ASTM D4740 for cleanliness and compatibility of residual fuels by Spot test
4. Summary of Test Method
4.1 Cleanliness Procedure - A drop of the preheated and thoroughly mixed sample is put on a test paper and placed in an oven at 100°C. After 1 h, the test paper is removed from the oven and the resultant spot is examined for evidence of suspended solids and rated for cleanliness using the D4740 Adjunct Reference Spots.
4.2 Compatibility Procedure - A blend composed of equal volumes of the sample fuel oil and the blend stock is tested in the same way as described in 4.1 and rated for compatibility against D4740 Adjunct Reference Spots.
5. Significance and Use
5.1 The two procedures in this test method are used alone or in combination to identify fuels or blends that could result in excessive centrifuge loading, strainer plugging, tank sludge formation, or similar operating problems.
5.2 A spot rating of Number 3 or higher on a finished fuel oil by the cleanliness procedure indicates that the fuel contains excessive suspended solids and is likely to cause operating problems.
5.3 Although a fuel may test clean when subjected to the cleanliness procedure, suspended solids may precipitate when the fuel is mixed with a blend stock. Evidence of such incompatibility is indicated by a spot rating of Number 3 or higher in the compatibility procedure.
