Hydraulic reliability analysis of an urban loop high-pressure gas network

• Current methods cannot determine the actual flow when a loop network failure occurs.
• A method for determining the actual nodal flow after a failure is presented.
• A better pressure reserve is needed to improve a system's hydraulic reliability.
• Improving the hydraulic reliability of a node may worsen overall system reliability.

Scientific analyses and the provision of practical ways of improving the hydraulic reliability of urban high-pressure gas networks are essential for the safe and stable supply of natural gas by a supplier. A reasonable estimation of the actual obtainable flow for each consumer in the event of a failure is key to the quantitative analysis of hydraulic reliability, which is not an easy task for a loop network. Based on an analysis of the hydraulic characteristics of a loop network, this paper discusses the limitations of existing methods and presents a feasible method for determining the actual nodal flow in a high-pressure gas network loop. This method adopts a process whereby the hydraulic regimes are first analysed according to the designed nodal flow. Next, the nodal pressures are checked, and the actual nodal flow is gradually rectified. Finally, the hydraulic regimes are repeatedly analysed according to the rectified flow until each nodal pressure and each nodal flow satisfy the nodal pressure equations. Moreover, a detailed procedure for a hydraulic reliability analysis of a loop network is presented, and its feasibility is confirmed with an example. The example results show that the network system hydraulic reliability is only 0.879 using the proposed method when pipe 2 fails, whereas the reliability would become 1.0 if using the existing method. The factors affecting the reliability are discussed exhaustively from the aspects of the network system and the consumer, and a number of measures are suggested for improving the hydraulic reliability.