Aviation fuel corrosion

Finally, other tests to control jet fuel corrosivity towards certain metals (copper and silver) are used in aviation. The corrosion test known as the copper strip (NF M 07-015) is conducted by immersion in a thermostatic bath at 100°C, under 7 bar pressure for two hours. The coloration should not exceed level 1 (light yellow) on a scale of reference. There is also the silver strip corrosion test (IP 227) required by British specifications (e.g., Rolls Royce) in conjunction with the use of special materials. The value obtained should be less than 1 after immersion at 50°C for four hours. 

The aluminium coatings are highly corrosion resistant, and are less liable to contact corrosion than cadmium when in contact with light alloys. They can also be used at temperatures of up to 496°C as against 232°C for cadmium. The aluminium coating is also unaffected by aviation fuels, unlike cadmium. 

Failure of sensitive filtration tests such as ASTM D-2276, Particulate Contamination in Aviation Fuel by Line Sampling, can be due to caustic neutralized corrosion inhibitor salts. Sodium or calcium salts of dimer-trimer fatty acid corrosion inhibitors are gel-like in character. Filtration of jet fuel containing gelled corrosion inhibitor will be impeded due to plugging of fuel filter media by the inhibitor gel. This slowdown of filtration can result in failure of jet fuel to pass this critical performance test. 

Test method ASTM D-2276, Particulate Contaminant in Aviation Fuel by Line Sampling, requires filtration of fuel through a 0.8-micron filter. Caustic neutralized corrosion inhibitor salts can block these filters and slow down the filtration of fuel enough to cause failure of this ASTM test. 

Jet fuels are aviation fuels used mainly by the United States and other North Atlantic Treaty Organization (NATO) nations for military establishments. Other fuels called Jet A and Jet A-1 are closely related fuels used by commercial airlines. JP are a complex mixture of primarily aliphatic (but also aromatic) hydrocarbons, derived from crude oil and/or kerosene by refining and adding various other additives such as fuel icing inhibitors, antioxidants, corrosion inhibitors, metal deactivators, and static dissipaters. Gas chromatographic analysis of JP-8, the most recent JP, indicates that it is made up of complex mixture of 9 to 17 different hydrocarbons, including thousands of isomers and three to six performance additives. They are generally colorless liquids and smell like kerosene. 

Although the type and amount of each additive permitted in aviation fuels are strictly limited to color dye, antioxidant, metal deactivator, corrosion inhibitor, fuel system icing inhibitor, static dissipator, and lubricity additive, test methods for checking the concentration present are not specified in every case. In some cases tests to determine the additive content (or its effect) are called for, but in other cases a written statement of its original addition (e.g., at the refinery) is accepted as adequate evidence of its presence. 

After the required amounts of antioxidant, metal deactivator, or corrosion inhibitor have been added to aviation fuels it is not normal to carry out any checks on the concentrations, and no test methods are included in specifications for this purpose. Occasionally a need arises to determine the amount of corrosion inhibitor remaining in a fuel, and several analytical methods have been developed, none of which has yet been standardized. 

As a valuable step toward rationalizing the approval procedure for aviation fuel additives, guidelines are available (ASTM D-1655, ASTM D-4054).Tests are available for measuring or specifying additives such as color dyes (ASTM D-156, ASTM D-2392, ASTM D-5386, IP 17), corrosion inhibitors (often measured by the corrosivity of the fuel— ASTM D-130, ASTM D-5968, IP 154), lubricity (ASTM D-5001), fuel system icing inhibitors (ASTM D-910, ASTM D-4171, ASTM D-5006, IP 277), and static dissipator additives (ASTM D-2624, ASTM D-4865, IP 274). 

Acids can be present in kerosene aviation turbine fuels because of acid treatment during rehning. These trace acid quantities are undesirable because of the possibility of metal corrosion and impairment of the burning characteristics and other properties of the kerosene. The potential for metals in kerosene is less than it is for aviations fuels, but several of the same tests can be applied (Chapter 6). 

Copper corrosion of aromatics 0873, Oxidation stability of aviation fuels X X ... 

When sampling aviation fuel. Practice D4306 diould be consulted for recommended cleaning procedures for containers that are to be used in tests for the determination of water separation, copper corrosion, dectrical conductivity, thermal stability, lubridty, and trace metal content. 

Corrosion Inhibitor - helps prevent rusting of metal engine components. Also, corrosion inhibitors provide a protective film on metal surfaces to aid in improving the lubricating properties of jet fuel. Use is not permitted in aviation gasoline and civil jet fuels, but is mandatory in military jet fuel grades. 

The requirements for jet fuels stress a different combination of properties and tests than those required for aviation gasoline (ASTM D-1655). The same basic controls are needed for such properties as storage stability and corrosivity, but the gasoline antiknock tests are replaced by tests directly and indirectly controlling energy content and combustion characteristics. However, as with other petroleum products, application of sampling protocols (ASTM D-3700, ASTM D-4057, ASTM D-4177, ASTM D-4306, ASTM D-5842) is of prime importance. 

Tertiary amines have unusually low viscosities, are more soluble in petroleum solvents, and are more selective and more stable than non tertiary amines [100], These amines are corrosion inhibitors and are intermediates in the preparation of materials coating, plastics, textile, paper, and leathers [101]. They are used as precursors of agricultural chemicals, like herbicides and insecticides, pharmaceutical and therapeutic agents, and in fuel oil additives such as aviation jet fuels, gasoline, and in lubricants [102]. 

A major need within this Department has been the determination of commercial additives based on dimer acid (dilinoleic acid), used as pipeline corrosion inhibitors and anti-wear additives in aviation turbine fuel [47]. Quantitative determination of the 15-25 ppm level in fuel was solved by aqueous alkaline extraction from the fuel, followed by acidification and extraction into chloroform. After washing with water and evaporation of the bulk of the chloroform, the residue was made up to 10 mL volume and injected on to a single 100A Styragel column. A detection limit of Ippm additive (c 0.5 ppm dimer acid) was easily achieved using refractive index detection. 

This test method covers the detection of the corrosiveness to copper of aviation gasoline, aviation turbine fuel, automotive gasoline, natural gasoline or other hydrocarbons having a Reid vapor pressure no greater than 18 psi (124 kPa) (Caution—see Note 1 and Annex A2.), cleaners (Stoddard) solvent, kerosine, diesel fuel, distillate fuel oil, lubricating oil, and certain other petroleum products. 

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