In this article, we will discuss how the design of the gas distribution network influences safety procedures and blowdown times. CRIGEN, a Research Center of GDF SUEZ R&I Division, has developed a tool that helps GrDF, Gaz Réseau Distribution France (main French gas distribution operator) analysts to optimize the equipment of the gas network and its structure by drawing up the valve scheme. We will focus on the operating principle of the tool, which is based on the representation of the gas network in the form of a specific graph - a dual graph, which is easily computed. It isolates on the one side the basic structure involved when blowdown occurs, and on the other side, the valves. The relation between each node of that graph is then studied in order to devise effective solutions for decreasing blowdown time by closing specific valves. This software thus helps the analysts to audit their network, pointing out potential weaknesses, and offering them solutions in order to decrease the network's blowdown time.

1 Introduction

GrDF is the main French gas distribution operator: It provides gas to 9,200 municipalities, mainly big cities. GrDF operates and maintains a network of over 118,000 miles of pipelines and supplies 11 million customers. Due to the complexity and density of the network, one of the major issues for the distribution company is safety.

2.1 Background to an intervention

To gain a clear understanding of the issues arising from the design of the gas network, we will first set out the operational stages leading up to the securing of the gas network. The operator's objective is to blowdown the portion of the network affected so as to reduce pressure to a few psig and to begin repairs to the pipes.

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