A Review on Seismic Design Criteria for Pipelines, Emphasized on Buried Gas Pipelines

In this paper, seismic design criteria of pipelines, especially for buried gas pipelines from different codes, guidelines and researches are reviewed and compared. For buried or above ground pipelines, both seismic wave propagation, sometimes called as transient ground deformation or TGD, and permanent ground deformation or PGD are important, but for above ground pipelines, like other above ground structures, seismic wave propagation is more critical than PGD, and usually is represented by earthquake induced acceleration, or PGA. Adversely, for buried pipelines, seismic wave propagation has less destructive effects on pipelines than permanent ground deformations, such as faulting, settlement, liquefaction induced lateral spreading, and landslide. Generally, combinations of both seismic effects are applied to pipeline, with different magnitudes and importance. Also, in most cases, wave propagation affects a larger area with small intensities, while PGDs have more devastating effects in limited locations. Gas pipelines are considered as an important part of lifelines, due to vast industrial and urban usage of gas and its increasing demand, as a clean and yet, cheap source of energy. Pipelined design is mainly based on mechanical and processing needs, where pipe size and thickness are determined. For highly seismic areas, structural design considering earthquake induced loads is also important. A very useful way to indicate wave propagation effects in pipelines, is Newmark’s theory, in which he relates pipeline axial strain caused by TGD effects, to the pick ground velocity, PGV, and apparent wave propagation velocity. After Newmark, different researchers have modified this relationship to account for different types of seismic waves, soil properties, pipe geometry and importance, and it has been mentioned in different codes and guidelines, such as ALA 2001, Eurocode 8, and ISDCOI-038. After calculation of axial strain, it shall be compared with allowable strain, which depends on pipeline material, and type of strain (tension or compression). Permanent ground deformations are other destructive seismic effects, and include different types, such as faulting, landslide, liquefaction induced lateral spreading, and settlement, for two former cases, codes such as IITK GSDMA have proposed some relationships. For landslide, direction of soil movement with regard to pipeline direction will cause axial, bending or combined forces in pipeline, which in turn initiates axial strains in pipeline section and shall be compared with allowable strains, as mentioned before. When faulting occurs, if fault trace crosses the pipeline, some deformations will happen in pipeline, which shall be calculated based in faulting mechanism, angle of crossing, soil properties, event magnitude, and pipeline importance, and subsequent strains shall be compared to allowable strains. To determine amount of ground deformations caused by faulting, various relationships are available, between which, those proposed by “Wells & Coppersmith” are more common. In these formula, pipeline deformation caused by faulting will be determined, multiplied by pipeline importance factors, and subsequent strains shall be compared with allowable strains. For aboveground pipelines, pipeline span or distance between supports is important and addressed in many technical documents and regulations. In some cases, such as trance Alaska oil pipeline, usage of flexible supports able to move horizontally in direction perpendicular to pipeline direction, has led to less seismic vulnerability in reported seismic events.