ASTM D3700-16,Standard Practice for Obtaining LPG Samples Using a Floating Piston Cylinder.
ASTM D3700-16 covers the equipment and procedures for obtaining a representative sample of liquefied petroleum gas (LPG), such as specified in ASTM Specification D1835, GPA 2140, and comparable international standards. It may also be used for other natural gas liquid (NGL) products that are normally single phase (for example, NGL mix, field butane, and so forth), defined in other industry specifications or contractual agreements, and for volatile (higher vapor pressure) crude oils.
ASTM D3700-16 allows the collection of a representative sample of LPG that may contain trace volatile dissolved components such as methane, ethane, and nitrogen.
4. Summary of Practice
4.1 A liquid petroleum gas (LPG) sample is transferred as aliquid under pressure from a sample point to a floating piston cylinder. The floating piston cylinder (FPC) is designed tocollect liquid samples with no vaporization by displacing apiston against a pressurizing fluid (preferably an inert gas ).The piston serves as a physical barrier between the sample and the pressurizing fluid, at the sampling pressure. The position of the piston at the end of sampling indicates the percent fill of the sample cylinder.
4. 2 It is the responsibility of the user of this practice to locate the sample point at a suitable location and orientation where the product being sampled is a representative, singlphase, homogeneous liquid.
6. interferences
6. 1 An interference in a sampling procedure is anything which compromises the integrity of the sample
6.2 Incorrect choice of a sample point location can result ina non-representative sample due to solid or liquid contaminants, two phases, storage tank stratification, and so forth.
6.3 Reactivity of steel surfaces can remove or chemically alter trace reactive components such as H2S, COS, and mercaptan.
6. 4 A lubricant used on the floating piston or other intenal wetted parts that is soluble in LPG can contaminate the sample.