, occurring during pipeline construction or during in-service maintenance. Variations in internal pressure may be caused by soil-movement induced bending or repeated loading from road traffic. Failure occurs when the defect has reached its critical size.

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