Impact of Mining Subsidence on Natural Gas Pipeline Failures

Abstract

The main goal of the paper is to present the influence of ground deformations, caused by mining subsidence, on natural gas pipelines. There are also presented characteristic examples of the gas pipelines failures in mining areas in Poland. Failures of buried natural gas pipelines pose a threat to people and the environment due to gas leaks. The main reasons of the leaks are corrosion of steel pipelines, mechanical damage as a result of construction works and unsealing of joints as well as expansion joints. In mining areas, the gas pipelines are influenced by ground deformations. Mining extraction induces subsidence, horizontal displacements, horizontal strains and curvatures of the subsurface ground layer where natural gas pipelines are buried. The horizontal strains are of significant importance for the considered issue. The mining-induced ground deformations cause displacements of pipelines as well as additional longitudinal tensile and compression loads. The load values depend on the soil-pipe friction coefficient, pipeline depth and pipeline section length subjected to horizontal strains. The load conditions also change in the transverse direction of pipelines. In Polish mining areas distribution gas pipelines are constructed with steel and polyethylene pipes. Transmission gas pipelines are constructed with steel pipes. The steel gas pipelines usually are equipped with built-in expansion joints to protect them and to transmit ground deformations. The polyethylene gas pipelines are flexible and are able to transmit mining ground deformations but polyethylene pipes can be used up to 1,0 MPa nominal pressure in natural gas systems. Mining extraction causes additional failures of the gas pipelines despite their above mentioned capacities. The failures occur most frequently in the steel gas pipelines, particularly in old ones. The main causes of gas leaks are wall breaks, mostly near welded areas, wall buckling and sealant damage of expansion joints. Mining deformations can also induce the buckling of polyethylene pipelines. Therefore, in mining areas additional inspections of the natural gas network are needed to detect the leaks early.