Arduous Sea DutyNew Solutions to Top-Side Corrosion Problems Signal an End to Heavy, Maintenance-Intensive Metal Enclosures |
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NAVSEASYSCOM, the engineering service agency of the US Navy has implemented a new Capital Investment for Labor (CIL) program to reduce ship’s force maintenance hours and its Total Cost Ownership for a broad range of on-board systems.
The initiative is now well underway, and Glenair is participating in a major effort focused on stern-gate control panels—the exposed communications and electrical control station located on the stern of LSD class ships. The severe corrosion found on stern gate control panel equipment is indicative of conditions on board a wide variety of Navy ships. Such conditions have resulted in the excessive expenditure of manpower and materials in the never ending task of cleaning up and eliminating endemic corrosion problems. This manpower-intensive task, usually undertaken by untrained personnel inexperienced in proper surface preparation, only covers up the problem and does nothing to eliminate the root cause of corrosion. The process of corrosion is electrochemical in nature (see QwikConnect Vol 7 No 4 Rust Never Sleeps for more details). For the process to occur the following conditions must be met:
The electrical pressure between the two magnetic poles—the anode and the cathode—results in a migration of electrons from one to the other along the metallic path. With the loss of electrons, positively-charged atoms remain at the anode, combining with negatively-charged ions in the environment to form, in the case of steel deck plates, ferrous hydroxide, or rust. In general cases, the role of the ionic current flow is played by the atmosphere and rain, but in marine applications it is the ever-present salt water and spray. The rate at which metal is removed by the corrosive process is usually measured in amperes or thousandths of ampere (milliamperes). In interconnect applications the conductor for this electrical current can be the mating point of the various electrical subcomponents—such as fasteners, bands and braids—or the interface between an enclosure and the bulkhead or panel on which it is mounted. The goal of the CIL program is to identify such sources of corrosion and schedule them for systematic elimination. The stern gate control station, located on the port wing wall at the transom is a corrosion target which is constantly exposed to the elements and periodically to the effects of turbulence caused during LCAC operations. It is an ideal target for innovative solutions to costly corrosion. The station pictured on page 2 had standard Navy electrical and sound powered communication boxes installed, individually attached with welded studs. The electrical cabling is encapsulated within a woven heat resistant fabric to protect it from the hot exhaust anticipated during LCAC operations. The advanced state of corrosion and disrepair at the station, evident from the photographs, is attributable to its location, outdated installation methods and maintenance priorities. The new installation (pictured here on page 3) incorporates the use of a specially-treated, powder coated panel. The surface of the panel was preserved with a special undercoating material followed by additional layers of top coat sealants. Corrosion Engineering Services, Inc. designed and implemented the surface preparation treatments and coatings. A completely new design for the sound-powered communication and electrical junction boxes was designed and developed by Glenair. The design revolved around the use of Glenair CostSaver Composite EMI/RFI Junction Boxes, outfitted with custom lids, indicator lights and other fittings. The Glenair composite boxes were attached to the panel using Glenair 316 stainless steel GroundControl studs (Non-welded). All exposed electrical wiring was encapsulated with high temperature convoluted tubing from the stuffing tube nest to and between the boxes with watertight fittings. The composite thermoplastic components used in the installation—from the junction boxes to the waterproof feed-through fittings and conduit adapters—were all selected for the broad range of material and design benefits they bring to naval applications, including: Corrosion Resistance: One of the most appealing attributes of composites is their unlimited corrosion resistance as compared to conventional materials. Both brass and aluminum boxes, for example, are subject to galvanic coupling which causes the metal material to be “sacrificed” to its plating or to adjacent panels and equipment. Since composite thermoplastics are not sacrificial to plating, finished products last longer, require less maintenance and directly reduce the overall cost of ownership of the system. Weight Reduction: Next to their anticorrosive capabilities, the characteristic of composites that makes them most attractive is their ability to provide increased strength and stiffness at lighter weights than conventional materials. The typical weight savings for composites over aluminum is approximately 40% (depending on component design). Weight savings versus other materials are even more pronounced: 60% for titanium, 80% for stainless steel, and 80% for brass. Vibration Dampening: Another major benefit of composite thermoplastics is vibration dampening. Unlike metals, polymer plastics are less subject to harmonic resonance due to their lighter weight and inherent attenuating properties. Which means threaded components made from these materials are far less likely to vibrate loose when subjected to prolonged periods of vibration and shock. Again, reduced maintenance and reduced cost of ownership are the major benefits realized by systems built from vibration dampening thermoplastics. Stealth: The reduction of magnetic signatures, corrosion related magnetic signatures and acoustic signatures is critical to the development of stealth applications. Signatures are those characteristics by which systems may be detected, recognized, and engaged. The reduction of these signatures can improve survivability of military systems, leading to improved effectiveness and fewer casualties. Composite thermoplastics are at the heart of a number of advanced stealth application development projects. Glenair composite components are ideally suited for use in harsh environments where resistance to saltwater corrosion, high temperatures, outgassing, corrosive fluids, fire, shock and vibration is required. Glenair composites are qualified to the shock, vibration, thread strength and bend moment requirements of MIL-C-38999 and MIL-C-85049. The materials also meet stringent EMI/RFI/HIRF and indirect lightning strike performance specifications. The system of composite junction boxes designed by Glenair for NAVSEASYSCOM was provided as a turnkey installation, fully wired, terminated and tested. Glenair is unique in the industry in its ability to supply the complete system—from the junction and sound-powered boxes to the many varieties of kick-pipe fittings, conduit material, environmental feedthroughs and so on. The photographs on pages 4 and 5 dramatically illustrate the before and after impact of Glenair’s work on the US Naval Sea Systems Command’s CIL Program.
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