ASTM D6986 Standard Test Method for Free Water, Particulate and Other Contamination in Aviation Fuels (Visual Inspection Procedures)
4. Summary of Test Method
4.1 The test method describes two types of sampling containers for evaluating the appearance of aviation fuel samples. Procedure A covers transparent sample containers, including the open jar and the closed circuit sampler, while Procedure B uses opaque containers such as the white bucket.
4.2 In the open jar procedure, a minimum of 750 mL (24 oz) of fuel is placed into a clear one litre (1 qt) container and examined visually. The jar is then closed and the sample is swirled and examined for visual sediment and water at the bottom of the vortex. Additionally, fuel clarity may be rated by placing a standard bar chart behind the sample and comparing its visual appearance with the standard haze rating photographs. The presence or absence of free water and of particulates is reported.
4.3 In the closed circuit sampler procedure, approximately 3500 mL (0.9 U.S. gal) of fuel is placed into the sampler and is examined for clarity and for visual sediment or water droplets on the bottom of the sampler. Additionally, fuel clarity may be rated by placing a standard bar chart behind the sample and comparing its visual appearance with the standard haze rating photographs. The presence or absence of free water and of particulates is reported.
4.4 In the white bucket procedure fuel to a depth of approximately 15 cm (6 in.) is collected in a white porcelain coated or stainless steel bucket. The sample is examined for solids or sediment, or both, on the bottom of the bucket. Sample clarity can be checked by the appearance of a small, shiny coin on the bucket’s bottom. If the fuel is dry, the raised letters on the coin should be easily readable. The amount of sediment can be described by a letter category using a rating guide.
4.5 In both procedures, the sample is inspected for color or other unusual appearance.
4.6 Field inspection procedures are performed immediately after sampling at fuel handling temperature conditions.
5. Significance and Use
5.1 The two procedures in the test method provide rapid methods for field detection of free water and solid contaminants, or any other visually apparent contamination. Uncertain or marginal results by either of these methods would normally result in the performance of methods such as D2276, D5452, or D3240 for quantitative determination of contaminants.
5.1.1 Particulate determination in appearance tests is sensitive to sampling procedures. The presence of a small number of particles may indicate, for example, that the sample line was not flushed to provide a representative sample. The persistent presence of even a small number of particles, however, may be cause for further investigation depending on the situation.
5.2 Experience has shown that an experienced tester using a clear bottle can detect as little as 40 ppm of free, suspended water in the fuel. Thus, a fuel rated as clear and bright can still fail lower limits set by quantitative methods. A rater will also have difficulty resolving particles smaller than 40 µm. Smaller particles must be determined by other than visual methods such as D2276, D5452 or chemical field tests listed in Manual 5.
5.3 Experience has shown the visual appearance of fuel in a white porcelain bucket to be the most suitable method for the detection of dye contamination or other unusual discoloration. In the U.S., the white porcelain bucket is used to detect the dye.
