TO 1-1-700 - Robins Air Force Base

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TO 1-1-700 3.8.7 CRES/Stainless Steel. Basically, stainless steels or corrosion resistant steels (CRES) as they are more properly described, are alloys of iron with chromium and nickel. Many other elements, such as sulfur, molybdenum, vanadium, cobalt, columbium, titanium, and aluminum are added in various amounts and combinations to develop special characteristics. Stainless (CRES) steels are much more resistant to common rusting, chemical action, and high temperature oxidation than ordinary steels, due to the formation of an invisible oxide film or passive layer on the surface of these alloys. Corrosion and heat resistance are the major factors in selecting stainless (CRES) steels for a specific application. However, it should be well understood that stainless (CRES) steels are not the cure-all for all corrosion problems due to service conditions which can destroy the oxide film on their surfaces. Stainless (CRES) steels are highly susceptible to crevice/ concentration cell corrosion in moist, salt laden environments and can cause galvanic corrosion of almost any other metal with which they are in contact if proper techniques of sealing and protective coating are ignored. Stainless (CRES) steels may be magnetic or non-magnetic. The magnetic steels are identified by numbers in the American Iron and Steel Institute (AISI) 400-series, such as 410, 430, etc. These steels are not as corrosion resistant as the non-magnetic steels which are identified by numbers in the AISI 300-series, such as 304, 316, etc. The AISI 300-series steels have nickel contents ranging from 6% to 22%, while the 400-series steels have nickel contents of only 2%. 3.8.8 Nickel and Chromium. Nickel and chromium are used as protective platings. Chromium plating is also used to provide a smooth, wear-resistant surface and to reclaim worn parts. Where corrosion resistance in a marine environment is required, a nickel under-coat is used. The degree of protection is dependent upon plating thickness. Both of these metals form continuous oxide coatings that can be polished to a high luster and still protect not only themselves but also any underlying metal. Chromium platings contain micro-cracks, and corrosion/rust originates on the base metal below these separations and spalls the plating from the surface. Figure 3-22 shows the results of a failed chromium plate. 3.8.9 Silver, Platinum, and Gold. These metals do not corrode in the ordinary sense, although silver tarnishes in the presence of sulfur. The tarnish is a brown-to-black film. Gold tarnish is not really corrosion but is a very thin layer of soils or contaminants that shows up as a darkening of the reflecting surfaces. Silver and gold are used extensively in C-E-M equipment because of their high degree of conductivity and solderability. All these metals are highly cathodic to almost all other metals and can cause severe galvanic corrosion of almost any metal with which they are in contact in the presence of moisture if joint areas are not sealed or otherwise insulated. 3.8.10 Graphite (Carbon) Fiber/Epoxy Composites and Fiberglass Materials. Graphite or carbon fiber/epoxy composites are materials consisting of reinforcing fibers in a matrix of an organic epoxy resin. They are an important class of materials because of their high strength-to-weight ratios and high stiffness. Since carbon is the least active metal in the galvanic series, it will accelerate the corrosion of any metal to which it is coupled; so insulation, usually with sealants, between graphite/epoxy composites and other metals is an absolute necessity to prevent dissimilar metal attack on the attached part. Graphite/epoxy composites are not frequently encountered in C-E-M and associated equipment, but fiberglass materials are used extensively as the foundation of printed circuit/wiring boards and skin panels of vans and shelters. Fiberglass materials consist of a mat of cut glass fibers or a woven mesh of long glass fibers in a matrix of either an epoxy or a polyester resin. Skin panels of some vans and shelters may be fabricated from Kevlar® fiber mesh in an epoxy resin matrix. The fiberglass and Kevlar® materials present no galvanic couple problems, but the joint areas between these types of panels and their metal support frames or structures should be faying surface sealed to prevent fluid intrusion that can lead to corrosion of the metal components. 3.9 CORROSIVE ENVIRONMENTS. Corrosion of C-E-M and associated equipment is caused by both natural and man-made environments. Natural conditions, which affect the corrosion process, are moisture, temperature, salt atmospheres, ozone, sand, dust, solar radiation, insects and birds, and microorganisms. Man-made conditions, which also affect the corrosion process, are industrial pollution, manufacturing operations, storage conditions, and shipment. By understanding these conditions, maintenance personnel will be better able to prevent damage by corrosion. 3.9.1 Moisture. Moisture is present in air as a gas (water vapor) or as finely divided droplets of liquid (mist or fog) and often contains contaminants such as chlorides, sulfates, and nitrates, which increase its corrosive effects. Moisture enters all areas of equipment that air can enter. All enclosed areas that are not sealed allow air to enter and leave as the pressure between inside and outside changes. These pressure changes occur when the atmospheric pressure changes and when the air temperature inside or outside of an enclosed area changes. Moisture condenses out of air when the air becomes too cool to hold all of the moisture in it. The dew found on equipment exterior surfaces, and many times on their interior surfaces, after a cool night is the result of condensation. 3.9.2 Condensed Moisture. Condensed moisture will usually evaporate as surrounding air warms; but its dissolved contaminants, including salts, will be left behind as residues or deposits on the surfaces. This can result in the build-up of soils and salt contamination. Condensed moisture and its con- 3-16
TO 1-1-700 taminants can also be trapped in close fitting wetable joints, such as unsealed faying surfaces as well as in poorly ventilated areas, such as vans and shelters with deactivated cooling systems. Some gasket and packing materials will absorb several times their weight in water and, when heated, can transmit this retained moisture into semi-sealed areas. Moisture can accumulate in such areas through successive cycles of warming and cooling leaving pools of moisture and a relative humidity approaching 100%. This is known as the desert still effect. In addition, moisture can be drawn into poor bond lines by capillary action (wicking). Conditions of temperature and humidity can vary widely in separate sections of equipment, such as vans and shelters and even electronic equipment cases, depending on the success of environmental sealing condensation and location near heat-generating equipment. 3.9.3 Effect of Moisture. Electrolyte formation results from condensation and/or collection of moisture. All non-metals absorb some moisture, which may cause changes in dimensional stability, dielectric strengths, ignition voltages, volume and contact insulation resistances, and conductivities. In general, organic matrix composites, are adversely affected by moisture and may suffer a loss of strength and stiffness from exposure. Hermetic sealing (liquid and vapor proof at normal temperatures and pressures) is recommended for moisture-critical items such as capacitors and quartz crystals. TO 1-1-689-3 is an excellent source for additional information related to electronics equipment. 3.9.4 Temperature. Temperatures at the high end of the range for which equipment is designed may result in either improvement or degradation of equipment operational characteristics. Some electronic equipment may not function properly at high temperatures. Generally, corrosion and other harmful processes (such as the degradation of non-metallic materials) increase as temperatures rise, but in some instances, moderate increases in temperature may serve to reduce corrosion by preventing condensation. Growth of molds and bacteria is also inhibited by temperatures above 104 °F (40 °C). Operation at temperatures near the low end of the design range of below 32 °F (0 °C) generally reduces the rate of corrosion. 3.9.5 Salt Atmospheres. When dissolved in water, salt particles form strong electrolytes. Ocean waters contain from 3.5% to 3.9% salt and are the world's primary source of salt. Normal sea winds carry from 10 to 100 pounds of sea salt per cubic mile of air. Since dissolved salts are strong electrolytes, it is easy to understand why shipboard and coastal environments are highly corrosive. 3.9.6 Ozone. Ozone is made up of three molecules of oxygen instead of the normal two. It is a particularly active form of oxygen, which is formed naturally during thunderstorms by arcing in electrical devices, and by photochemical reactions in smog. When ozone is absorbed by electrolyte solutions in contact with metals, it increases the rate of corrosion. It also oxidizes many non-metallic materials, being particularly harmful to natural and certain types of synthetic rubber. Rubber seals stored near welding equipment have experienced complete degradation. 3.9.7 Other Industrial Pollutants. Carbon (from internal combustion engine exhaust), nitrates (from agricultural fertilizers), ozone (from electrical motors and welding operations), sulfur dioxide (from engine exhaust and industrial and ship smoke stacks), and sulfates (from automobile exhaust) are important airborne pollutants. The combination of these pollutants contributes to the deterioration of non-metallic materials and severe corrosion of metals. 3.9.8 Sand, Dust, and Volcanic Ash. Sand, dust, and volcanic ash are present in many areas. In industrial areas, they often contain a number of tar products, ashes, and soot. Dust is also found in the tropic zones during times of little or no rainfall. Sand and dust are extreme problems in the deserts, since dry, powdery sand and dust are carried by wind. During sandstorms, they can penetrate sealed equipment as well as many internal areas of vans and shelters, and small sand particles are often blown as high as 10,000 feet by the siroccos (hot, dust laden winds). Sand, dust and volcanic ash are hygroscopic (water absorbing) and, when present on internal or external surfaces of equipment or electronic parts, can absorb and hold moisture. The presence of sand, dust and volcanic ash may also affect the operation of electrical contacts, prevent proper action of rotating motor-driven devices, and cause malfunctions of indicating instruments. Dust from volcanic areas contains chlorides and sulfates, which are extremely corrosive in the presence of moisture. Although small amounts of sand or dust may be unnoticed by operating personnel, they may be sufficient to promote corrosion and wear. 3.9.9 Solar Radiation. The two ranges of solar radiation most damaging to materials are ultraviolet, the range that causes sunburn, and infrared, the range that makes sunlight feel warm. On earth, maximum solar radiation occurs in the tropics and equatorial regions, but considerable damage occurs in the temperate zones as a result of solar heating, photochemical effects, and combinations of these two phenomena. Nonmetals, especially organic and synthetic materials, are strongly affected by sunlight. Both natural and synthetic rubber deteriorates rapidly in sunlight. After extended exposure, plastics darken, paints lose their protective characteristics, polymers undergo marked decreases in strength and toughness, and colors fade. This can lead to removal of essential color-coding on tubing and electronic components. Most electronic equipment is housed in enclosed structures and is protected from solar radiation. Extra care must be taken in the selection and surface treatment of parts, such as cables and harnesses that are to be exposed to exterior environments. 3-17
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TO 1-1-700 TECHNICAL MANUAL CORROSI
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TO 1-1-700 TABLE OF CONTENTS Chapte
Page 5 and 6: TO 1-1-700 TABLE OF CONTENTS - CONT
Page 13 and 14: TO 1-1-700 LIST OF ILLUSTRATIONS -
Page 15 and 16: TO 1-1-700 FOREWORD 1. PURPOSE. The
Page 17 and 18: TO 1-1-700 List of Related Publicat
Page 19 and 20: TO 1-1-700 SAFETY SUMMARY 1. GENERA
Page 21 and 22: TO 1-1-700 AMS-G-6032, GREASE, PLUG
Page 23 and 24: TO 1-1-700 MIL-DTL-64159, COATING,
Page 25 and 26: TO 1-1-700 MIL-PRF-27617, GREASE, A
Page 27 and 28: TO 1-1-700 O-L-164, DRESSING, LEATH
Page 29: TO 1-1-700 MIL-T-81772, THINNER, PO
Page 32 and 33: TO 1-1-700 tronics equipment and th
Page 34 and 35: TO 1-1-700 cleaning situation, syst
Page 36 and 37: TO 1-1-700 c. Riveted joints shall
Page 38 and 39: TO 1-1-700 c. Remove and replace an
Page 40 and 41: TO 1-1-700 MIL-L-87177, LUBRICANT,
Page 42 and 43: TO 1-1-700 Figure 3-1. Simplified C
Page 44 and 45: TO 1-1-700 resistant, and also at t
Page 46 and 47: TO 1-1-700 is first noticeable as a
Page 48 and 49: TO 1-1-700 3.7.8 Oxygen Concentrati
Page 50 and 51: TO 1-1-700 Figure 3-14. Concentrati
Page 52 and 53: TO 1-1-700 Figure 3-17. Galvanic Se
Page 54 and 55: TO 1-1-700 Figure 3-20. Aluminum Su
Page 58 and 59: TO 1-1-700 3.9.10 Climate. Warm, mo
Page 60 and 61: TO 1-1-700 3.11 PREVENTATIVE MAINTE
Page 63 and 64: TO 1-1-700 CHAPTER 4 COMPOSITE AND
Page 65 and 66: TO 1-1-700 4.4.4.4 Glass parts shal
Page 67 and 68: TO 1-1-700 CHAPTER 5 PACKAGING (STO
Page 69 and 70: TO 1-1-700 extent of damage dependi
Page 71 and 72: TO 1-1-700 5.15 PRECAUTIONS FOR VCI
Page 73 and 74: TO 1-1-700 c. Secure the desiccant
Page 75 and 76: TO 1-1-700 Figure 5-8. Shock Isolat
Page 77 and 78: TO 1-1-700 Figure 5-9. Examples of
Page 79 and 80: TO 1-1-700 5.24.10 Rigid or Flexibl
Page 81 and 82: TO 1-1-700 CHAPTER 6 MOISTURE AND F
Page 83 and 84: TO 1-1-700 c. 6.2.6 Felt. Examine f
Page 85 and 86: TO 1-1-700 a. After first directing
Page 87: TO 1-1-700 6.4.5.14 Terminals, scre
Page 90 and 91: TO 1-1-700 NOTE • Authorized clea
Page 92 and 93: TO 1-1-700 Table 7-1. Cleaning of S
Page 102 and 103: TO 1-1-700 7.3.1.2.3 Portable, 45 g
Page 104 and 105: TO 1-1-700 Table 7-2. Common Milita
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TO 1-1-700 inactivity, storage, or
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TO 1-1-700 7.5.6.5.1 Grade 1 - A th
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TO 1-1-700 Table 7-4. Corrosion Pre
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TO 1-1-700 Table 7-5. Preservation
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TO 1-1-700 either case, MIL-PRF-269
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TO 1-1-700 MIL-PRF-85285, COATING,
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TO 1-1-700 c. Cadmium plated surfac
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TO 1-1-700 a. Scuff sand and feathe
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TO 1-1-700 7.7.7.2 If surface is no
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TO 1-1-700 7.7.9.2 Where only parti
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TO 1-1-700 7.8.1 Type I Application
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TO 1-1-700 Extend (Loctite) 32150 J
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TO 1-1-700 There are three ways to
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TO 1-1-700 vulnerable surfaces clea
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TO 1-1-700 Table 8-2. Materials, Th
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TO 1-1-700 Table 8-4. Electronic Cl
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TO 1-1-700 Table 8-5. Accessories o
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TO 1-1-700 Table 8-5. Accessories o
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TO 1-1-700 f. Devices with permanen
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TO 1-1-700 Table 8-7. Cleaning and
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TO 1-1-700 MIL-PRF-87937, CLEANING
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TO 1-1-700 of contamination). Maint
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TO 1-1-700 8.8.2 Protective Coating
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TO 1-1-700 • Tube clamps. • Min
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TO 1-1-700 a. For bonding/grounding
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TO 1-1-700 vertently destroy the mo
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TO 1-1-700 doors, and other corrosi
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TO 1-1-700 CHAPTER 10 CORROSION PRO
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TO 1-1-700 MIL-PRF-81733, SEALING A
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TO 1-1-700 d. After corrosion is re
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TO 1-1-700 (3) Stainless/CRES steel
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TO 1-1-700 10.9 WATER ENTRAPMENT AR
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TO 1-1-700 f. Shield equipment from
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TO 1-1-700 b. Use e-inch rivnuts of
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TO 1-1-700 10.17.3 If the plating s
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TO 1-1-700 Figure 10-16. Dissipatio
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TO 1-1-700 (2) If allowable damage
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TO 1-1-700 Table 11-1. Recommended
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TO 1-1-700 11.6 3M CO. SCOTCH-BRITE
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TO 1-1-700 11.11.2 Control of Mecha
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TO 1-1-700 11.12.2 Mechanical Damag
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TO 1-1-700 MIL-DTL-81706 (ALODINE),
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TO 1-1-700 11.13.2.3 Application of
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TO 1-1-700 only when there is no da
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TO 1-1-700 NOTE SEMCO PASA-JELL 101
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TO 1-1-700 (CRES), lead, ceramic, g
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TO 1-1-700 11.13.7.2 Treatment of C
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TO 1-1-700 MIL-A-46106, ADHESIVE/SE
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TO 1-1-700 Table 12-1. Sealing Comp
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TO 1-1-700 used to apply sealants i
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TO 1-1-700 Figure 12-2. Sealant App
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TO 1-1-700 Figure 12-4. Rivet Appli
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TO 1-1-700 Figure 12-6. Sealant Inj
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TO 1-1-700 below and adhere very po
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TO 1-1-700 Table 12-2. Time Require
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TO 1-1-700 Table 12-2. Time Require
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TO 1-1-700 of 20 to 25 seconds in a
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TO 1-1-700 d. Remove all uncured se
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TO 1-1-700 Figure 12-12. Typical Me
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TO 1-1-700 may be used for low temp
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TO 1-1-700 Figure 12-14. Sealing Pr
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TO 1-1-700 - Robins Air Force Base

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