Global Diving & Salvage,Inc was contracted by Salt River Project (SRP),operator of Horse Mesa Dam,located 65 miles northeast of Phoenix,AZ,to provide project management and diving services to make repairs of Units 1 through 4. The work on Unit 4,located in 160 feet of water,and on Units 1,2,and 3,located in 260 feet,necessitated the use of saturation divers.
Saturation diving is a method where divers live at a pressure equal to the depth they are working and transit to and from the work area via a diving bell. When not working,they live in chambers that are located on the deck of the barge. A crew of 21 working in two 12-hour shifts are required to support both the divers on deck and those in the water. In saturation diving,decompression is not eliminated; it is delayed until their rotation is over,which is usually 30 days. On this project,it took three days to decompress from the working depth to the surface.
In June 2012,a vertical concrete guide vane located in Unit 4 failed. Divers removed the remaining sections of the damaged vane as well as a second still-intact vane,using wire saws and wall saws. A new steel vane system,consisting of two vertical and nine horizontal vanes,was installed in place of the original concrete structures. The vanes were bolted in place and then filled with grout for added stability. New trashracks were installed in the intake. The bulkheads for Units 1,2,and 3 did not seal adequately to the penstock intakes due to deteriorated concrete on the intake opening face. Divers anchored and sealed new steel sealing frames at each intake location. Inspection also discovered deteriorated concrete at various locations in the three sets of gate guide slots on the upstream face,which was repaired.
We conducted this saturation dive project in the Gulf of Mexico to recover debris,BOP,and salvage jack-up legs. Burning,hot-tap operations,rigging,and survey operations were completed. Work was done at approximately 300 feet.
This saturation diving project included the removal of structural debris,as well as wedding cake and wellhead operations. The work was conducted across six platforms with 29 wellhead installations,ranging in depth from 120-280 feet of sea water (fsw).
Our work was performed in 285 feet of water and at an elevation of 7,300 feet using saturation diving techniques. Tasks included furnishing,installing and grouting in place 47 feet of concrete jacking pipe to form a structural liner in an existing inlet tunnel. An 18-ton stainless steel inlet gate was installed within very tight tolerances. Stainless steel hydraulic lines were fabricated and installed from the crest of the dam to the gate,which included anchoring pipe brackets along the steeply sloped and highly irregular reservoir floor. The existing trash racks were modified along with the installation of new trash rack components to facilitate the installation of the gate valve. Work was completed during a single 50-day saturation diving run.
An innovative system of winches and track allowed the large-diameter sections of steel reinforced pipe to be positioned into place with exact precision. Each pipe segment was advanced through the tunnel using a hydraulic jacking sled designed to mate with the bell end of the pipe segments. A steel jacketed thrust collar located at the downstream end of the liner resists thrust from the closed gate. The thrust collar was installed,grouted in place and then anchored to the existing substrate using rock anchors. Holes for the anchors were core drilled using a hydraulic drill mounted to a circular track system designed to be attached to the interior of the thrust collar,allowing a 360-degree drilling angle. Pre-job engineering enabled complex construction tasks to be performed at depths approaching 300 feet.
We were selected to supply saturation diving services aboard the DSB BOA Deep C,a DP III (Dynamically Positioned Vessel),in the Gulf of Mexico.
The project included removing existing structures,wedding cake wells,and installing wellheads.
The work was performed on four different platforms,and involved installing 57 wellheads and removing 5,800 metric tons of structures.
The operation involved 21 persons operating 24/7 in support of around-the-clock diving activity in depths of 160-270 feet of water.