Research On The Plastic Limit Load Solution Of Pressure Pipe With Incomplete Penetration Flaw

Industrial pressure pipe is absolutely necessary key special equipment for national important project construction, and incomplete penetration flaw is the most common weld flaw in pipeline, which decreases the limit load-carrying capacity and constitutes the great threat toward the safe operation of pipe. So the research on the load-carrying capacity and safety assessment method for pipe with incomplete penetration has extremely important theoretical and realistic significance.According to the actual loading-bearing condition of industrial pressure pipe, this paper studied the limit load-carrying capacity of pipe with incomplete penetration flaw. The main research contents and results are as follows:(1) Based on the extended Net Section Collapse (NSC) criteria, the plastic limit load analysis method for pipe with single incomplete penetration flaw under combined internal pressure and asymmetrical bending moment was supplemented and perfected, and presents an analytical method for plastic limit load of pipe with two inner surface circumferential flaws under combined internal pressure and bending moment. Then the influence of several parameters such as flaw sizes were analyzed and the conservation of flaw combination was studied, it indicates that the proposed method for predicting plastic limit load of pipe with two flaws can effectively reduce the conservation, so it is appropriate to use in fitness-for-service assessment method.(2) An experimental platform used for testing the plastic limit load of pressure pipe under combined loadings was established and experimental research on the limit load-carrying capacity of flawed pipe under pure internal pressure, pure bending moment or combined internal pressure and bending moment was proceed. By comparing the experimental results with Finite Element Analysis (FEA) results and analytical method, it shows that the Finite element analysis and analytical method for plastic limit load are reliable.(3) Based on systematic finite element analysis, the failure mode of the mismatch welded pipe with incomplete penetration flaw was analyzed and the mismatch limit load for pipe with flaw was presented, which offers significant benefit in assessment of mismatch welded pipe with flaw.(4) The plastic limit load solutions for thick-wall pipe with incomplete penetration flaw was proposed under the assumption of uniform stress distribution. The comparison with FEA results indicated that the proposed plastic limit load solutions for thick-wall pipe can get an accurate or conservative solution.