Test Method for Density of Liquefied Petroleum Gas

Test Method for Density of Liquefied Petroleum Gas

Liquefied Petroleum Gas (LPG) is a by product of petroleum refining and natural gas extraction. It is gaseous under normal temperature and atmospheric pressure. When moderate pressure is applied, it turns into liquid with its volume greatly reduced (approximately 1/250 of the gaseous state), which facilitates storage and transportation in steel cylinders or tanks. Its main components are propane and butane, together with small amounts of propylene and butylene. Pure LPG is colourless and odourless. For safety purposes, ethyl mercaptan is artificially added so that odour can be detected in case of leakage for risk identification.

Test Objectives

1.Determine the density (or relative density) of LPG at the specified temperature to evaluate product composition (proportion of propane and butane).

2.Serve as a quality indicator to verify whether LPG complies with relevant product standards for incoming quality acceptance and factory inspection.

3.Support material metering conversion: density is the fundamental parameter for mass volume conversion, applied to tank farm metering and custody transfer in commercial transactions.

4.Assist in estimating physical chemical properties such as vaporization performance and calorific value, providing reference for storage, transportation and safe operation.

5.Distinguish LPG from different batches and monitor the stability of production and blending processes.

Test Sample and Apparatus

Test sample: Liquefied Petroleum Gas (LPG)

Test instrument: SH0221 Liquefied Petroleum Gas Density Tester, compliant with ASTM D1657.

Test Procedures

1.Instrument Preparation Check the tightness of the pressure density cylinder, pressure resistant hydrometer and constant temperature water bath. Ensure no leakage or damage and that the temperature control system works properly.

2.Sample Rinsing Rinse the pressure test cylinder thoroughly 2-3 times with a small quantity of test LPG sample to remove air and residual contaminants inside the cylinder and prevent accuracy deviation.

3.Sample Filling Continuously feed LPG sample to fully fill the pressure cylinder without internal air bubbles, so that the built in hydrometer can float freely, then seal the cylinder.

4.Thermal Equilibration Place the pressure cylinder into a constant temperature water bath set at 20 ℃ (standard reference temperature). Keep it stationary until the sample temperature is fully stabilized without fluctuation.

5.Reading Observation After the hydrometer and liquid surface become stable, record the original scale reading of the hydrometer as well as the actual measured sample temperature.

6.Data Correction Perform corrections in accordance with ASTM D1250 / API MPMS 11.1: correct meniscus error, glass thermal expansion error and temperature deviation, and convert the result to standard density at 20 ℃.

7.Post test Work Release pressure and drain the sample. Clean the equipment and organize test data.

Test Result

The measured density of the LPG sample falls within the typical range for commercial liquefied petroleum gas (0.50～0.58 g/cm³). The physical chemical indicators of the sample are qualified.