Research On Four-point Bending Test Technology Of Large Diameter Pipeline

Along with the transformation of our energy structure to low carbon,oil and gas pipelines with large caliber and high steel grade have been built and used constantly.However,with the growth of service life,some of the pipelines have suffered from different degrees of problems such as damage or leakage,and in the actual operation of the pipeline,the environmental loads are complex and diverse,among which bending moment load plays a very important role in the strength and stability of the pipeline.The full-size pipe bending test can simulate the buried environment and operating conditions of the pipeline,accurately reflecting the force conditions during the service of the pipeline,so that the test results are true and reliable,but at present,the four-point bending test equipment and how to carry out the four-point bending test has not yet a relatively complete set of standards.In view of this situation,this paper studies the full-scale test technology of large diameter pipeline under the action of four-point bending,focusing on the design and analysis of full-size four-point bending test equipment and test methods of different pipe diameter,and provide test guidance for the study of bending behavior of full-size pipes under the action of four-point bending,the main research work and conclusions are as follows:(1)Developed a test system that can complete the complex load of internal pressure and bending moment of pipeline with the maximum diameter of 1422 mm,and designed and calculated the maximum thrust force and thrust range in the loading system of the test device.Then,carried out a full-scale four-point bending test on the self-made steel epoxy sleeve repairing pipeline with girth weld defects in the laboratory,and proposed the improvement of the four-point bending test method.(2)Through finite element calculated the effect of different loading indenter and support standoff dimensions on the bending performance of the pipeline,and the diameter of the loading indenter and support standoff should be consistent with the test pipe,and the radius is 1/2 circumference,and the width of the loading indenter can be 200 mm or 300 mm according to the length and diameter of pipeline.(3)Through the finite element simulation method simulated the bending deformation process of pipeline under the test pipe placement asymmetry,loading indenter position placement asymmetry,loading indenter vertical displacement loading asymmetry,different contact conditions between loading indenter with support standoff and pipeline,get that the four-point bending test should try to achieve symmetric loading and smooth process loading contact surface.(4)Carried out the pipeline in different span ratio,diameter-thickness ratio of the four-point bending simulation calculation,obtained the following conclusions: the inner span of the pipeline shall not be greater than 6D,and not less than 2D + 0.24m;the length of the pipeline should be at least 2.5 times the inner span.