The natural gas pipeline network (including distribution network) may be subjected to some extreme conditions such as pipeline rapture, sudden changed demand and etc. The behavior of natural gas pipeline network should be properly identified to prevent network failure and have continued pipeline operation under these extreme conditions. These conditions usually cause unsteady behavior of the pipeline network. Consequently, it is necessary to develop an unsteady state mathematical method to study natural gas pipeline network under unsteady conditions. To achieve this goal, an analytical approach has been developed to analyzed natural gas pipeline network. The governing equations derived for one-dimensional isothermal compressible viscous flow with Kirchhoff's laws have been employed to develop a method for studying the pipeline network under unsteady conditions. The proposed method has been compared with previous studies for validation purposes. The validation shows the proposed method has an average absolute present derivation (AAPD) less than 0.7%. Finally the effect of a few parameters including: friction factor, natural gas composition and decreasing and increasing demand have been studied. Results show that Weymouth and AGA equation predict highest and lowest pressure drop at the network nodes respectively. Also by increasing natural gas molar mass, the pressure at nodes will be decreased. It could be also concluded that demand rise causes pressure drop to decrease and demand fall causes pressure drop to increase.

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