Research On The Ultimate Load Carrying Capacity Of Steel Pipes With Ring Weld Defects

Pipeline as the most common way of oil and gas transportation,usually need to use welding methods to connect multiple pipe sections into a complete whole,in the welding seam there are usually some inevitable welding defects,and the defective parts are also the weakest part of the pipe,the most prone to damage.And the pipeline in the process of oil and gas transportation,in addition to the internal transport medium for the pipeline pressure load,mainly by the external environment is the role of bending load,and for the large diameter of thin-walled pipeline,bending load caused by the elliptical deformation of the bearing capacity of the pipeline has a greater impact,but the current domestic research on the elliptical deformation of the ultimate bearing capacity of the defective pipeline is relatively small However,there are relatively few studies on the ultimate bearing capacity of defective pipes after elliptical deformation.This paper mainly focuses on the plastic ultimate load calculation of thin-walled pipes with unwelded defects of large pipe diameters under combined load conditions,the calculation model of pipes with unwelded defects and the establishment of safety assessment curves,and the main research results achieved in this paper are as follows:(1)Considering the elliptical deformation of the pipe cross-section when the pipe is subjected to moment load,the existing formula for calculating the plastic ultimate load of a pipe containing a single unwelded defect under the combined action of internal pressure and moment load is improved and established,and the correctness of the obtained formula is verified by using the results of the scholars’ tests,and the procedure for solving the ultimate moment load capacity of the pipe is written using Math CAD according to the obtained theoretical formula.(2)Combined with the team in the experimental process,the actual test pipe nondestructive testing,the class of ring defects such as unweld defects to simplify;at the same time combined with the actual test conditions,the establishment of numerical calculation model containing unweld defects pipe,and using the results obtained from the theoretical calculation of the plastic ultimate load equation of the pipe containing a single ring weld defects to further verify the correctness of the established numerical simulation model,and then study the influence of the size parameters of unweld defects on the ultimate load.(3)The influence of each size of the ring weld defect on the safe bearing performance of the pipe under different loading conditions is obtained through the numerical model of several pipes containing different sizes of unwelded defects under different loading conditions.At the same time,the safety assessment curves for pipes with single ring weld defects are obtained through several finite element calculations and the corresponding equations are fitted,and finally the safety assessment method for pipes with single ring weld defects is obtained.