December 18, 2018
AUS was hired to remove a 16-foot diameter, domed, bulkhead in support of the construction for the Lake Mead Intake Number 3, Low Level Pumping Station. The bulkhead had 120 of 3-7/8 nuts that needed to be removed in over 500 feet of water. Options to remove the bulkhead were saturation diving and/or utilizing a ROV with a tooling package. Saturation diving was estimated to be too expensive when compared to the available budget so AUS designed and engineered, in collaboration with another underwater firm, a tooling package to spin off the nuts. This was done with a simple off-the-shelf Stanley IW16 hydraulic impact powered from an 8 gpm mini Stanly hydraulic power unit. The tooling package was connected to a Mohican ROV submersible skid. During trial testing, the tooling package and ROV worked better than expected. In the event the nuts would not come off, were seized, and/or rusted, AUS planned to utilize a dual action, 10,000 psi, Enerpac nut splitter to break the 3-7/8-inch nuts in halves. A separate tooling package was designed and engineered for the nut splitter. Once in the field, the hydraulic impact successfully removed all the nuts without having to split a single nut. The bulkhead, rigged to a 150-ton crane, was successfully slid off the bolts and lifted out of the shaft. The bolts were pushed out of the flange and were allowed to fall to the floor where they were captured in a specially designed net. With the bulkhead removed, the net was then lifted to the surface containing all the nuts and bolts. Operations were scheduled for a total of 15-12 hour shifts and the bulkhead with all nuts were successfully removed in less than 4-12 hour shifts, well under budget.
