Structural and fractographic features of fracture of the heating system collector under the influence of groundwater

The causes of premature failure (after 10 years of operation) of an underground collector in a poultry farm heat supply system were analyzed. It was found that the combined effects of groundwater, the use of low-quality steel, and the lack of corrosion protection during the collector installation caused the decrease in its service life. A system of nearly parallel intergranular cracks extending from the outer surface was detected in the axial cross-section of the collector wall made of steel 20. Dense layers of corrosion products filled the spaces between the crack edges, with their larger volume relative to unoxidized metal creating additional pressure on the crack edges, increasing the stress-strain state at their tips and facilitating their deeper propagation into the collector wall. The ferrite-pearlite structure of the steel, with its distinct texture and non-metallic inclusions along the grain boundaries, facilitated crack propagation both across and along the striated structure. Under the pressure of corrosion products at the edges of these longitudinal cracks, the outer layers of metal were sequentially separated from the collector surface, reducing its wall thickness and localizing the damage process in the thinnest cross-section. Fractogra­phic analysis confirmed this sequence of damage initiation and propagation from the col­lector outer surface. It was concluded that, despite the steel satisfactory mechanical properties, the collector failed prematurely due to structurally determined weakening of grain bounda­ries and the free access of groundwater to the metal.