A Nelder–Mead algorithm-based inverse transient analysis for leak detection and sizing in a single pipe

Abstract In this paper the results of an experimental validation of a technique for leak detection in polymeric pipes based on the inverse transient analysis (ITA) are presented. In the proposed ITA the Nelder–Mead algorithm is used as a calibration tool. Experimental tests have been carried out in an intact and leaky high-density polyethylene (HDPE) single pipe installed at the Water Engineering Laboratory (WEL) of the University of Perugia, Italy. Transients have been generated by the fast and complete closure of a valve placed at the downstream end section of the pipe. In the first phase of the calibration procedure, the proposed algorithm has been used to estimate both the viscoelastic parameters of a generalized Kelvin–Voigt model and the unsteady-state friction coefficient, by minimizing the difference between the numerical and experimental results. In the second phase of the procedure, the calibrated model allowed the evaluation of leak size and location with an acceptable accuracy. Precisely, in terms of leak location the relative error was smaller than 5%

The synergistic effects of hydrogen embrittlement and transient gas flow conditions on integrity assessment of a precracked steel pipeline

We are reporting in this study the hydrogen permeation in the lattice structure of a steel pipeline designed for natural gas transportation by investigating the influence of blending gaseous hydrogen into natural gas flow and resulted internal pressure values on the structural integrity of cracked pipes. The presence of cracks may provoke pipeline failure and hydrogen leakage. The auto-ignition of hydrogen leaks, although been small, leads to a flame difficult to be seen. The latter makes such a phenomenon extremely dangerous as explosions became very likely to happen. In this paper, a reliable method is presented that can be used to predict the acceptable defect in order to reduce risks caused by pipe failure due to hydrogen embrittlement. The presented model takes into account the synergistic effects of transient gas flow conditions in pipelines and hydrogen embrittlement of steel material due to pressurized hydrogen gas permeation. It is found that blending hydrogen gas into natural gas pipelines increases the internal load on the pipeline walls due to overpressure values that may be reached in a transient gas flow regime. Also, the interaction between transient hydrogen gas flow and embrittlement of API 5L X52 steel pipeline was investigated using Failure Assessment Diagram (FAD) and the results have shown that transient flow enhances pipeline failure due to hydrogen permeation. It was shown that hydrogen embrittlement of steel pipelines in contact with the hydrogen environment, together with the transient gas flow and significantly increased transient pressure values, also increases the probability of failure of a cracked pipeline. Such a situation threatens the integrity of high stress pipelines, especially under the real working conditions of hydrogen gas transportation

The synergistic effects of hydrogen embrittlement and transient gas flow conditions on integrity assessment of a precracked steel pipeline

We are reporting in this study the hydrogen permeation in the lattice structure of a steel pipeline designed for natural gas transportation by investigating the influence of blending gaseous hydrogen into natural gas flow and resulted internal pressure values on the structural integrity of cracked pipes. The presence of cracks may provoke pipeline failure and hydrogen leakage. The auto-ignition of hydrogen leaks, although been small, leads to a flame difficult to be seen. The latter makes such a phenomenon extremely dangerous as explosions became very likely to happen. In this paper, a reliable method is presented that can be used to predict the acceptable defect in order to reduce risks caused by pipe failure due to hydrogen embrittlement. The presented model takes into account the synergistic effects of transient gas flow conditions in pipelines and hydrogen embrittlement of steel material due to pressurized hydrogen gas permeation. It is found that blending hydrogen gas into natural gas pipelines increases the internal load on the pipeline walls due to overpressure values that may be reached in a transient gas flow regime. Also, the interaction between transient hydrogen gas flow and embrittlement of API 5L X52 steel pipeline was investigated using Failure Assessment Diagram (FAD) and the results have shown that transient flow enhances pipeline failure due to hydrogen permeation. It was shown that hydrogen embrittlement of steel pipelines in contact with the hydrogen environment, together with the transient gas flow and significantly increased transient pressure values, also increases the probability of failure of a cracked pipeline. Such a situation threatens the integrity of high stress pipelines, especially under the real working conditions of hydrogen gas transportation

Hygrothermal Behavior of a Washing Fines-Hemp Wall under French and Tunisian Summer Climates: Experimental and Numerical Approach

International audienceThis study experimentally and numerically investigates the hygrothermal behavior of a wall made of washing fines hemp composite under typical French and Tunisian summer climates. Actually, insulating bio-based building materials are designed in order to reduce energy and non-renewable resources consumptions. Once their multiphysical properties are characterized at material scale, it is necessary to investigate their behavior at wall scale. Washing fines hemp composite shows low thermal conductivity and high moisture buffer ability. The test wall is implemented as separating wall of a bi-climatic device, which allows simulating indoor and outdoor climates. The numerical simulations are performed with WUFI Pro 6.5 Software. The results are analyzed from the temperature, relative humidity and vapor pressure kinetics and profiles and from heat and moisture transfer and storage. The thermal conductive resistance calculated at the end of the stabilization phase is consistent with the theoretical one. The hygric resistance is consistent for simulation up to steady state. The dynamic phase under daily cyclic variation shows that for such cycles two thirds of the thickness of the wall on the exterior side are active. It also highlights sorption-desorption phenomena in the wall

Modeling and simulation of PE100 pipe response under transient events caused by pump failure

In this work, the response of a PE100 pipe under transient events following pump failure is numerically investigated. The developed numerical model was based on the generalized Kelvin-Voigt model and the Vitkovsky et al. formulation. The method of characteristics (MOC) was used for numerical discretization. The relevance of an unsteady friction term in the pressure wave damping was analyzed. Pressure and circumferential stress responses indicated high rates in the pressure waves damping for the PE100 pipe. Through a parametric study, it was shown that the HDPE pipe may serve in damping and dispersing pressure waves without the need for additional protection devices

Effect of integrating polymeric pipes on the pressure evolution and failure assessment in cast iron branched networks

International audiencePressure response and structural integrity assessment of cast iron and HDPE pipes were investigated in this study. The failure analysis of pipes in a branched network was considered taking into consideration the maximum stress generated by hydraulic transient events and the presence of an initial external semi-elliptical defect. The numerical study was conducted based on a developed non-conventional transient solver that incorporates the viscoelasticity of polymeric pipes. Considering the replacement of pipes located in sensitive zones with high-density polyethylene (HDPE) pipes, the pressure evolution of the network was evaluated for different network states at different locations. The integration of polymeric pipes in the originally cast-iron network provided remarkable pressure wave damping and dispersing in some locations. Since the failure of pipes with a corrosion crater is likely to occur when the admissible stress is reached, a structural integrity analysis was conducted. Failure Assessment Diagram (FAD) using the SINTAP code was considered to calculate the safety factors for cast iron pipes with different metallic-plastic combinations, whereas a semi-empirical model that calculates the J-integral is used for HDPE pipes. The results of this study conclude that high attention should be paid when a longitudinal crack is located in the pipelines. It may be possible for integrated polymeric pipes to alleviate the risk of failure in the network. However, under large crack geometries, additional measures should be taken