Software-based analysis is one of the main methods for detecting and locating a leak from pipelines without the need for extensive instrumentation. However, software-based methods are generally sensitive to process disturbances, which cause the method to fail. In order to deal with these disturbances without increasing the number of measurements, an observer is designed for leak detection in natural gas pipelines as a case study. The proposed design implements a linear unknown input observer with time delays that considers changes of temperature and pressure as unknown inputs and includes measurement noise in the process. The unknown input observer found in the literature is modified for an application of leak detection. Nonisothermal modeling and simulation of a natural gas pipeline with time-variant consumer usage are performed to test the proposed method. Effects of pressure drop and temperature change on observer estimation are simulated and compared to a simulated leak event.

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Software-based methods are common approaches for detecting faults in chemical processes. In this paper, new software-based methodologies were developed for locating multiple leaks in a natural gas pipeline. Two types of multiple leaks, subsequent and simultaneous multiple leaks, from a natural gas pipeline were studied, separately. For both subsequent and simultaneous leaks, case studies with two leak occurrences were demonstrated using MATLAB simulation. For detecting and locating subsequent multiple leaks, an unknown input observer was designed and applied, which was modified from our previous study. New optimization methodology for locating simultaneous multiple leaks was demonstrated. Leak locations were estimated by solving a nonlinear global optimization problem. The global optimization problem contained constraints of partial differential equations, integer, and continuous variables. A new discretization approach was proposed and demonstrated, which required significant less computation effect comparing to conventional global optimization algorithms.

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