Automating Dry Docks in the Pacific
A new automated supervisory control and data acquisition system for Pearl Harbor Naval Shipyard in Hawaii is being used to control a network of actuators and Motor Operated Valve assemblies—helping provide safe control of the water flow for maintenance and operations workers on nuclear submarines in dry dock.
By Ed Nugent
Pearl Harbor Naval Shipyard and Intermediate Maintenance Facility, Dry Dock Number 2. IMAGES COURTESY PCVUE INC.
Adjacent to Honolulu on Oahu’s south shore, Hickam Air Force Base and Pearl Harbor Naval Station have a long association with the historic port Wai’Momi, as it is known to the native Hawaiians. The Pearl Harbor Naval Shipyard and Intermediate Maintenance Facility, located at Joint Base Pearl Harbor-Hickam, Hawaii, is a one-stop regional maintenance center for U.S. Navy surface ships and submarines. It is the only intermediate maintenance facility for submarines in the Middle Pacific.
Of the four dry docks at Pearl Harbor, Dry Dock Numbers 1, 2 and 3 are located in the Controlled Industrial Area and are primarily used for repairing and maintaining nuclear submarines. These are graving style dry docks comprised of a narrow basin with access to deep water through a floating caisson gateway. Dry Dock Number 1 measures 1,001-ft from the head side of the caisson, with a width of 114-ft at the bottom and 138-ft at the top, and a depth of 32-ft, 6-in from the mean high water mark to the keel blocks.
To access the dry dock, a ship is floated into the basin, the caisson is positioned at the seaward side and the dock basin is dewatered with large vertical turbine pumps. As the basin empties, the pressure of the sea against the caisson creates a watertight seal and allows the ship to come to rest on a dry platform. Dry dock operators manage this process, known as evolution, with a staff of engineers, electricians and operators. These technicians are responsible for the safe movement of equipment and water in order to ready the dry dock for ship maintenance and repair.
Triton Marine Construction Corp. is a waterfront multiple award construction contractor for Naval Facilities Engineering Command. In 2012, the firm was awarded a task order for improvements to Dry Dock Number 1, which included upgrading the actuators and installing a valve control system. A type of supervisory control and data acquisition (SCADA) platform had been in operation for all three dry docks in the Controlled Industrial Area, including Dry Dock Number 1, however, the operations staff had not been satisfied with the safety, reliability and performance of these existing systems. These concerns prompted the discontinuation of that system, which forced the operations personnel to go back to more labor-intensive manual operations. A new kind of SCADA system was needed.
Dry dock operators are prohibited by the SCADA from performing valve movement until receiving the Ready for Operation indicator.
PcVue Inc. would be commissioned as part of the Dry Dock Number 1 upgrade in 2012 to install a new SCADA. PcVUE’s automated SCADA system, since installed and in operation, is primarily controlling a network of Limitorque actuators. The actuators are assembled on large gate valves and the assemblies are known as a Motor Operated Valves (MOVs). The SCADA communicates with the MOVs using redundant Modbus IP networks that are connected to a redundant gateway. A Modbus serial 485 loop connects the actuators with the gateway.
The dry dock is controlled by 19 MOVs with 16 I/O points being monitored and controlled per actuator. This fault tolerant system opens and closes valves to precise percentages and adheres to specific dry dock operational valve position protocols for safe control of water flow. Dry dock operators are prohibited by the SCADA from performing valve movement until receiving the Ready for Operation indicator. This indicator is a synthesized status that is derived from monitoring multiple alarm points including power off, over-temperature, over-torque, jammed valve and other actuator alarm conditions. PcVue’s event historian keeps an ongoing log of the control actions as an audit trail.
Valve Control System - Dry Dock Number 1
BUILDING ON SUCCESS
Upon completion of the Dry Dock Number 1 project—and after firsthand experience with PcVue—the Navy was able to confirm that the reliability and performance issues were mitigated. The success of the project opened the door for SCADA upgrades at the other two docks in the Controlled Industrial Area.
Most importantly, the PcVue system had eliminated the safety concerns. While safety is important in any process, the large amount of water flowing through chambers at the dry dock could put operations personnel and shipyard workers in harm’s way if not carefully controlled.
Subsequently, the shipyard did elect to retrofit the SCADA in Dry Dock Numbers 2 and 3. A request-for-proposal was issued for the troubleshooting and upgrading of the control system. The system integrator replaced the SCADA and was able to leverage the object-oriented reusability features of PcVue and minimize the bid cost by using common objects developed for Dry Dock Number 1. The retrofit for the other two docks was completed in a matter of a few weeks in 2013.
The new dry docks were commissioned to be identical to the previous ones’ control systems. This allowed the operations to accommodate the new system with the same certified process. The same graphical display was utilized, too, so that minimal operator training was required, which kept expenses down.
There were multiple MOVs to control. But by utilizing the Application Architect feature from PcVue with symbols and branching, both the configuration time and the possible points of human error on configuration were minimized. The team developed objects to Pearl Harbor Naval Shipyard standards, including animated graphical objects (such as symbols and mimic templates), which provided a consistent graphic and navigation look and feel. PcVue’s branching concept minimized the number of mimics required by invoking the graphics and all the variables and tags that were tied to it in the context of the MOV to be controlled.
By reusing and applying the same configuration objects that had been developed for Dry Dock Number 1 for the subsequent upgrades to Dry Dock Numbers 2 and 3, the installation was able to save both money and time.
UPGRADES WITH AN IMPACT
Pearl Harbor Naval Shipyard has been pleased with the results of the MOV control system upgrades. The operational needs of the dry dock personnel have been exceeded while meeting the commitment of the project specifications. The team has been very happy with the flexibility of the application and adaptations to its specific requests—often needed in very short timeframes.
Even with the rigorous requirements of the Navy, the project has gone smoothly. And most importantly, the shipyard engineers and operators are able to effectively and safely perform their responsibilities. For a nuclear submarine maintenance facility, is there anything more important?