Mechanics Study On The Failure Mechanism Of The Buried Polyethylene Gas Pipelines

Because of polyethylene (PE) gas pipelines's excellent properties, they gradually replace the steel pipelines and are wildly used for underground gas pipeline network. Failure of PE gas pipelines may result in Major Hazard Accident. So failure analysis and mechanics study on PE gas pipelines in Service has great importance to prevent from the possibility of accidents takes place. People at home and abroad usually use analytical method to calculate the stresses in the buried polyethylene gas pipeline. This method doesn't consider creep behavior of PE pipe and pipe-soil interaction. Results of analysis are inaccurate. On the other hand, the conventional experiment of PE pipe can't be spread and applied because of its strict experimental condition. This paper form mechanics analysis method combined with engineering practice center around the ductile failure and brittle failure of PE pipe. This method considered not only imperfection of pipeline and traffic load but also mechanical property of pipe material is viscoelasticity. So the analysis results will approach the real situation. This paper designed a simple experimental method for determination of mechanical properties of PE pipe. This method can be use in quality evaluation and long-term performance prediction of PE pipe. The main results are summarized as follows:(1) Determination of mechanical properties of PE pipe. This paper designed and practiced the constant lateral pressure experimental method for determination of creep property of PE pipe base on viscoelastic theory. On the other hand, the yield stress and elongation at break of PE pipeline are determined by tensile experiment. The experimental results can reflect strength and toughness of PE pipe. Both of the experiments can be use in quality evaluation.(2) Establishment of the mechanical model of PE pipe. According to the relaxation module curve, the viscoelastic mechanical model of pipe is built by viscoelastic theory. The general computation program (ANSYS) is utilized to make finite element analysis on the constant lateral pressure experimental. Compared with the two groups of data, the mechanical model is verified.(3) Mechanics study on the buried polyethylene gas pipelines. The FEM model of buried polyethylene gas pipeline was established in use of the viscoelastic mechanical models we find out. Apply traffic load and do transient analysis. The changing relation curves of pipe stress and the deformation in pipe diameter along with time were obtained. With differences of pipeline laying depth, the mechanical behaviors of underground pipelines were compared. Mechanics study on the simulation experiment of the buried polyethylene pipelines to verify the mechanics analysis method. It is observed that viscoelasticity of polyethylene decrease pipe stress gradient. And covering soil has effect on load reduction under the traffic load.