2.3.5 Tap Samples Some tanks have sample taps for sampling. When possible, it is preferable to take spot samples from the top of the tank, since the taps are usually fixed and therefore do not sample from the middle of each third of the product. Tap samples must always be clearly labeled with the height of the tap and the height of the liquid in the tank. Tap samples are not usually used for custody transfer purposes and are taken only when specifically requested by your supervisor. 2.3.6 Manual Pipeline Sampling Manual pipeline sampling is not recommended for custody transfer because automatic pipeline sampling is superior to the manual method. Most manual pipeline samples are spot samples that are taken for quality control purposes, during a movement. When manual pipeline sampling becomes necessary, the samples require labeling with the exact time the sample is taken, and a pumping log of the transfer obtained to verify the pipeline activity at the time of sampling.
2.3.7 Vapor Pressure Samples Samples that are to be tested for volatility (vapor pressure, Rvp) require special handling. The most common type of sample is a running sample; however, spot samples can be taken. Under no circumstances is it allowable to decant a vapor pressure sample from one container to another. The sample must be taken in the container that it will be stored in. Vapor pressure samples are usually taken in glass bottles using a cage sampler or a lead weight and a cord. Spot samples will be full when pulled from the liquid. Quickly pour out approximately 20% of the liquid, cap the bottle and invert it. It is common practice to place inverted vapor pressure samples in ice, which is carried in a cooler. It is possible to use metal cans, provided that the sample is taken in the can and the cap makes a vapor tight seal. Plastic bottles are not permitted.
Hatch
6”
Top sample Upper sample
Upper third
Middle sample
Middle third
Lower sample Outlet sample
Lower third
Outlet
2.3.4 Composite Spot Samples Upper, middle, and lower samples are combined in equal proportions in the field to make a composite spot sample. Other types of composites, such as vessel composites, are not made in the field because the component percentages cannot be accurately measured under field conditions. These composites are made in the laboratory.
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