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

Abstract

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.

Optimization of Hammer Peening Process for Gas Turbine Rotor Straightening

“…Ferreño et al [26] have demonstrated that the end results of the flaming of a steel beam can be predicted using finite element analysis. Chavoshi et al [27] have demonstrated that the end results of the hot spotting of a hollow shaft can be predicted using finite element analysis. Hu et al [28] have shown that the effect of laser peening on the geometry and residual stresses of specimens can be predicted.…”

Increasing bending angle in thick-walled pipes with wide heating

“…In our previous researches [1,8], the spot heating of a pipe was optimized using the Gaussian heat distribution of the torch to increase bending. The parametric study showed that increasing the heating zone radius and the maximum heat intensity, first, led to an increase in pipe bending angle and then a decrease.…”

“…The heated zone expands and is subjected to the pressure of the surrounding cold zone. Increasing the temperature leads to an increase in compressive stress and a reduction in the yield stress of the heated zone, a slight bulging, plastic strain, and ultimately reducing the length of the heated zone after cooling and deformation of the piece [1,2]. Li and Yao [3] examined various mechanisms of thin pipe deformation by heating.…”

“…In our previous studies [1,8] the pipe bending angle was increased by optimizing the hot spot parameters. CFD analysis of flame flow is carried out to determine the heat flux distribution over the pipe surface.…”