Downloaded from http://www.everyspec.<strong>com</strong> on 2011-10-29T14:56:01.DOD-HDBK-791(AM)Figure 8-9. Electromotive Series (Ref. 22)metals. Table 8-3 (Ref. 22) lists the galvanic series for avariety of metals and alloys in sea water. Usually thegreater the separation of two bare metals of this series incontact with each other, the greater will be the corrosionproblem.5. Tank and reservoir drain valves should be locatedso that they maybe removed from the outside to eliminatethe need to enter the tank or reservoir to remove ormaintain the valves.Aircraft drainage presents a particular problem.Drainage should be provided in wings, bodies. and controlsurfaces to prevent the collection of unwanted fluids,including water, from condensation within the aircraft.Consider the following design re<strong>com</strong>mendations:1. Use drain holes in the skin and limberholes in1.2.3.4.5.6.7.8.9.10.11.12.13.14.15.16.17.18.19.20.21.22.23.24.25.26.27.28.29.30.31.32.33.34.35.36.37.38.TABLE 8-3. GALVANIC SERIES INSEA WATER (Ref. 22)MagnesiumMagnesium alloysZincGalvanized steelAluminum (52SH, 61S, 3S, 2S, 53ST in this order)Aluminum clad, 24 ST, 17STCadmiumAluminum (75 ST, A 17 ST, 17 ST, 24ST in this order)Mild steelWrought ironCast ironNi-Resist13% chromium stainless steel, type 410 (active)50-50 lead-tin solder18-8 stainless steel, type 304 (active)18-8-3 stainless steel, type 316 (active)LeadTinMuntz metalManganese bronzeNaval brassNickel (active)Inconel (active)Yellow brassAdmiralty brassAluminum bronzeRed brassCopperSilicon bronzeAmbrac70-30 copper nickelComp. G-bronzeComp. M-bronzeNickel (passive)Inconel (passive)Monel18-8 stainless steel, type 396 (passive)18-8-3 stainless steel, type 316 (passive)bulkheads or stiffeners to permit the unwanted fluids torun to low points when the aircraft is resting in a normalposition.2. Locate drain holes judiciously so that only afew are required and a scavenging suction is produced inflight.3. Where fabric covering is used, install grommetsfor drainage purposes.4. It is sometimes desirable to group a numberof drain lines into a <strong>com</strong>mon outlet to alleviate congestionand to obtain the most direct and efficient routing of lines.To reduce fire hazards, adhere to the following requirements:a. Do not interconnect drain lines for electricalaccessories with lines draining fuel, oil, hydraulicfluid, water-alcohol solution, etc.b. Other accessory drains unless return ofone fluid may damage any of the <strong>com</strong>ponents of these8-14
Downloaded from http://www.everyspec.<strong>com</strong> on 2011-10-29T14:56:01.drains—may be interconnected provided line sizes adequatelyinsure proper drainage.5. Provide adequate ventilation and drainageof all interior areas to prevent the accumulation of toxicor irritating gases, liquids, and explosive mixtures.8-4.3 CLEANING AND PRESERVINGVehicles, weapons, and weapon systems will requirecleaning at some time during their service life. Therefore,equipment should be designed to require a minimum ofmanpower, supplies, and equipment for cleaning, preserving,and refinishing.Equipment ordinarily should not require protectiveprocessing more often than once each six months while instorage. Eliminate requirements for special protection orprocessing for storage by using designs featuring built-incorrosion deterioration protection.8-4.3.1 CleaningExposed surfaces should be shaped to avoid recessesthat collect and retain dirt, water, servicing fluids (spilledin servicing or lost in operation), cleaning solutions, andother foreign materials. Where such recesses cannot beavoided, suitable deflectors and drains should be provided.Where feasible, design equipment to permit the use ofultrasonic cleaning of parts. In addition to speed of operation,ultrasonic equipment has the advantage of eliminatingthe toxic cleaning fluids and the soaking in cleaningtanks containing alkaline solutions. To reduce firehazards, provide tight-fitting metal covers for the petroleumsolvent tanks when they are not in use. Nonflammablesolvents should be used wherever possible.It should be possible to steam clean the external partsof all vehicles, weapons, or weapon systems. This appliesalso to tanks, pumps, valves, filter bodies, accumulators,and cylinders used with <strong>com</strong>mon fuels, exotic fluids, oils,water, air, and gases. Materials not suitable for steamcleaning, such as upholstery and soft linings of vehicles,should be washable with strong detergents and water orwith nonflammable solvents. Consideration should alsobe given to the cleaning, and to the resistance to cleaning,required when, for example, a hydraulic <strong>com</strong>ponent leaksand coats everything in a <strong>com</strong>partment with oil.Engine parts are <strong>com</strong>monly cleaned in alkaline cleaningsolutions <strong>com</strong>pounded for steel <strong>com</strong>ponents. Brassparts, such as block core plugs (freeze plugs), are notseriously affected by alkaline solutions. Aluminum <strong>com</strong>ponents,however, are affected by alkaline solutions and,therefore, should not be used as spacers or brackets.If delicate equipment is located in an area that will besubjected to steam cleaning, the housings should bedesigned to close tightly to insure that steam cleaning orsprayed solvents will not damage the internal <strong>com</strong>ponents.DOD-HDBK-791(AM)8-4.3.2 PreservingConsider the use of preservative materials for the followingitems:1. Surfaces subject to rubbing and chipping2. Fastenings and small parts in hidden locations3. Hidden surfaces whose <strong>com</strong>plex shape or inaccessiblelocation make them difficult to prepare andrefinish4. Small, light parts, such as those made of sheetmetal and other thin-gage materials.Specify ozone-resistant <strong>com</strong>pounding for all rubber<strong>com</strong>ponents that are exposed to the atmosphere. Otherwise,these <strong>com</strong>ponents must be specially preserved duringstorage to prevent deterioration.There is a definite correlation between climate anddeterioration of materials; an unfriendly environmentincreases the maintenance burden. The full range of militaryenvironments is contained in MIL-STD-210 (Ref.23). Tropical climates—characterized by high ambienttemperature and high humidity—present the most severetest for preservation measures. A tropical climate isdefined as one in which the mean monthly temperaturenever goes below 18.2°C (64.9°F). The following majorproblems are associated with tropical areas:1. Corrosion of steel and copper alloys caused byelectrolytic action2. Fungous growth on organic materials such ascanvas, felt, gasket materials, sealing <strong>com</strong>pounds, andeven on the optical elements of fire control equipment3. Deterioration through corrosion and fungousgrowth in insulation, generating and charging sets, demolitionand mine detection equipment, meters, dry cellbatteries, storage batteries, cables, and a variety of lesser<strong>com</strong>ponents.Since fungi can cause corrosion, rotting, and weakeningof materials, materials inert to the growth of fungishould be used whenever possible in the design of USArmy equipment. In general, synthetic resins—such asmelamine, silicone, phenolic, and fluorinated ethylenicpolymers with inert fillers, such as glass, mica, asbestos,and certain metallic oxides—provide good resistance tofungous growth. Not all rubber is fungous resistant, andantifungous coatings generally are impractical for thismaterial. When fungous-resistant rubber is needed, itshould be so specified to insure that the manufacturerfurnishes a suitable <strong>com</strong>pound.Termites attack all wooden parts not impregnated witha repellent agent, and they are especially attracted toplywood bonded with a vegetable glue.Selected materials should be corrosion resistant, orthey should be protected by plating, painting, anodizing,or by some other surface treatment to resist corrosion.Surfaces required to be acid proof should be given additionalsurface treatment. Treatment should be selected inaccordance with MIL-S-5002 (Ref. 24). The use of anyprotective coating that will crack, chip, or scale with ageor extremes of climatic and environmental conditionsshould be avoided.8-15
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