ASTM D5854 practice for mixing and handling of petroleum and petroleum products
ASTM D5854 standard practice for mixing and handling of liquid samples of petroleum and petroleum products
7. Handling and Mixing Samples
7.1 General Considerations:
7.1.1 It is preferable that analytical tests be conducted using test specimens which have been drawn directly from the primary container. However, it is recognized that all sampling methods do not permit this nor do requirements to transport and store samples. The number of transfers using intermediate containers between the initial sampling operation and the analytical test should be minimized. Each use of intermediate containers increases the potential for loss of light hydrocarbons, loss of water due to clingage, or inefficient mixing and contamination of the sample from external sources including weather.
7.1.2 Before a sample is transferred from one container to another, a homogeneous mix must be created and maintained until the transfer is completed.
7.1.3 If the sampling procedure requires that multiple samples be taken from a single tank, or in the case of marine vessels, multiple or single samples from multiple tanks, analytical tests may be performed on each sample or on a composite of the various samples. When analytical tests are performed on individual samples, which is the recommended procedure, the test results are generally averaged. Depending on the particular application, the results may be averaged arithmetically or on a volumetrically proportional basis according to the proportion of the total petroleum which the sample represents.
7.2 Composite Samples:
7.2.1 A composite sample may be prepared from individual samples taken from the same tank or, in the case of marine vessels, all tanks that contain the same material. When a composite is required, it must consist of proportional parts from each zone if it is for a single tank. If the composite is for multiple tanks, it must consist of proportional parts from each tank sampled.
7.2.2 Composites normally can be made best in the laboratory. Therefore, samples to be composited should be submitted to the laboratory along with a list of each tank and the volume represented by each sample. The method of compositing should be documented and care taken to preserve the integrity and representativeness of the composite sample.
7.2.3 Making composite samples which will be tested for both density and water or sediment content are especially difficult; the mixing which is necessary prior to compositing for the water or sediment tests can result in loss of light ends which could affect results of the density test.
7.2.4 It is recommended that a portion of each individual sample used in a composite be retained separately (not composited) for retesting if necessary.
7.3 Other Mixing Protocol:
7.3.1 The guidelines herein are intended to cover most sample handling and mixing requirements and should be used for analytical tests unless determined to be unacceptable for a specific application.
8. Sample Mixing Methods
8.1 Sample mixing methods can be divided into three general categories of power mixing, shaking, and no mixing. These categories vary greatly in severity depending on the type of analytical test to be conducted and the characteristics of the sample. The following is a brief discussion of each category:
8.1.1 Power Mixers:
8.1.1.1 Power mixers fall into two general groups of insertion or closed loop. Annex A2 gives the acceptance test criteria for power mixers prior to use. Sample container/mixer systems do not have to be tested individually if they are of the same design and operate within the demonstrated service range (that is, water concentration, viscosity of product, and sample volume).
8.1.1.2 Over-mixing with power mixers may create an oil and water emulsion that will affect the accuracy of certain analytical tests. Power mixers may entrain air into the sample that could affect certain analytical tests. Loss of vapor normally associated with rise in temperature may also occur which could affect tests results for water, RVP, and density.
8.1.1.3 Insertion Mixers - These mixers are stand-alone devices that are not an integral part of a given sampling or mixing system. These mixers can be used on a variety of different types and sizes of sample containers. Non-aerating or high-speed shear mixers are examples of insertion mixers. Insertion mixers may also be of a circulating loop design where a suction port is inserted into the sample container and the sample is circulated externally by means of a pump through a static mixer and discharged back into the sample container through a dispersal system. Annex A3 details the acceptance tests for insertion mixers.
8.1.1.4 Closed Loop Mixers - These mixers are typically used in conjunction with an automatic pipeline sampling system. The mixer may be an integral part of a stationary sample receiver or a stand-alone unit used for portable sample receivers. Annex A4 gives the acceptance testing for closed loop mixing systems.
8.1.2 Shaking - Shaking involves manually or mechanically shaking the sample container to eliminate stratification.
8.1.3 None (no mixing) - If a sample is known to be homogeneous, no mixing is required. Samples should not be mixed where the analytical tests to be conducted may be affected by air which could be induced by power mixing or shaking.
