TO 1-1-700 - Robins Air Force Base

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TO 1-1-700 There are three ways to identify the conformal coating. The easiest and most immediate method is through the relevant system specific technical data. The second method is through chemical laboratory analysis of the coating. The final method is a series of tests as described in Section VI of TO 00-25-234. 8.3.4 Remove the Conformal Coating. Once the coating has been identified it must be removed. It is essential that the coating be identified correctly. If the wrong removal method is attempted on a coating, it can cause serious damage to the component under repair. Methods for removing each type of conformal coating are described in Section VI of TO 00-25- 234. Make sure that the coating is removed completely. There should be absolutely no residue of the coating remaining. 8.3.5 Repair Damage. Once any corrosion and conformal coating have been removed, the component or assembly may be repaired. Any circuit component that has suffered corrosion damage must be removed and replaced. Any circuit card that has suffered corrosion damaged must be repaired if possible. If it is not possible to repair the circuit card such that all functionality is restored, it must be replaced. Detailed instructions for the testing and repair of electronics are given in Section V of TO 00-25-234. 8.3.6 Reapply Conformal Coating. Once all damage as been repaired, the conformal coating must be reapplied to the component. Before the conformal coating is reapplied, the component should be cleaned of any residue from solder flux or other assembly and repair processes, then rinsed thoroughly in deionized water. Approved methods for applying the coatings are given in Section VI of TO 00-25-234. 8.4 ELECTRONIC-SPECIFIC PRINCIPLES AND DESCRIPTIONS. This paragraph is intended to provide information about basic corrosion theory as it applies in an electronics context. Knowledge of the science of corrosion prevention and control is essential when repairing corrosion on electronic components. 8.4.1 Materials and Their Electronic Applications. In order to prevent and recognize corrosion on electronics, it is necessary to know some of the unique applications that materials have in the context of electronics. Table 8-2 gives some of the common uses of various materials in electronics and electronic components. 8.4.2 Corrosive Conditions. Specific conditions that contribute to corrosion are listed in the following paragraphs. 8.4.2.1 Moisture. Moisture is the single most common contributing factor to a corrosive environment. Moisture can gain access either in liquid or vapor form. Any areas where air can access the electronics are potential sources of moisture intrusion. In addition to the corrosive effects of the moisture, it can contain corrosive contaminants such as chlorides, sulfates, and nitrates. 8.4.2.1.1 Moisture whose presence is the result of condensation often evaporates as local temperatures rise. However, this moisture leaves behind residues of contaminants and salts. This residue is especially damaging when it is deposited in close-fitting areas such as faying surfaces. This can happen when the condensed moisture is drawn into close-fitting joints through capillary action. 8.4.2.1.2 In addition to corrosion, moisture contributes to changes in dimensional stability, dielectric strength, ignition voltages, and insulation resistances. 8.4.2.2 Salt. Salts form strong electrolytes when dissolved, which can cause rapid corrosion of metallic materials. The primary source of salt is through water vapor in coastal and shipboard environments. 8.4.2.3 Other Fluids. Fuels, hydraulic fluids, lubricants, and coolants can also contribute to corrosion. Even if the fluids are not corrosive to metals, they can cause damage to sealant materials, which can lead to moisture intrusion in the future. 8.4.2.4 Temperature. Normal operation of communications electronics equipment frequently produces elevated temperatures. The rate of corrosion, out gassing, and decomposition increases as temperature increases. In addition, elevated temperatures can necessitate increased cooling air circulation, which increases the chances of condensation. 8.4.2.5 Pollution. Carbon, nitrates, ozone, sulfur dioxide, and sulfates are some of the pollutants that can be present in the local environments. If these pollutants accumulate, they can combine with moisture to form extremely corrosive solutions. 8.4.2.6 Sand and Dust. Sand and dust can also facilitate the creation of corrosive conditions. Airborne sand and dust enter equipment and settle on all surfaces. Once settled, they can trap and hold moisture, creating the conditions for corrosion to begin. In addition, sand is highly abrasive, which can cause damage if it settles on moving or vibrating parts. 8.4.2.7 Biological Factors (Microorganism, Insect, Animal). Trapped moisture can create the ideal conditions for the growth of molds, bacteria, and fungi. These organisms tend to trap and hold additional moisture. In addition, some of these organisms' secretions are acidic, and thus strong electrolytes. These organisms can feed on nonmetallic materials commonly present in communications electronics. Even “fungus-resistant” synthetic materials can be vulnerable if they are treated 8-2
TO 1-1-700 with a plasticizer or a hardener. The conditions inside electronics assemblies are also very inviting to insects and rodents. These animals can build nests which tend to trap moisture, creating corrosive conditions. Their excrement tends to contain corrosive compounds. Also, insects can feed on electrical insulation, varnishes, and circuit board coatings. 8.4.2.8 Fumes, Vapors, Residues from Assembly Processes. Many common assembly, maintenance, or repair processes produce corrosive by-products. Welding, paint spraying, and solvent cleaning all produce vapors that are corrosive to electronics. If adequate ventilation is not present, these fumes can cause or accelerate the corrosion of electronic components. Also, air conditioned environments can contribute to condensation and the presence of excess moisture. 8.4.2.9 Solder Flux Corrosion. During soldering, flux must be added to remove the protective oxide layers of the metals being joined. Most of this flux is burned away during the soldering operation. However, some flux can remain and must be cleaned immediately. Residues from solder fluxes can damage electronics by: 8.4.2.9.1 Causing soldered joints to corrode. 8.4.2.9.2 Producing corrosive vapors that settle on adjacent components. 8.4.2.9.3 Attacking insulation, reducing its effectiveness. 8.4.2.9.4 Changing the electrical resistance of soldered joints. 8.4.2.9.5 Attracting dirt and other contaminants that can trap moisture and that may be corrosive. 8.4.2.10 Equipment Handling. Equipment removed from its housings for maintenance and repair can become exposed to environments from which it is normally protected. Proper use of protective covers and shipping containers is essential to preventing and minimizing corrosion damage. 8.4.2.11 Packaging. Use of proper materials for packaging is essential for the prevention of corrosion damage. Many common packaging materials (some woods, cottons, foams, and papers, for example) absorb moisture. This makes them vulnerable to mold and fungus attacks, as well as permitting moisture to reach the equipment that they should be protecting. Some glues, paints, varnishes, resins, and preservatives can emit corrosive vapors. Some organic materials (adhesives, gaskets, sealants, wire insulation, sleevings, tubing, plastics, and circuit board varnishes) may outgas corrosive organic acid vapors. If these vapors are released in a confined space (such as inside a container), aggressive corrosion will occur. 8.4.2.12 Storage. Electronic equipment should not be stored in wooden boxes, fiberboard containers, or similar packaging. 8.4.2.12.1 Research and experience have shown that the storage of equipment between 40% and 50% relative humidity (RH) provides a dramatic reduction in corrosion. This drives lower failure rates, reduced repair times, and lower costs. Chapter 6, Sections III and IV of NAVAIR 15-01-500 provide background and instructions on implementing dynamic dehumidification in a facility. This allows for the maintenance of 40% to 50% RH. 8.4.2.12.2 Guidelines for the proper packaging of communications electronics equipment for storage are given in Chapter 5 of this manual. 8.4.2.13 Shipment. During shipment, equipment can be subjected to environments that it would never experience in service. Often, the equipment was not designed to withstand these conditions. This creates an especially acute corrosion hazard. Changes in altitude, temperature, pressure, vibration, and mechanical shocks can all occur with higher frequency and severity than the equipment would normally experience. 8.5 INSPECTION. A comprehensive inspection program is vital to minimizing corrosion damage to communications electronics equipment. Thorough inspection can detect corrosion early, minimizing its operational and financial impact. This paragraph will focus on the inspection of electronic components. For guidance regarding the inspection of mechanical or structural assemblies, consult Chapter 9 of this manual. Corrosion inspections should be scheduled at regular intervals. In addition, any time an electronics enclosure is open for any reason, a spot check should be performed in order to identify any signs of developing corrosion. 8.5.1 Corrosion-Prone Areas. Certain areas of an electronics shelter or enclosure are prone to corrosion. By focusing on these areas, corrosion can be identified more effectively. 8.5.1.1 Moisture and Fluid Intrusion Sources. Any area where moisture is likely to intrude is likely to be prone to corrosion. Examples of such areas include doors, access panels, ducts, seals, gaskets, and bulkhead connectors. Any time water penetrates an enclosure, cables and wiring can direct it to electronics that are especially sensitive to corrosion. 8.5.1.2 Electromechanical. There are many electronic components that contain moving parts. These include switches, relays, potentiometers, motors, generators, and synchro parts. These parts are especially vulnerable to corrosion while in storage. This is because friction tends to keep the 8-3
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TO 1-1-700 TECHNICAL MANUAL CORROSI
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TO 1-1-700 TABLE OF CONTENTS Chapte
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TO 1-1-700 TABLE OF CONTENTS - CONT
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TO 1-1-700 LIST OF ILLUSTRATIONS -
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TO 1-1-700 FOREWORD 1. PURPOSE. The
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TO 1-1-700 List of Related Publicat
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TO 1-1-700 SAFETY SUMMARY 1. GENERA
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TO 1-1-700 AMS-G-6032, GREASE, PLUG
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TO 1-1-700 MIL-DTL-64159, COATING,
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TO 1-1-700 MIL-PRF-27617, GREASE, A
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TO 1-1-700 O-L-164, DRESSING, LEATH
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TO 1-1-700 MIL-T-81772, THINNER, PO
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TO 1-1-700 tronics equipment and th
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TO 1-1-700 cleaning situation, syst
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TO 1-1-700 c. Riveted joints shall
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TO 1-1-700 c. Remove and replace an
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TO 1-1-700 MIL-L-87177, LUBRICANT,
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TO 1-1-700 Figure 3-1. Simplified C
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TO 1-1-700 resistant, and also at t
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TO 1-1-700 is first noticeable as a
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TO 1-1-700 3.7.8 Oxygen Concentrati
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TO 1-1-700 Figure 3-14. Concentrati
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TO 1-1-700 Figure 3-17. Galvanic Se
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TO 1-1-700 Figure 3-20. Aluminum Su
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TO 1-1-700 3.8.7 CRES/Stainless Ste
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TO 1-1-700 3.9.10 Climate. Warm, mo
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TO 1-1-700 3.11 PREVENTATIVE MAINTE
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TO 1-1-700 CHAPTER 4 COMPOSITE AND
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TO 1-1-700 4.4.4.4 Glass parts shal
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TO 1-1-700 CHAPTER 5 PACKAGING (STO
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TO 1-1-700 extent of damage dependi
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TO 1-1-700 5.15 PRECAUTIONS FOR VCI
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TO 1-1-700 c. Secure the desiccant
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TO 1-1-700 Figure 5-8. Shock Isolat
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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
Page 106 and 107: TO 1-1-700 inactivity, storage, or
Page 108 and 109: TO 1-1-700 7.5.6.5.1 Grade 1 - A th
Page 110 and 111: TO 1-1-700 Table 7-4. Corrosion Pre
Page 112 and 113: TO 1-1-700 Table 7-5. Preservation
Page 114 and 115: TO 1-1-700 either case, MIL-PRF-269
Page 116 and 117: TO 1-1-700 MIL-PRF-85285, COATING,
Page 118 and 119: TO 1-1-700 c. Cadmium plated surfac
Page 120 and 121: TO 1-1-700 a. Scuff sand and feathe
Page 122 and 123: TO 1-1-700 7.7.7.2 If surface is no
Page 124 and 125: TO 1-1-700 7.7.9.2 Where only parti
Page 126 and 127: TO 1-1-700 7.8.1 Type I Application
Page 128 and 129: TO 1-1-700 Extend (Loctite) 32150 J
Page 132 and 133: TO 1-1-700 vulnerable surfaces clea
Page 134 and 135: TO 1-1-700 Table 8-2. Materials, Th
Page 136 and 137: TO 1-1-700 Table 8-4. Electronic Cl
Page 150 and 151: TO 1-1-700 Table 8-5. Accessories o
Page 152 and 153: TO 1-1-700 Table 8-5. Accessories o
Page 154 and 155: TO 1-1-700 f. Devices with permanen
Page 156 and 157: TO 1-1-700 Table 8-7. Cleaning and
Page 158 and 159: TO 1-1-700 MIL-PRF-87937, CLEANING
Page 160 and 161: TO 1-1-700 of contamination). Maint
Page 162 and 163: TO 1-1-700 8.8.2 Protective Coating
Page 164 and 165: TO 1-1-700 • Tube clamps. • Min
Page 166 and 167: TO 1-1-700 a. For bonding/grounding
Page 168 and 169: TO 1-1-700 vertently destroy the mo
Page 170 and 171: TO 1-1-700 doors, and other corrosi
Page 173 and 174: TO 1-1-700 CHAPTER 10 CORROSION PRO
Page 175 and 176: TO 1-1-700 MIL-PRF-81733, SEALING A
Page 177 and 178: TO 1-1-700 d. After corrosion is re
Page 179 and 180: 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 MIL-PRF-81733, SEALING A
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TO 1-1-700 MIL-PRF-81733, SEALING A
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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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