The Effect Of Heat Source Characteristic On The Influence Of Local Heat Treatment On Columnar Components

Boilers, pressure vessels and pressure pipelines are three kinds of the special equipments that extensively used in industry production and people's life. Their main structure or major assemblies, most are cylindrical welding structures. In order to improve the welding joints'performance and eliminate residual stress, local heat treatment (LHT) is often taken out. At present, there are big differences still between Chinese and foreign standards about LHT. Some of these standards are lack of operability. And most researches about LHT were studied only with given temperature heat flux, but ignoring the influence of the heat sources'characteristic. So the popularization and application of these researches were limited.In this paper, finite element analysis (FEA) were used to study the LHT of the cylindrical structures. The viewpoint was proposed that the basic difference between the actual heat source(AHS) and the ideal heat source(HIS) were caused by the inhomogeneity during the output process of heat in time and space. APDL programes for analysis were programmed. The effects of layers of ceramic and thin layer of air simulated in the models on the characteristics of uniform and nonumiform heat source were explored. And the characteristics of uniform and nonuniform heat source were also researched by changing the number of resistance wires or layers of heating in the models. A lot of valuable conclusions were obtained.The existence of layers of ceramic and thin layer of air cause the cylinder's temperature changing is later than the resistance wires'.The concept of Uneven of Temperature Field(UTF) was raised. And the decrease of then number of resistance wires will lead to the increasing of UTF in the same condition of heating area and temperature raising speed.The concept of Maximum Relative Scale of Thermal Radiation(MRSTR) was raised as well. And the MRSTR gradually reduce with increasing the number of resistance wires. Furthermore, when there are more than 30 resistance wires in the model, the MRSTR tends to be a constant. It means that MRSTR will be no longer related to the number of resistance wires.The number and position of the resistance wires in nonuniform heat source will affect the LHT process evidently. All the curves of nonuniform heat source of temperature, heat flux, stress on the inside and outside of the cylinder exist fluctuations around the curve of the uniform heat source's, and all the peak value of the temperature, heat flux and stress appears at the position where the resistance wires were set. Increase the number of resistance wires can reduce the residual stress and peak value of the temperature and stress in the process of LHT, as well as the fluctuate range of temperature and stress, and is propitious to ameliorate the uneven of temperature and stress field. When the number of resistance wires is greater than 12, the effects of increasing the number of resistance wires on the greatest value of residual stress will be remarkably weakened, and the level of equivalent stress close to the level of the uniform heat source's. When the number of resistance wires is greater than 30, the effects of increasing the number of resistance wires on ameliorate the uneven of temperature and stress field in the LHT process will be remarkably weakened as well.