Applicability of Medium Density Polyethylene Gas Pipes in Hot Climate Areas of South-west Iran

The applicability of medium density polyethylene (MDPE) gas pipes in hot climate areas of southern Iran (such as Khuzestan) has been one of the main concerns of local gas company officials and their engineers. This is due to the facts that buried pipes can experience sever stresses due to internal pressures, traffic load, soil height, daily and/or seasonal temperature variations if not properly designed and installed underground. This research investigates the sole effect of each parameter and their combination on maximum stress produced in MDPE gas pipes and their sockets which are made from PE100. The analysis was performed through a comprehensive finite element process and the results were compared to those of empirical equations, where possible. The maximum local stresses in pipes and sockets were determined and compared to their critical values for an operating pressure of 4 bars at various depths and temperatures. The design curves and the range of applicability of MDPE are then deduced based on a life time of 50 years. According to the results, assuming a target temperature of 30ºC for the pipe and its socket, then MDPE pipe and its HDPE socket (PE100) can well sustain the imposed load of a temperature rise of 15ºC at a depth of 120 cm, in presence of all other loads mentioned above. For higher temperature rises, some stress relief mechanisms must be employed. Hence, by applying the right procedure, these pipes can be used for gas transportation even in hot climate areas of Iran, where the ground surface temperature may reach a high value of 67ºC in summer time.