Estimated Determination of Heat-Affected Zones for Welding of Polyethylene Pipes at Low Temperatures

摘要

The boundaries of heat-affected zones (HAZ) are determined by mathematical modeling of the thermal process of butt welding of polyethylene pipes for gas pipelines. When choosing the process conditions for welding of polyethylene pipes, as well as when investigating the quality of the welded joint, determination of the boundary of the heat-affected zone is of great importance, since structural changes of the welded materials occur in this zone. The mathematical model used takes into account the heat of the phase transition in the temperature range, as well as the thermal effect of burr formed during upsetting. The adequacy of the proposed mathematical model is shown by comparing the experimental and calculated temperature data. The temperature was recorded using a multichannel temperature programmer with a Thermodat-17E3 graphical display. The problem was solved numerically by the finite difference method. The developed algorithms are implemented as a set of programs in the Delphi environment. Numerical simulation was carried out for a 63×5.8 PE 100 GAZ SDR11 pipe. The admissible area of heat-affected zones is defined. It is formed at admissible air temperatures. The computational experiments have shown the possibility of controlling the temperature regime for welding under conditions of low ambient temperatures and providing the same temperature field variation in the HAZ as at permissible air temperatures. The time of its formation is fixed. By preheating the ends of a welded pipe and using a thermal enclosure weld during cooling at low temperatures, the desired location of the HAZ boundary is achieved.