Study On Section Stability Of Large Diameter And High Grade Steel Buried Pipeline

As the long-distance oil and gas pipelines tend to develop towards the direction of high pressure and large diameter, the requirement of steel grade improves. Nowadays, high-grade steel pipelines with large diameter are widely used, such as X80steel pipelines. However, as the steel grade improves, the diameter increases, the wall thickness decreases, the stability of pipelines deserves more and more attention. Except the pressure from the overlying soil, buried pipelines will also be effected by other static loads and impact loads, some of the loads even give rise to the stability failure of the pipe cross section. Hence, it is practical significance to research the stabilization of high-grade steel pipelines with large diameter.The paper mainly studies the stability failure law of buried X80pipelines with1219diameter under the condition of vertical loads and analyzes the deformation of pipelines in detail. The basic theories of stability failure of pipelines are discussed and the main instability factor of pipelines section is also studied. Then compared and contrasted the deformation control criteria in domestic and foreign specifications and deformation characteristics of buried pipelines. Paper reasonably determined stability standart of pipeline section in the light of GB50253-2003.X80tubing of West-East gas and Hijo pipeline has been evaluated by statisticaly analysing the Mechanical parameters.For the X80buried pipelines which are intact or have ovalization deformation, finite element models are established under both the static load and the shock load by using ANSYS Software. And regularities of variation of stress and deformation along with main parameters are studied and analyzed. Models of pure round and elliptical buried pipelines under the static load are established and distribution rules of stress and deformation in the pipelines are found. The influences of main parameters like aspect ratio, depth, static load on the deformation (horizontal, vertical) are studied. Models of pure round and elliptical buried pipelines under the shock load are established considering the spread of the impact load in the soil. The influences of main parameters like aspect ratio, depth, dual shock loads, static load and the outside diameter deviation on the deformation (horizontal, vertical) and the computation are studied. Some practical suggestions of the buckling law of high-grade, large diameter steel buried pipelines are put forward by finite element analysis.The paper aimed at X80pipelines with typical diameter-thickness ratio (20,40,50,66.25,90,120,140,160). The horizontal deformation of the midpoint for both pure circle and elliptic buried pipelines under the extreme condition is analyzed by the stability standart of pipeline section. The diameter-thickness ratio of X80pipelines has been discussed with considering the influences of deviation grade between D1, D2, D3, D4.In this paper, the main research results are as follows:Deflection in the horizontal direction is an important index to determine how the pipelines section is destabilizing. The deflection in the horizontal direction is more relative to the vertical direction in conditions of the normal load model. The deformation velocity in the horizontal direction is more quickly relative to the vertical direction in conditions of the shock load model. According to the the ratio of deflection in horizontal direction to diameter (Δx/D) in conditions of the extreme load model, diameter-thickness ratio of X80pipelines (1219mm) which no-considering deviation grade is90and diameter-thickness ratio of X80pipelines (1219mm) which considering deviation grade from D1to D4is20,35,45,57respectively. The main research results provide reference for designing diameter-thickness ratio of the buried pipelines with large diameter and high grade steel.