The highly insidious and persistent corrosion of sewage pipes caused by hydrogen sulfide

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The corrosion of sewage pipes by hydrogen sulfide is a multi-dimensional, gradual destructive process with a complex mechanism of action; it causes damage to the pipes in a subtle and persistent manner. From the perspective of chemical corrosion, when hydrogen sulfide gas comes into contact with water on the inner surface of pipes, it dissolves to form hydrosulfuric acid. Hydrogen sulfide is acidic and can undergo chemical reactions with the material of pipes. In the case of commonly used reinforced concrete pipes, hydrosulfuric acid reacts with alkaline substances in the concrete such as calcium hydroxide (Ca(OH)₂), producing compounds like calcium sulfate (CaSO4). This reaction continuously consumes the alkaline components in the concrete, damaging its structural integrity; as a result, the concrete surface becomes porous and peels away, exposing the rebar inside. When pipe corrosion reaches a certain degree, its structural strength drops sharply, and it can no longer withstand the pressure from the soil, roads, and vehicles above it, making pipe rupture and collapse likely to occur. After a pipeline collapses, a cavity is formed underground. Over time, the soil surrounding it gradually flows into the cavity, causing the ground to sink. At first, settlement may be only slight, manifesting as tiny cracks or minor depressions in the road surface, which do not easily draw the attention of pedestrians and vehicle drivers. However, as soil erosion increases, the extent of the underground voids will gradually expand, and road surface settlement will become more and more apparent. When the cavity expands to a certain extent and can no longer support the weight of the road above it, severe road collapse accidents occur.