Metal pipes often fail due to which of the following?

Metal pipes frequently experience failure due to galvanic action, which occurs when two different types of metals come into contact with each other in the presence of an electrolyte (often water). This creates an electrochemical reaction that leads to corrosion of the more anodic metal, gradually deteriorating the integrity of the pipe. As corrosion eats away at the metal, it can lead to leaks and ultimately pipe failure.

In the context of wastewater collection, understanding galvanic action is vital for maintaining the longevity and performance of metal piping systems. Preventive measures, such as the use of insulation between different metal pipes or utilizing sacrificial anodes, can help mitigate the effects of this phenomenon.

Other options mentioned, like back siphonage, browning movement, and reverse osmosis, do not specifically relate to the direct corrosion of metal pipes in the same manner as galvanic action. Back siphonage refers to the backflow of contaminated water into clean water supplies, while browning movement and reverse osmosis pertain to different processes involving water treatment and filtration rather than corrosion of metal materials. Thus, galvanic action is the primary concern for metal pipe failure in wastewater systems.