Standard Test Method for Vapor Pressure of Petroleum Products (Mini Method)

ASTM D5191 covers the use of automated vapor pressure instruments to determine the total vapor pressure exerted in vacuum by air-containing, volatile, liquid petroleum products, including automotive spark-ignition fuels with or without oxygenates. This test method is suitable for testing samples with boiling points above 0 °C (32 °F) that exert a vapor pressure between 7 kPa and 130 kPa (1.0 psi and 18.6 psi) at 37.8 °C (100 °F) at a vapor-to-liquid ratio of 4:1.

Measurements are made on liquid sample sizes in the range from 1 mL to 10 mL. No account is made for dissolved water in the sample.

D5191 is an automated mini test method for the automated determination of Dry Vapor Pressure Equivalent (DVPE) often called Reid Vapor Pressure (RVP) and the Total Vapor Pressure of hydrocarbon blends and fuels.

D5191 was developed to improve the poor precision, long run times and large amount of sample required in manual methods.

Eralytics has designed Eravap a triple expansion tester that offers significant advantages in performance an ease of use than similar instruments in the market. The Eravap Software is self-intuitive and the method configuration is user friendly requiring just a few steps for the method set up. Eravap possesses a special software that allows to monitor the instruments in the field during at line operations and easy transfer of data to coordinating labs and users. It conforms to other standard test methods like D4953, IP394 and EN 13016-1                                                                                                                       

Referenced Documents

ASTM Standards:

D2892 Test Method for Distillation of Crude Petroleum (15-Theoretical Plate Column)
D4057 Practice for Manual Sampling of Petroleum and Petroleum Products
D4953 Test Method for Vapor Pressure of Gasoline and Gasoline-Oxygenate Blends (Dry Method)
D5798 Specification for Ethanol Fuel Blends for Flexible-Fuel Automotive Spark-Ignition Engines
D6299 Practice for Applying Statistical Quality Assurance and Control Charting Techniques to Evaluate Analytical Measurement System Performance
D6377 Test Method for Determination of Vapor Pressure of Crude Oil: VPCRx (Expansion Method)
D6378 Test Method for Determination of Vapor Pressure (VPX) of Petroleum Products, Hydrocarbons, and Hydrocarbon-Oxygenate Mixtures (Triple Expansion Method)
D7717 Practice for Preparing Volumetric Blends of Denatured Fuel Ethanol and Gasoline Blendstocks for Laboratory Analysis

2.2 IP Standard:
IP 481 Test Method for Determination of the Air Saturated Vapour Pressure (ASVP) of Crude Oil4

Summary of Test Method

A known volume of chilled, air-saturated sample is introduced into a thermostatically controlled, evacuated test chamber, or a test chamber with a moveable piston that expands the volume after sample introduction, the internal volume of which is five times that of the total test specimen introduced into the chamber. After introduction into the test chamber, the test specimen is allowed to reach thermal equilibrium at the test temperature, 37.8 °C (100 °F). The resulting rise in pressure in the chamber is measured using a pressure transducer sensor and indicator. Only total pressure measurements (sum of the partial pressure of the sample and the partial pressure of the dissolved air) are used in this test method, although some instruments can measure the absolute pressure of the sample as well.

Significance and Use

 Reid vapor pressure is a very important physical property of volatile liquids. The vapor pressure of gasoline and gasoline-oxygenate blends is regulated by various government agencies.

Specifications for volatile petroleum products generally include vapor pressure limits to ensure products of suitable volatility performance.

The ASTM D5191 method is more precise than Test Method D4953, uses a small sample size (1 mL to 10 mL), and requires about 7 min to complete the test.

After preparing and calibrating the apparatus according to manufacturer’s instructions, the system’s performance is verified to comply with tables 1 and 2 below.

Procedure

Remove the sample from the cooling bath or refrigerator, dry the exterior of the container with absorbent material, uncap, and insert a transfer tube or chilled syringe. Draw a bubble-free aliquot of sample into a gas tight syringe or transfer tube and deliver this test specimen to the test chamber as rapidly as possible. The total time between opening the chilled sample container and inserting/securing the syringe into the sealed test chamber shall not exceed 1 min.

Follow the manufacturer’s instructions for introduction of the test specimen into the test chamber, and for operation of the instrument to obtain a total vapor pressure result for the test specimen.

Set the instrument to read the result in terms of total vapor pressure. If the instrument is capable of calculating a dry vapor pressure equivalent value (DVPE), make sure that only the parameters in 14.2 are used.

Calculation

Record the total vapor pressure reading from the instrument to the nearest 0.1 kPa (0.01 psi). For instruments that do not automatically record a stable pressure value, manually record the pressure indicator reading every minute to the nearest 0.1 kPa. When three successive readings agree to within 0.1 kPa, record the result to the nearest 0.1 kPa

(0.01 psi).

14.2 Calculate the DVPE using Eq 1. Ensure that the instrument reading used in this equation corresponds to the

total pressure and has not been corrected by an automatically programmed correction factor:

DVPE, kPa(psi) = (0.965 X) –  A    (1)

where:

X = measured total vapor pressure in kPa (psi), and

A = 3.78 kPa (or 0.548 psi).

NOTE 14—The correlation equation was derived from the results of the 1988 cooperative program 8 and confirmed in the 1991 interlaboratory study.9

14.3 The calculation described by Eq 1 can be accomplished automatically by the instrument, if so equipped, and in such cases the user shall not apply any further corrections.

Report

Report the DVPE value to the nearest 0.1 kPa (0.01 psi) without reference to temperature, along with the volume container size (250 mL or 1 L) in which the result was obtained.

If the sample was observed to be hazy in, report the test result followed by the letter H.

NOTE —The precision and bias statements have not been determined for hazy samples since these types of samples have not been evaluated as part of an interlaboratory study.

NOTE —The inclusion of the letter H in the results is intended to alert the data recipient that the sample analyzed was hazy. In the event that a laboratory has a computer system that is incapable of reporting alphanumeric results in accordance with the requirements, it is permissible for the laboratory to report the result obtained, along with a statement or annotation that clearly conveys to the data recipient that the analyzed sample was hazy.