Crawler Inspection of Dry Penstocks

A hydroelectric dam in the northeast United States had a planned dewatering for engineering inspection surrounding FERC relicensing and because of the steep angle of the penstocks, the engineering firm decided it would not be in the best interest of safety to perform walking inspections of these penstocks. Instead, they turned to Hibbard Inshore to conduct this interior inspection of the three penstocks using a crawling ROV with a color zoom tilt and rotate camera.

The vehicle needed to be small enough to pass through a 12”x 16” access door at the base of the surge shaft and capable of traveling up to 725’ down each penstock at a 45 degree downslope. The vehicle camera was used to follow each riveted joint to look for anomalies and also look for features of interest in each penstock section. Several features that were not on the as-built drawings were located, identified and recorded so that they could be assessed by the client’s engineering team. This inspection was able to get the customer the data they needed while allowing them to avoid a complex and possibly unsafe confined entry scenario.

In addition to the crawling inspection of each of the penstocks, the client asked Hibbard Inshore to also devise a method for recording the conditions at the bottom of the intake as upon dewatering of the plant, audible water flow could be heard from the top of the intake structure but could not be seen. Confined entry into the intake was ruled out because the man platforms and ladders inside the intake shaft had deteriorated with time making them unsafe for their intended use. Hibbard Inshore was able to take the crawler camera, umbilical and lighting and lower it into the shaft in a manner such that the entire shaft could be seen and inspected. The camera identified piping structures at the bottom of the intake that were not on the as-built drawings and identified the source of the leak allowing the customer to keep their people out of a potentially dangerous situation.

Technology Used
Vehicle: Inuktun Crawler ROV System
Camera: Pan and Rotate Color Zoom Video Camera
Lights: Integrated air/water lights, Flood lights
Other tools equipped : 800 foot tether cable