Year after year, maintenance or preventative maintenance (PM) projects are performed for many of UCC’s diverse customer base. Some of these projects are as needed while others are on a formal routine PM schedule. However, at a Midwest power plant, this technical service and approach is anything but routine.
Similar to 2015, (see UCC Blog Article Circulating Water Intake Pipeline – Diving the Depth) the 2018 inspections found significant debris accumulations within the water intake system. In September, following project development and planning, the site moved forward with the debris removal for multiple system tunnels and basins. Diver assisted dredging services were again utilized.
The deep water dive team experienced many of the same challenges faced during the 2015 project. Due to the design and configuration of the system, divers were required to descend the vertical riser 140 feet to the entrance of the tunnels. Each dive required penetration of the tunnel interiors with no direct ascent to the surface. This dive procedure requires the use of an in-water tender at the same depth as the main diver. Furthermore, access into the vertical riser required an additional shallow, in-water tender for each dive. The divers’ visibility never increased beyond 6 inches. The deep dives were completed by surface decompression using oxygen (Sur-D O2).
The material found within the tunnels to be dredged consisted mainly of heavy mud, sand and mussels. On average, the material depth in the tunnels ranged from 4 to 7 feet. In order to maintain suction at the diver’s dredge intake, multiple booster pumps had to be operating in line with the main submersible dredge pump. The dredge slurry was pumped to the processing area over ½ mile away.
While divers ascended back to surface, mixed gas (Nitrox) was used during in-water decompression. Once the deep water divers were back on deck, the on-site recompression chamber was utilized to bring them back to atmospheric pressure.
Preventative maintenance projects may be routine. However, achieving project schedule, budget and performance goals while removing thousands of yards of material, performing hundreds of deep water dives and experiencing zero recordable injuries is routine success for UCC.