Natural gas pipelines employ automatic safety devices to close valves and prevent the release of gas in the event of a pipeline break. These systems are critical to safe, economic operation of the pipelines. This paper examines the application of two primary break detection systems and their interaction with other pipeline protection systems. A pipeline break causes a pressure drop. But the nature of this drop is complicated by multiple factors, including: diameter and length of the pipeline, dimension of the break, temperature and pressure of the gas, and flow rate. In addition, detection and response is difficult because the valve actuators and line break devices are dependent on their distance from the break point and the resulting pressure drop. The complexity is also increased by normal pipeline operations that result in pressure drops unrelated to a break. These fluctuations can be caused by changes in the operation of compression stations or by increased gas consumption by branches and users. A very reliable way to identify a pipeline break is to detect the “abnormal” value of the rate of pressure drop (DP/DT) relative to values established during the normal operation of the pipeline.
The paper addresses the two main types of line break detection systems: gas- and electric-operated.
Gas-operated systems (without electronic transducers) sense the pressure drop rate or level mechanically with pneumatic components logic. All the energy is supplied by the transmitted flow and can be stored in tanks Electronic devices employ a pressure transducer to continuously sense the line. A microcontroller records the data and triggers a solenoid valve to move the isolation valve. The small amount of energy required can be provided by lithium battery packs or alternative power supply such as a solar panel, thermoelectric generator, or fuel cells. These leakage detection systems can work standalone or combined as a part of a SCADA system that may also include wire, pressure profile, optical fiber systems. Understanding the operation of these systems, the factors affecting their measurements, and interaction with other aspects of the system is critical to safer, more economic pipeline operations.