Efficiency of controlling crystallization front movement in welding polyethylene pipes under low-temperature conditions

Аuthors

Starostin . P., Ammosova O. A.^*

Institute of Oil and Gas Problems SO RAN,

*e-mail: ammosova_o@mail.ru

Abstract

Nonlinear inverse heat conduction problems are employed to facilitate the welding of po-lyethylene pipes at ambient temperatures that fall below the levels recommended by regulatory stan-dards. The proposed technique for low-temperature welding consists of several operations: preliminary heating, temperature equalization, heating according to a specific welding mode at permissible air temperatures, and cooling with controlled crystallization of the welded joint material. All these operations are performed automatically. To determine the parameters for heating and temperature equalization – such as heater power, heating duration, and equalization temperature – direct heat conduction problems are solved. Regression equations are utilized to establish these parameters based on the ambient temperature and the diameter of the pipe in the welding machine. The functions controlling the motion of the crystallization front in the developed prototype for welding polyethylene pipes of various diameters in naturally low temperatures are determined by solving inverse heat conduction problems, combined with a full factorial experiment methodology. The influence of the distance from the heater to the temperature setting points on the solution of the inverse problem has been analyzed. Calculations have identified the optimal distance for temperature information setting points from the heater, ensuring that the solution minimizes the quality functional and maintains temperature dynamics within an acceptable range of variation in the heat-affected zone. Thermal analysis has shown that the curves representing the rates of change in the degree of crystallinity for joints created by standard welding and those utili-zing crystallization control are closely aligned. This indicates the formation of similar supramolecular structures. Physicomechanical testing has demonstrated that implementing crystallization control guarantees the strength of welded joints made at low temperatures, equal to or exceeding that of joints welded under standard conditions. The results of strength tests confirm the effectiveness of the crystallization front control method when welding at low temperatures. The proposed method for establishing welding modes at low temperatures in a welding machine, which involves solving direct and inverse heat conduction problems, can be recommended for determining the parameters and functions required for welding polyethylene pipes and other components with built-in heaters in low air temperature conditions.

Keywords:

thermal process, welding, polyethylene, embedded heater, crystallization, inverse problem, heat-affected zone, differential scanning calorimetry, strength

References

1. Starostin NP, Ammosova OA. Crystallization front movement control when welding polyethylene pipes at low temperatures. Thermal Processes in Engineering. 2024;16(4):162–169. (In Russ.).

2. Starostin NP, Ammosova OA, Petrov DD et al. Welding of polyethylene pipes by couplings with embedded heaters at low temperatures. Part 1. Realization of crystallization front control. Wel-ding and Diagnostics. 2024;(6):44–49. DOI: 10.52177/2071-5234_2024_06_44 (In Russ.).

3. Starostin NP, Ammosova OA. Simulation of preheating and heating when connecting polyethy-lene pipes with electrofusion couplings. Petroleum Engineering. 2024;22(5):149–158. DOI: 10.1712 2/ngdelo-2024-5-149-158 (In Russ.).

4. Alifanov OM. Identification of heat transfer processes in aircraft. Moscow: Mashinostroenie; 1979. 216 p. (In Russ.).

5. Bubnov VA, Solov'ev IA. On the use of hyperbolic equations in the theory of thermal conductivity. Engineering and Physics Journal. 1977; 33(6):1131–1135. (In Russ.).

6. Samarskii AA. The theory of diference schemes. New York, Basel: Marcel Dekker Inc; 2001. 761 p. (In Russ.).

7. Adler YuP, Markova EV, Granovskii YuV. Experiment planning in the search for optimal conditions. Moscow: Nauka Publ.; 1976. 279 p. (In Russ.).

8. Khartman K. Planning an experiment in the study of technological processes. Moscow: Mir Publ.; 1997. 278 p. (In Russ.).

9. Godovskii YuK. Thermophysical methods of poly-mer research. Moscow: Khimiya Publ.; 1976. 216 p. (In Russ.).

10. Petrov DD, Botvin GV, Starostin NP et al. Method of testing the coupling welded joint of polymer pipes. Patent RU 2802888, 05.09.2023 (In Russ.).