Here are the main techniques used in city sewer inspections:
Visual Inspections
Inspectors physically enter pipes to inspect them with a flashlight.
Visual inspections can also refer to inspectors looking at the conditions surrounding a pipe or other components in wastewater infrastructure.
CCTV (Closed Circuit Television) Inspections
CCTV is commonly used for narrower pipes (4-48 inches in diameter), which are too small for an inspector to enter.
In a larger sewer system, a remotely controlled CCTV camera and its accompanying lights are attached to a raft, which is then floated between manholes inside a pipe while the camera is swiveled in the vertical and horizontal planes for full visual coverage of the pipe. In smaller sewers, the camera and lights can be attached to a sled.
The output of CCTV camera is a video recording with visual data on the condition within the pipe. Once the visual data is collected inspectors can review it to conduct a thorough visual inspection of the pipe and draw conclusions about possible maintenance needs.
Higher-end CCTV cameras offer these features to support sewer inspections:
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Automatic and remote (manual) focus
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Manual zoom up to 40x (optical and digital)
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Iris control
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Directional lighting capabilities for pipes anywhere from 6” to 48” in diameter
Camera Inspections
Camera inspections can also be done using a similar approach as that taken with a CCTV camera, where a camera is placed on a raft or sled and floated along within the pipe.
Lamping Inspections
A lamping inspection refers to a sewer inspection in which a camera is lowered into a maintenance hole and positioned at the center of the meeting place between the sewer line and the manhole opening.
Using this positioning, inspectors can collect visual data on the inside of the pipe and then review that data later.
Lamping inspections produce the lowest quality of visual data, and thus are only used on low priority pipes (this usually means newer pipes, which are less than 20 years old), or in projects where funds are extremely limited.
