1、Best Practices Entry: Best Practice Info:a71 Committee Approval Date: 2000-03-09a71 Center Point of Contact: GRCa71 Submitted by: Wil HarkinsSubject: Selection of Compatible Materials for use with Fluorine Practice: Use established design guidelines for selection of materials that provide safe opera
2、tion when exposed to elemental fluorine and fluorine-oxygen (FLOX) mixtures.Programs that Certify Usage: N/ACenter to Contact for Information: GRCImplementation Method: This Lesson Learned is based on Reliability Guideline Number GD-ED-2206 from NASA Technical Memorandum 4322A, NASA Reliability Pref
3、erred Practices for Design and Test.Benefit:The design data provides a list of materials and conditions which are compatible for use with fluorine. The use of this data by design engineers will result in the selection of materials for use with fluorine that can provide safe and reliable system opera
4、tion.Implementation Method:Generally failures in systems using fluorine are caused by: (1) improper choice of materials and/or Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-system components; (2) improper fabrication and assembly practices, (ref 1)
5、; and (3) improper system preparation and operating procedures, resulting in the presence of contaminants. This guideline applies design considerations to preclude failures caused by improper choice of materials. Design guidelines to address failure causes (2) and (3) are beyond the scope of this do
6、cument (see Reference 1).The design considerations to be used in selection of materials for use in fluorine systems should consist of:a. Selection of materials based on property requirements for the application (e.g., strength, thermal properties, welding or brazing characteristics, etc). Note: This
7、 design consideration represents standard design approach and is presented here for completeness onlyb. Selection of materials that can be fabricated without introducing contaminants and/or entrapped voids.c. Consideration of effects peculiar to a fluorine environment (e.g., ignition temperature of
8、material in fluorine, fluoride films and exposure to friction, moisture presence and compatibility with hydrogen fluoride, etc).The design considerations of (b) and (c) above are based on extensive test experience from liquid fluorine rocket testing conducted at LeRC, and from materials tests conduc
9、ted at LeRC and other laboratories.References 1, 2, and 3 present material compatibility with liquid fluorine for metallic and nonmetallic materials, respectively. Table 1 below, extracted from reference 1 and presented here for purposes of illustration, lists the ignition temperatures and ignition
10、delays for metals in fluorine.Table 1. Ignition Temperatures of Metals in Fluorine (a) Technique A Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Metal Wire diameter, in.Ignition temperature, CAverage ignition temperature, CMax variation from averag
11、e, percentAluminum 0.010 0.016- (a) -Copper 0.0123 645 to 747 692 8.0Iron 0.014 667 to 677 672 0.8Molybdenum 0.0149 188 to 220 205 8.3Monel 0.010 348 to 437 396 12.0Nickel 0.008 0.0155 0.0154 0.01521168 1096 1219 10841162 6.0Stainless Steel 302 0.020 570 to 796 681 13.0Tungsten 0.0153 260 to 332 283
12、 18.0Table 1. Ignition Temperatures of Metals in Fluorine-Concluded (a) Technique B Metal Wire diameter, (in)Max wire temperature CIgnition delay, secIgnition temp range CActivation energy, kcal/moleCopper 0.012 905 852 810 767 701 6890.8 1.0 0.6 0.8 1.2 No ignition689 to 701 39.5Iron 0.014 730 676
13、648 644 6181.0 1.6 2.0 2.2 No ignition618 to 644 16.3Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Nickel 0.015 1357 1306 1266 12530.6 1.2 0.6 No ignition1253 to 1266-The data for Table 1 was obtained from tests using two techniques, techniques A a
14、nd B. In technique A, an evacuated bomb was filled with gaseous fluorine at atmospheric pressure and the fluorine was increased in temperature by a heated wire. The temperature at which the wire burned is listed in the part of Table 1 for technique A. In technique B, the evacuated bomb was brought t
15、o temperature before fluorine introduction. The time required for the reaction to go to completion, the ignition delay, is listed in the part of Table 1 for technique B.In addition, Table 2 was produced from Reference 1 which shows an expanded list of materials and their reactive effects with fluori
16、ne. Reference 1 also includes the effects of the presence of water and corrosion, the effects of fluoride films and their characteristics, and specific reaction of fluorine spills.Table 2. Compatibility of Materials in Fluorine Aluminum and aluminum alloysAn aluminum trifluorine (AlF3) film is forme
17、d on the surface of the surface of the metal or alloy. The melting point of aluminum is below its ignition point with fluorine gas.Iron, iron alloys, steelsFerrous and ferric films are formed at a higher rate and depth than other mild resistant metals. Reaction from moisture and hydrogen fluoride is
18、 also greater.Stainless steels Resistant to attack by hydrogen fluoride is greater than most mild steels. A fluoride film is formed with characteristics equivalent to Monel. The film becomes less stable at elevated temperature. Stainless steel welds behave similarly as the parent material.Nickel (A,
19、 D, and L), Nickel bearing alloys, it has the highest oxidation potential of all elements. Fluorine can react with practically all organic and inorganic substances with few exceptions. Exceptions include the inert gases, fluorinated compounds in their highest state of oxidization, and a few fluorina
20、ted polymers.Whether a substance will burn spontaneously in fluorine, or whether fluorine will replace an oxidant having a lower oxidizing potential, depends on the following conditions of exposure, (Reference 1):1. Initial temperature of the region. Reaction is initiated by reaching the ignition te
21、mperature or by providing activation energy from impact, friction, high flow, or reaction of contaminants.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-2. Initial pressure of the region. It has been found that ignition temperatures are lowered by i
22、ncreasing pressure.3. Thermal conductivity if the material is a solid. Combustion will not occur if heat of reaction can be removed by conduction and the temperature can be maintained below ignition temperature of material.4. Exposed surface area with respect to mass of the substance. Generally, sur
23、face reactions with most metals will form a fluoride film and inhibit further reaction. Large exposed surface-area-to-mass material forms (fine mesh screen, powered metal, etc.) can have surface reactions that are highly reactive and can increase temperatures to initiate combustion.5. Kinetic or sta
24、tic exposure. It has been found that kinetic energy from flow dynamics can contribute to activation energy for combustion.6. Fluorine concentration in the region. Reactivity increases with increased fluorine content of liquid or gaseous mixtures.Fluorine can react combustively with water depending o
25、n the size of water droplets. Ice will react combustively with liquid fluorine. In the presence of water, the fluorine will react to form hydrogen fluoride potentially resulting in corrosion. Therefore, the entry of water into the system in any form, even from non-dry purge gases or moisture laden a
26、ir, is to be avoided.In addition to the selection of materials based on property requirements for the application (i.e. strength, thermal properties, welding or brazing characteristics, etc), the selection of materials for use with fluorine must consider the introduction of contaminants into the sys
27、tem and whether a given material will burn spontaneously in the presence of fluorine. Materials selected must be cleaned free of contaminants and fabricated without introducing contaminants and/or entrapped voids. The contaminant can be in the form of a material additive or foreign material (ice, mo
28、isture, grease, soil, etc.) which unintentionally enters the system. The contaminant can then react with fluorine and cause local temperatures to exceed the ignition temperature for that part of the system, resulting in failure. The presence of voids can lead to trapped contaminants that escape clea
29、ning procedures and therefore must be avoided.References:1. Schmidt, H. W.: “Fluorine and Fluorine-Oxygen Mixtures in Rocket Systems,“ NASA SP-3037, 1967.2. Schmidt, H. W.: “Compatibility of Metals With Liquid Fluorine At High Pressures and Flow Velocities,“ NACA RM E58D11, 1958.3. Price Jr., H. G.
30、and Douglass, H. W.: “Nonmetallic Material Compatibility With Liquid Fluorine,“ NACA RM E57G18, 1957.4. Slesser, Ph.D. Charles and Schram, Stuart R.: “Preparation, Properties, and Technology of Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Fluorine
31、 and Organic Fluoro Compounds,“ McGraw-Hill, New York, 1951.Impact of Non-Practice: Failure to use the design data presented in this guideline will result in unsafe systems and failures which are costly and potentially injurious to personnel and environment.Related Practices: N/AAdditional Info: Approval Info: a71 Approval Date: 2000-03-09a71 Approval Name: Eric Raynora71 Approval Organization: QSa71 Approval Phone Number: 202-358-4738Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
