Analysis Method Of Dynamic Response Of Crack Pipeline

Submarine pipeline construction is one of the key projects of marine oil and gas engineering construction. However, crack and damages are inevitably occurred in submarine pipeline due to material aging and environment or human factor. In the area of seismic activity, there is huge potential risk of crack pipeline, so it is necessary to do the seismic research of crack pipeline. However, most of the existing research is based on complex finite element analysis method, the calculation efficiency of which is lower and can’t meet the requirement of rapid analysis of structure. A rapid calculation method is developed in this paper to simulate the dynamic response of free spanning submarine crack pipeline, and the related research is done.Dynamic analysis model of free spanning submarine crack pipeline is established based on the local flexibility theory. A program is written to calculate the seismic response of crack pipeline in MATLAB environment, and the seismic response schedule of crack pipeline is calculated through typical examples. At the same time the3-d finite element analysis method is used to simulate the seismic response of crack pipeline. By comparison, the two analysis results correlate well, which verifies the validity of this method. It shows that this method not only can accurately simulate the seismic response of the crack pipeline, but also greatly improves the calculation efficiency comparing with the traditional finite element software. This method can realize the quick structure analysis of the seismic response of crack pipeline and provide a kind of effective method for the seismic safety evaluation of crack pipeline.The formation of crack pipeline, and the seismic schedule charts of strain, shear, bending moment and displacement of crack element is calculated using the suggested method. The calculation results show that the crack causes minor changes on the pipeline formation, obvious influence on the strain of crack element, and little influence on shear, bending moment and displacement. The deeper the crack in the same position of the pipeline, the more obvious the convex near the crack position of the pipeline formation, and the larger the strain of the crack element. In the process of seismic response, the strain, bending moment and displacement of crack element of simply supported pipeline is much larger than that of crack element in the same position of clamp supported pipeline with the same parameters. So more damage and failure may occur in the simply supported crack pipeline than in the clamp supported crack pipeline.Stress of crack pipeline in alternating loads can be calculated rapidly using the suggested method. Stress schedule is cycle counted using rain flow counting method, and the stress amplitude and cycle times is got, then the stress intensity factor amplitude of the crack is calculated. According to the theory of fatigue life prediction, the fatigue life of crack pipelines in different conditions is estimated through typical examples. The results show that the stress of crack pipeline in alternating loads is far below the yield stress, but their fatigue life is very short.