Selection of Compatible Materials for use with Terpenes
Use established design guidelines for selection of materials that provide safe operation when exposed to terpenes and other Volatile Organic Compound (VOC's) mixtures.
The use of this data by design engineers will result in the selection of materials for use with terpenes and other VOC's that can provide safe and reliable system operation.
Generally failures in systems using terpenes and other VOC's are caused by: (1) improper choice of materials and/or system components; (2) improper fabrication and assembly practices 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 document.
The design considerations to be used in selection of materials for use laboratory systems in contact with terpenes and other VOC's should consist of:
a) Selection of materials based on property requirements for the application (e.g., strength, thermal properties, oxidizing and corrosive characteristics, etc). b) Selection of materials that can be fabricated without introducing contaminants and/or entrapped voids. c) consideration of effects peculiar to a terpene environment (e.g., terpenes and exposure to friction, solvent presence and compatibility with terpenes, etc).
The design considerations of (b) and (c) above are based on extensive test experience from gaseous and liquid terpene testing conducted at Scientific 710, LLC, and from materials tests conducted at Scientific 710, LLC and other laboratories.
The data for Table 1 was obtained from tests using two techniques, techniques A and 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 to 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 fluorine. 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. GUIDELINE NO. GD-ED-2206 PAGE 4 OF 7 SELECTION OF COMPATIBLE MATERIALS FOR USE WITH FLUORINE Table 2. Compatibility of Materials in Fluorine Aluminum and An aluminum trifluorine (AlF ) film is formed on the surface of the surface of the aluminum metal or alloy. The melting point of aluminum is below its ignition point with fluorine alloys gas. 3 Iron, iron Ferrous and ferric films are formed at a higher rate and depth than other mild resistant alloys, steels metals. Reaction from moisture and hydrogen fluoride is 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, D, Fluoride films are similar to that on aluminum, but are stable for use at high and L), Nickel temperature (1200 F). Welding does not reduce the corrosion resistance of nickel or bearing alloys, Monel if fluxes either are not used or are completely removed. Inconel, Illium, Illium & Monel "R", and Duranickel are less resistant than either nickel or Monel at higher o temperatures but are generally similar to stainless steels. Copper Highly resistant to fluorine attack as are the copper alloys, red brass, and yellow brass. Cupric fluoride film is very stable in the presence of dry fluorine or dry hydrogen fluoride, but hydrolyzes readily in moisture to form hydrofluoric acid. Titanium Poor resistance to hydrogen fluoride. Liquid fluorine has the tendency to be highly reactive with titanium. Gaseous fluorine will attack titanium at temperatures above 300 F. o Silver solder: Recommended for most of the joining where welding is impractical or impossible. Nicrobraze Connections made with this material have been highly reliable. Chromium Four fluorides are formed: 1) divalent, 2) trivalent, 3) tetravalent, and 4) pentavalent (3 an 4 are volatile). When chromium is reacted with fluorine below 300 F it forms a o protective divalent fluoride film. Above 300 F, the fluoride is converted from a o divalent to a volatile tetravalent fluoride form and loses its protective ability. Beryllium Behaves much the same way as nickel in fluoride film formation. Tantalum should not be used at temperatures above 150 Fo Lead Forms a nontenacious fluoride film. In passive exposure it has been used successfully as a seal or gasket material. Tin Reacts similarly to lead and can also be used for soft gaskets in cryogenic service. Rhodium, Can be used on contact with fluorine at room temperature generally without attack. palladium, These metals are used in some equipment because they are inert to hydrogen fluoride. platinum GUIDELINE NO. GD-ED-2206 PAGE 5 OF 7 SELECTION OF COMPATIBLE MATERIALS FOR USE WITH FLUORINE The list in the above table shows a variety of metals which are compatible to a certain degree in fluorine. Generally nonmetallic materials are incompatible with fluorine, with the exception of ruby and Teflon (see References 1 & 3). It should be understood by the designer that material selection is dependent on the environmental conditions. To assist the designer in developing a safe fluorine system, Table 3 lists recommended materials to be used under certain operating conditions. Table 3. Recommended Materials for High and Low Pressure Operations HIGH AND ATMOSPHERIC PRESSURE OPERATIONS Materials Preferred High Pressure: (>14.7-1500 psi.) More resistant to ignition than steel. These metals are Nickel or Monel preferred when handling pure fluorine under pressure. Monel piping can even be used at higher pressures than Nickel. Atmospheric Pressure: If the piping wall thickness is adequate, i.e., as in Copper, Iron, Stainless standard or extra-strong pipe, the material weight and Steel, and Brass surface area are large enough to eliminate spontaneous combustion. High & Low Pressure Through experiments, welding has proved to be highly Connections: reliable in high and low pressure. Soft solder and fluxes Welding, Flange joints should not be used, however. Flange joints are preferred when necessary, gaskets must be limited to soft metals, lead, tin, copper or aluminum. Valves Bellows-sealed valves generally can be used up to 100 psi., in 1-inch and larger sizes. The Hoke Monel needle valves or the Kerotest 440-A packed with Teflon or its equivalent have been successful. Metal-seated valves with Monel or aluminum-bronze seat-and-disk combinations have also been used successfully for low pressure valves. GUIDELINE NO. GD-ED-2206 PAGE 6 OF 7 SELECTION OF COMPATIBLE MATERIALS FOR USE WITH FLUORINE Technical Rationale: Certain effects peculiar to a fluorine environment need to be considered by the designer. Fluorine is a highly reactive oxidizing agent; 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 fluorinated 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 temperature or by providing activation energy from impact, friction, high flow, or reaction of contaminants. 2. Initial pressure of the region. It has been found that ignition temperatures are lowered by increasing 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, surface 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 static 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 on 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 air, is to be avoided. GUIDELINE NO. GD-ED-2206 PAGE 7 OF 7 SELECTION OF COMPATIBLE MATERIALS FOR USE WITH FLUORINE 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 system 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, moisture, 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 cleaning procedures and therefore must be avoided. Impact of Nonpractice: 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.