Storage Temperature Stability

T.O. 33B-1-1 2-34 2.4.4.1.7 Storage Temperature Stability. Storage temperature stability is the ability of a penetrant to resist physical and chemical changes when stored in sealed containers at appropriate temperatures. Penetrant materials, excluding dry developer, SHALL NOT be stored in direct sunlight or at temperatures above 140°F (60°C) or below 0°F (-18°C). 2.4.4.2 Chemical Properties. 2.4.4.2.1 Chemical Inertness. CAUTION Penetrant materials may cause deterioration and damage to materials that react to hydrocarbons. Penetrant materials should not react with the materials to be inspected. It is necessary that the penetrant, emulsifier and developer material be chemically inert relative to the parts being inspected. Most oil base materials meet this requirement. However, water contamination of many oils may cause the mixture to become alkaline. This is one of the reasons why water contamination must be avoided. While oily penetrant materials are generally inert to most metals, there is no one material that can be formulated for all parts. Chemical reactivity of penetrant materials must be considered whenever a new application is encountered. Some rubber (natural and synthetic) and plastic (transparent and opaque) parts are susceptible to attack by the solvents and oils in the penetrant materials. Some metals can be degraded at elevated temperatures by the trace amounts of sulfur or chlorine in conventional penetrants. Special low sulfur and low chlorine materials are available and are discussed in Section 2.8, Special Purpose Materials, paragraph 2.8.3. 2.4.4.2.2 Toxicity. Toxicity is the measure of adverse effects on humans resulting from contact with the material. It applies to any abnormal effects ranging from nausea and dermatitis through dysfunction of major organs, such as the liver or kidneys. It is essential that penetrant materials be nontoxic. In qualifying penetrant materials for the QPL, the manufacturer must submit a certified statement identifying each ingredient in the product by a recognizable chemical or trade name. This information is evaluated for toxicity by the USAF Occupational and Environmental Health Laboratory before the material is listed as a Qualified Product. 2.4.4.2.3 Solvent Ability. The visibility of indications depends upon the fluorescent or visible dye dissolved in the penetrant oils. The oils used in penetrants must have good solvent properties to dissolve and hold the dye in solution. It must maintain the dye in solution under the wide range of temperatures encountered during transit and storage of the penetrant. If even a small amount of separation occurs, recombination may be very difficult or not possible, resulting in decreased penetrant performance. 2.4.4.2.4 Removability. This term describes two conflicting requirements for a penetrant: a) the ability to be removed from a surface leaving little or no residual background and b) resistance to being removed from discontinuities. In order to meet the first requirement, the penetrant must maintain the dyes in solution even when in the form of a thin film on the surface of a part and without its more volatile components that have been lost during the dwell time. This requirement is more difficult for water washable penetrants than postemulsifiable penetrants because the water washable penetrant does not receive the additional solvent or surfactant of the emulsifier/remover during the removal process. The second requirement is met by the penetrant resisting the removal process. For water washable penetrants and postemulsifiable penetrants used with a lipophilic emulsifier, this is accomplished by the formation of a gel with the penetrant/water mixture during washing that protects the penetrant in discontinuities from removal. For postemulsifiable penetrants used with a hydrophilic emulsifier (Method D), the resistance is due to the lack of diffusion of the surfactants into the surface penetrant layer, thus making only the thin surface layer emulsifiable and not the penetrant in discontinuities