ASTM D7112 for stability and compatibility of heavy fuel oils and crude oils
ASTM D7112 Standard Test Method for Determining Stability and Compatibility of Heavy Fuel Oils and Crude Oils by Heavy Fuel Oil Stability Analyzer (Optical Detection)
4. Summary of Test Method
4.1 Stability and compatibility parameters are determined by titration and optical detection of precipitated asphaltenes. A stock solution is prepared and three different mixtures of the sample oil plus xylene are titrated with n-heptane to cause precipitation of asphaltenes. The titrated mixture is continuously circulated through an optical detector which detects precipitated asphaltenes by back-scattering of visible light. The amounts of oil, xylene, and n-heptane are used to calculate stability parameters: solvent equivalent, P-value, and FR5/1. If the density of a crude oil sample is known, then the compatibility parameters (SBN and IN) of the crude oil may also be calculated.
5. Significance and Use
5.1 Automatic determination of stability parameters using a light back-scattering technique improves accuracy and removes human errors. In manual testing, operators have to visually compare oil stains on pieces of filter paper to determine if asphaltenes have been precipitated.
5.2 Refinery thermal and hydrocracking processes can be run closer to their severity limits if stability parameters can be calculated more accurately. This gives increased yield and profitability.
5.3 Results from the test method could be used to set a standard specification for stability parameters for fuel oils.
5.4 The compatibility parameters of crude oils can be used in crude oil blending in refineries to determine, in advance, which crude oil blends will be compatible and thus can be used to minimize plugging problems, unit shut downs, and maintenance costs. Determination of crude oil compatibility parameters also enables refineries to select crude oil mixtures more economically.
5.5 This test method can measure stability and compatibility parameters, and determine stability reserve on different blends for particular applications to optimize the blending, storage, and use of heavy fuel oils
NOTE 1 - Users of this test method would normally use stability and compatibility parameters to determine stability reserve of residual products, fuel blends and crude oils. However, the interpretation of stability, stability reserve and compatibility is heavily "use dependent", and is beyond the scope of this test method.
6. Interferences
6.1 Free water present in the oil can cause difficulties with the optical detector and should be removed by centrifuging prior to testing.
6.2 Solid particles, such as coke or wax particles, mud, sand, or catalyst fines, in the oil will not affect the optical detector or interfere with the results.
