PREVENTION AND CONTROL Much has been done over the years to improve the corrosion resistance of newer Navy warships. Improvements include the selection and combination of materials of construction, chemical surface treatments, insulation of dissimilar metals, and protective paint finishes. All these improvements are aimed at reducing maintenance as well as improving reliability. Despite refinements in design and construction, corrosion control is a problem that requires a continuous maintenance program.

With this idea in mind, the NAVSEASYSCOM has developed some excellent ship class corrosion control manuals for you to use as reference tools aboard ship. There are two manuals a GS supervisor should read. They are the Corrosion Control and Prevention Manual f or DD-963 c l a ss ships, NAVSEA S9630-AB-MAN-010, and the Standard Corrosion Control Manual, NAVSEA S9630-AE-MAN-010.

Cleaning As a leading petty officer or work center supervisor, one of your most important aids in the prevention and control of corrosion is an adequate cleaning program. The term clean means to do the best job possible using the time, materials, and personnel available. A daily wipedown of all machinery is better than no cleaning at all. The importance of frequent cleaning cannot be overemphasized. Any cleaning procedures, however, should be in the mildest form possible to produce the desired results. For example, spraying water around multipin connectors can cause electrical shorts or grounds, with a possible loss of control functions or equipment damage.

In general, gas turbine engines and enclosures should be cleaned as often as necessary to keep surfaces free of salt, dirt, oil, and other corrosive deposits. A thorough inspection and cleaning of gas turbine intakes and enclosures should always be done in conformance with PMS requirements. These cleanings and inspections should be done before getting underway, after an extended stay in port, and after returning to port from an extended time at sea.

Since marine gas turbines are more subject to internal corrosion than engines used in other types of applications, internal cleaning is of particular importance. This is accomplished by means of water washing. A mixture of B & B 3100 water-wash compound and distilled water is injected into the engine air inlet while it is being motored and then rinsed with distilled water in the same manner. It is then operated for about 5 minutes to remove all liquid. For more detailed information on this procedure, consult the applicable PMS card.

Characteristics of Metals As a GS supervisor, you should have a thorough knowledge of the characteristics of the various metals used throughout the engineering plant, as well as the engines themselves.

To some extent, all metals are subject to corrosion To keep corrosion to a minimum, corrosion-resistant metals are used to the fullest extent possible consistent with weight, strength, and cost considerations. On exposed surfaces, the major preventive for providing relative freedom from corrosion is a coating of protective surface film. This film can be in the form of an electroplate, paint, or chemicaI treatment, whichever is most practical.

Most of the metals used in the engineering plants require special preventive measures to guard against corrosion. In the case of aluminum alloys, the metal is usually anodized or chemically treated and painted. Steel and other metals such as brass or bronze (with the exception of stainless steels) use cadmium or zinc plating, protective paint, or both. In all cases, the protective finish must be maintained to keep active corrosion to an absolute minimum.

PRESERVATION AND DEPRESERVATION OF GAS TURBINE ENGINES

The main purpose of engine preservation is to prevent corrosion of the various types of materials that make up the engine and its accessories. Preservation also ensures against gumming, sticking, and corrosion of the internal passages.

Engine preservation and depreservation is vital because the corrosion of engine structures can and does have a great effect on the operational and structural integrity of the unit. Therefore, it is important that you know about methods of preservation, materials used, and depreservation procedures.

PRESERVATION AND PACKAGING FOR STORAGE If you know that an engine is to be shipped or stored, you must make plans to preserved it prior to removal from the ship. Engines to be taken out of operation for periods of up to 1 month require only that the unit be protected from the elements. Units that will be stored or out of service for more than a month must be preserved for storage.

Packaging for storage should comply with current instructions for engine shipment furnished by the manufacturers. If specific manufacturer's instructions are not available, then the engine should be placed in a hermetically sealed metal container with a humidity control and an external humidity indicator.

All major engine parts, no matter how badly worn or damaged, must be returned with the engine whether it is to be overhauled or salvaged. Remember, the entire assembly (engine and accessories) must be protected from damage during shipment. When preparing the engine for shipment, you must be sure that all fuel lines, receptacles, oil lines, intakes, exhausts, and any other openings in the engine or its components are capped or covered before the engine is removed.

For further information, packaging requirements are given in MIL-E-17341, MIL-E-17555, and MIL-E-17289.

DEPRESERVATION An engine that has been in storage, or inoperable for an extended period of time, must be depreserved before it can be placed in service. Before connecting the engine to the external portion of the fuel and oil system (supply tank, coolers, falters, and so forth), the external tubing and equipment must be thoroughly flushed and purged. After installation, fill the oil sump (Allison) or LOSCA (LM2500) with clean lubricating oil to the proper operating level.

CAUTION To prevent accidental firing, ensure that the engine ignition circuit is disconnected when priming the fuel control and the fuel system.

Before initial operation, the engine fuel system must be flushed and purged. To accomplish this, the engine is motored until all bubbles are out of the fuel stream and only fuel comes through. While motoring, observe the engine oil pressure. If no pressure is indicated, the cause must be determined and corrected before the engine can be started. In all cases, the manufacturers' technical manual must be consulted for specific instructions on the depreservation and start-up of each particular engine.