Vulnerability Assessment of Buried Pipelines

Abstract

Pipelines have been acknowledged as the most reliable, economic and efficient means for the transportation of water and other commercial fluids such as oil and gas. They are often referred to as “lifelines”, since they carry materials essential to the support of life and maintenance of property. The earthquake safety of buried pipelines has attracted a great deal of attention in recent years. Many buried pipelines in India run through high seismic areas and therefore are exposed to considerable seismic risk. Pipelines running through high seismic zones should be designed in such a way that they remain functional even after subjected to high intensity earthquake shaking. In this report, performance of one of the high pressure gas pipeline in the state of Gujarat, under the fault movement and soil liquefaction is carried out. Based on the result from the study some recommendations are made to minimize the effect of earthquake on the existing pipeline. In the design of a pipeline for crossing a fault line, the following considerations generally will improve the capability of the pipeline to withstand differential movement. The following recommendations are as follows: 1. The pipelines crossing fault line should be oriented in such a way to avoid compression in the pipeline. Abrupt changes in wall thickness should be avoided within fault zone. In all areas of potential ground rupture, pipelines should be laid in relatively straight section avoiding sharp changes in direction and elevation. 2. To the extent possible, pipelines should be constructed without field bends, elbows, and flanges that tend to anchor the pipeline to the ground. If longer length of pipeline is available to conform to fault movement, level of strain gets reduced. Hence, the points of anchorage should be provided away from the fault zone to the extent possible in order to lower the level of strain in the pipeline. 3. The burial depth of pipeline should be minimized within fault zones in order to reduce soil restrain on the pipeline during fault movement. Pipelines may be placed on the above ground sliding supports. 4. In the design of a pipeline for in the Liquefied zone, the following considerations generally will improve the capability of the pipeline to withstand buoyancy force due to soil liquefaction. The buoyancy effect can also be minimized by shallow burial of the pipeline above the ground water level. An increase in pipe wall thickness will increase the pipeline’s capacity for buoyancy force due to soil liquefaction.