Abstract
Pigging in pipelines basically performs operations for five reasons including cleaning the pipe interior, batching or separating dissimilar products, displacement, measurement, and internal inspection. A model has been proposed for the dynamic simulation of the pigging process after water pressure testing in a long slope pipeline. In this study, an attempt has been made to analyze two serious accidents during pigging operation in 2010 by the model which is developed by the method of characteristic (MOC) by Wylie et al. (1993) and the two-phase homogeneous equilibrium vaporous cavitation model deveoped by Shu (2003) for vaporous cavitation. Moreover, simulation results of the third operation show good agreement with field data from the previous field trial. After investigation, it was showed that the impulse pressures produced during collapse of a vapor cavity result in severe damage of tubes.
Highlights
Modern hydraulic systems are widely applied to various industrial fields
A number of approaches have been introduced for the simulation of the pipeline transients including the method of characteristics (MOC), wave characteristics method (WCM), finite volume method (FVM) [25], finite element method (FEM), and finite difference method (FDM)
With the method of characteristics (MOC), the partial differential equations can be converted into ordinary differential equations
Summary
Modern hydraulic systems are widely applied to various industrial fields. Routinely, for pressure testing of segmental pigging, pigs are usually employed to remove liquids and deposits after the pressure testing. Pressure testing, which includes strength tests and tightness tests, is an important part of the guarantee for the safe operation of oil and gas pipelines. Air is accessible and inexpensive, it was utilized as a medium and the pressure is increased gradually to values that the pressure testing requires. Pigging process is safe under low pressure because after pressure testing, operation staffs will decrease pressure by discharging the water through the valves at the end of pipes. Due to varying elevation profiles, there are always some segments with a long slope, especially in a mountainous area and pigging operation, that should deal with new problems. For full-flow pipes with a long slope, valves opening and moving pigs may cause liquid transients in a pipeline. Pigging process is subject to rapid pressure transients, resulting in water-hammer events
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