Study On Over-bending Setting Round Process For Pipe-edn Of Large Pipes And Intelligent Control Technology

Large steel pipes are one of the indispensable parts in the construction ofinfrastructure. The relative research indicates that100％global gas and85%globalpetroleum rely steel pipeline transportation, there is also a considerable number of largesteel pipes in the nuclear power and thermoelectric facilities and municipal supplynetworks. In recent years, along with China’s infrastructure construction progresses, theneeded large pipes production is gradually increasing. However, the sharp rise of the pipesmakes increasingly brutal competition between manufacturers, thus to allowmanufacturers to put forward new requirements for the quality of the pipes.Ovality of pipe is one of the main standard to measure the quality of the pipes. And ifthe ovality of the pipe-end is out of standard, it will directly affect the connection processbetween pipes. In the production process of the pipes, it is unavoidable to produce somepipe with ovality oversize because of the fluctuations of the material properties and manybad factors in production process. So the setting round process is needed. According towhether perimeter changes of the pipe section neutral layer, the setting round process canbe divided into “sizing and setting round” and “over-bending settiong round”. However,the latter is widely applied by the manufacturers although technological backwardness.Thus, the advanced methods are veritably needed.Firstly, under the range of engineering applications accuracy, and to simplify thetheoretical analysis difficulty of the over-bending setting round, this paper proofsequivalence principle of curved beam pure bending, which means the pure bendingprocess of curved beam is equivalent to the addition of pure bending results of straightlybeam and the initial curvature of curved beam, and equivalence principle of over-bendingsetting round, which means the setting round process is equivalent to compressing ovalprocess.Secondly, according to conventional bending theory and finite element meshing idea,the theoretical analysis for the compressing oval process of the whole pipe is finished, andthe relationship between the ovality after springback and the relative reduction is built. This lay the theoretical foundation for the over-bending setting round.Thirdly, when the materials and the specifications are the same, the similarity relationbetween the pipe-end compressing oval process and the whole pipe compressing ovalprocess is given by experiment. Based on this, the “two steps” and “three steps”over-bending setting round control policy are built. Which means to obtain thespring-back law of the compressing oval process firstly by compressing the first pipetwice or three times, and then to set round the next pipe by the spring-back law, at last tomodify the spring-back law according to the setting round results. This lay the foundationfor the over-banding setting round intelligent control system.Fourthly, for the purpose of changing the situation that the ovality measuring workare finished by handwork, according to the characteristic of CCD machine cognition, thepipe-end ovality recognition system is developed in the VC++program language. Thesystem researches into primary algorithms, such as the pipe-end image pre-processing, theoval recognition based least square method, the triangle foul line recognition and so on,and put forward a new camera calibration method. The final experiment proves thereliability of the system.At last, base on the control policy and the pipe-end ovality recognition system, theover-bending setting round intelligent control system for pipe-end of large pipes is built.The system is proved to be good stability, high degree of automation and reaching idealeffect.