Increasing bending angle in thick-walled pipes with wide heating

The spot heating of a metal part leads to many small deformations. The applications of this method are straightening the bridge parts, turbo-machinery shafts, and so forth. The movement of the heat source on a given path (line heating) leads to an increase in the deformation and the possibility of creating complex bends. However, it is complicated to predict and control the path and velocity of the heat source as well as determining the heat intensity. In the pipes, this method requires simultaneous control over the two torches on both sides of the pipe. The present study aims at investigating the mechanism of deformation and increasing the bending angle in thick pipes by means of a simple heating method. At first, the maximum bending in heating a large circular zone (entitled “wide heating”) is obtained by simulating the process using finite element method and optimizing it applying the genetic aggregation algorithm. Then, a new method for simultaneous heating within two zones is introduced. The interaction between two zones leads to the development of the shortening mechanism in the pipe wall and a significant increase in the bending angle. In this method, there is no need to move the torch where the temperature is controlled more accurately. To evaluate the finite element model, several pipe heating tests are performed with their results being agreed well with the simulation results

Bending improvement in Spot Heating of pipes in comparison with Line Heating method

In Spot Heating, a small area of a metal part surface is heated quickly with a gas torch, laser beam, or induction coil to a temperature below the phase change temperature and then cools down. The heated area undergoes compressive plastic strain and the part gets deformed. This method is usually applied as trial and error for straightening shafts, bridge components, ship structures, etc. The conventional straightening mechanism in industries involves creating thermal gradient mechanism (TGM) and shortening. Many studies have been conducted for bending of thin pipes (at a maximum thickness of 2 mm) with the induction of “shortening” by laser. Spot Heating, despite its simplicity, results in very small deformations. The present study aims to increase the deformation in the Spot Heating method so as to extend its use in pipe straightening. To meet this goal, the shortening mechanism is developed through a thick pipe wall by optimizing the heating parameters. CFD analysis of flame flow is carried out to determine the heat flux distribution over the pipe surface. Also, the finite element method and optimization are used to analyze and raise the pipe deformation mechanism. The results indicate a considerable increase in the pipe bending which reduces the stages necessary for the pipe straightening in industries. Furthermore, the appropriate distance for combining the hot spots is also obtained. To evaluate the results, the Spot Heating test is performed, showing appropriate agreement with the simulation results