N. P. Starostin, M. A. Vasilieva
SUBSTANTIATION OF TECHNOLOGICAL OPERATIONS OF WELDING A SADDLE BRANCH TO POLYETHYLENE PIPES AT TEMPERATURES BELOW AVAILABLE
Additional branches for gas supply systems are generally installed during the completion
of the construction of a gas pipeline, often falling in the autumn or winter time, when the air temperature is below the maximum allowable for welding polyethylene pipes. At ambient temperatures below minus 15 °С, it is recommended to weld polyethylene pipes under a shelter, where the temperature is maintained in the permissible temperature range.
The paper proposes a mathematical model for the thermal process of welding a saddle branch to a polyethylene pipe taking into account the heat of phase transition. The corresponding three-dimensional non-linear heat equation is solved by the finite element method. As an example, calculations were made for a PE 100 SDR 11 polyethylene pipe and a 100/63 saddle tap. Comparison of the calculated and experimental temperature data establishes the adequacy of the proposed mathematical model to the actual thermal process of welding a saddle branch to a polyethylene pipe.To obtain a high-quality welded joint, it is necessary to ensure that the temperature field changes according to a certain regularity in the heat-affected zone. Admissible regularity is ensured when welding is performed in the range of climatic air temperatures of above minus 15 °C. In this study, examples are considered for the definition of simple technological operations that ensure such regularity at ambient temperatures below normative ones. For comparison, the dynamics of temperature fields at ambient temperatures of 20 °C and minus 40 °C was calculated. Technological operations necessary to weld a saddle branch at the temperatures below the standard are determined from studying the dynamics of temperature profile during the welding of the saddle branch to a polyethylene pipe at various ambient temperatures.
Keywords: mathematical model, finite element method, temperature, calculation, thermal process, welding, phase change, crystallization
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