Water Treatment Operator-in-Training (OIT) Practice Test

Which part of a concrete pipe in a gravity sewer is most vulnerable to corrosion from septic wastewater?

1. Sole

2. Sides

3. Invert

4. Crown

The correct answer is: Crown

In a gravity sewer, the crown of a concrete pipe is most vulnerable to corrosion from septic wastewater due to its positioning and the way wastewater interacts with the surfaces of the pipe. The crown is the top part of the pipe where the flow of wastewater is less turbulent, which can lead to stagnant areas where corrosive elements from the wastewater can accumulate. Additionally, septic wastewater often contains various corrosive substances, including sulfides that can produce hydrogen sulfide gas. This gas can rise and accumulate at the crown, leading to accelerated corrosion. Over time, this can cause significant deterioration in the concrete, potentially compromising the structural integrity of the sewer system. The sole, sides, and invert of the pipe are typically less exposed to these corrosive effects because they are more likely to remain submerged in the wastewater flow, where the circulation helps to disperse harmful substances. Understanding the specific vulnerabilities of each part of the pipe is crucial for effective maintenance and rehabilitation of sewage infrastructure.