Failure analysis of low carbon steel pipeline for district heating and cooling systems: Case studies

In this study, we investigated the failure modes of three low carbon steel pipelines used in district heating and cooling systems. Unlike thermal fatigue and external damage, which are typical causes of pipe failure in district heating and cooling systems, we observed unusual failure cases attributed to corrosion. Microscopic analysis, potentiodynamic polarization tests, and zero resistance ammeter measurements were conducted to analyze the root cause of failure. For the pipe elbow, stress analysis was performed using the finite element method. In the district heating system, fibrous inhomogeneous inclusions accelerated corrosion penetration in the pipeline. For the case of entrapped fibrous ceramic inclusions in pipe (350A), pore clusters formed by the inclusions acted as pathways for corrosion penetration. For the case of entrapped fibrous carbon inclusions in pipe (450A), corrosion penetration of pipeline due to galvanic effects occurred. In the district cooling system, bulging and plastic fracture were observed at the pipe elbow (250A), attributed to the freezing pressure exerted by water on the locally corroded weld joint.