ASTM D8236-18

Standard Practice for Preparing an Equilibrium Liquid/Vapor Sample of Live Crude Oil, Condensates, or Liquid Petroleum Products Using a Manual Piston Cylinder for Subsequent Liquid Analysis or Gas Analysis

SIGNIFICANCE AND USE
5.1 This practice allows for compositional analysis of the gases in equilibrium with crude oil, condensate, and liquid petroleum products at a 4:1 vapor/liquid ratio at ambient temperature for analysis using typical instrumentation (RGA) already available in typical refinery laboratories. These highly volatile components can result in vapor pressure conditions above atmospheric pressure, so this mechanically simple system is easily adaptable to day-to-day application at low cost/effort using existing analytical equipment.  
5.2 This practice allows for compositional analysis and day-to-day tracking or trending of the light hydrocarbons in crude oil for the purpose of identifying unusual blending of NGL, LPG, butane etc. into individual crude oil batch receipts.  
5.3 This practice allows identification of gases: including: CO, CO2, H2, H2S, N2, O2, CH4, C2H6, C3H8, etc. that can contribute to vapor pressure by Test Method D6377, but are not identified using Test Method D8003 (see Note 1). These components can originate from production or can be the result of the use of pad gas and may not be native to the original product. Significant difference in Test Method D6377 vapor pressure measurements at low V/L (for example, 0.1:1) versus high V/L (for example, 4:1) indicate the contribution of high vapor pressure gases such as those in 5.2.
Note 1: Test Method D8003 does identify: CH4, C2H6, and C3H8. Test Method D8003 does not identify: CO, CO2, H2, H2S, N2, and O2.  
5.4 Nitrogen and combustion gases (mostly nitrogen and CO2 with minor concentrations of air) at positive pressures up to 2500 mm water column (nominal 4 psig) is required by International Marine Organization (IMO) Marine Pollution (MARPOL) and Safety of Life at Sea (SOLAS) regulations for the marine transport of crude oil. Analysis of the equilibrium vapor may be required to determine the contribution of inert gases to the total vapor pressure of the crude oil on receipt at the discharge port or refine...
SCOPE
1.1 This practice covers the preparation of an equilibrium gas sample of live crude oil, condensate, or liquid petroleum products, using a Practice D8009 manual piston cylinder (MPC) as a vapor tight expansion chamber to generate an equilibrium vapor/liquid pair at a known temperature and vapor/liquid ratio (V/L). Inert gas such as helium or argon is injected to the equilibrium vapor space of the MPC to provide an equilibrium vapor sample sufficiently above atmospheric pressure for subsequent analysis using a standard refinery gas analyzer (RGA) such as described in Test Method D7833. Other gas analysis methods may be used provided they meet the minimum performance criteria stated in 7.4.1.  
1.2 This practice is suitable for UN Class 3 Liquid samples having vapor pressures between 0 kPa and 300 kPa at 50.0 °C, and 0.1:1 to 4:1 vapor/liquid ratio, spanning the nominal range near bubble point (Test Method D6377 VPCr,0.1) to Test Methods D323 (RVP), D4953, and D5191 (V/L=4). The temperature may vary over a wide range, provided that the cylinder is maintained at isothermal and isobaric conditions to prevent condensation of equilibrium vapor upon cooling either in the cylinder or in the injection system of the Refinery Gas Analyzer (RGA, Test Method D7833). The method is best suited for preparation of an equilibrium gas/liquid pair near ambient conditions, typical of routine daily operations in a typical refinery quality assurance or marine terminal laboratory, to routinely monitor the light ends content of crude oil receipts.  
1.3 This practice is suitable to prepare an equilibrium liquid/vapor sample pair in a sealed sampling system (no light ends loss from either phase). The equilibrium gas phase is suitable for subsequent gas analysis of both hydrocarbon and fixed/inert gases in the sample, including: hydrogen, oxygen, nitrogen, carbon dioxide, carbon monoxide, hydrogen sulfide, C1 to C7 hydrocarbons at levels consist...

General Information

• Status: Published
• Publication Date: 14-Dec-2018
• ICS: 75.080 - Petroleum products in general
• Technical Committee: D02 - Petroleum Products, Liquid Fuels, and Lubricants
• Drafting Committee: D02.08 - Volatility

Relations

• Refers: ASTM D4953-20 - Standard Test Method for Vapor Pressure of Gasoline and Gasoline-Oxygenate Blends (Dry Method)
• Effective Date: 01-May-2020
• Refers: ASTM D5191-18a - Standard Test Method for Vapor Pressure of Petroleum Products and Liquid Fuels (Mini Method)
• Effective Date: 01-Dec-2018
• Refers: ASTM D6377-15 - Standard Test Method for Determination of Vapor Pressure of Crude Oil: VPCR<inf>x</inf >&#x2009;(Expansion Method)
• Effective Date: 01-Oct-2015
• Refers: ASTM D8003-15 - Standard Test Method for Determination of Light Hydrocarbons and Cut Point Intervals in Live Crude Oils and Condensates by Gas Chromatography
• Effective Date: 01-Jun-2015
• Refers: ASTM D323-15 - Standard Test Method for Vapor Pressure of Petroleum Products (Reid Method)
• Effective Date: 01-Apr-2015
• Refers: ASTM D6377-14 - Standard Test Method for Determination of Vapor Pressure of Crude Oil: VPCR<inf>x</inf >&#8201;&#40;Expansion Method&#41;
• Effective Date: 01-Oct-2014
• Refers: ASTM D5191-13 - Standard Test Method for Vapor Pressure of Petroleum Products (Mini Method)
• Effective Date: 01-Dec-2013
• Refers: ASTM D7833-12 - Standard Test Method for Determination of Hydrocarbons and Non-Hydrocarbon Gases in Gaseous Mixtures by Gas Chromatography
• Effective Date: 01-Nov-2012
• Refers: ASTM D4953-06(2012) - Standard Test Method for Vapor Pressure of Gasoline and Gasoline-Oxygenate Blends (Dry Method)
• Effective Date: 01-Nov-2012
• Refers: ASTM D5191-12 - Standard Test Method for Vapor Pressure of Petroleum Products (Mini Method)
• Effective Date: 01-Sep-2012
• Refers: ASTM D4057-06(2011) - Standard Practice for Manual Sampling of Petroleum and Petroleum Products
• Effective Date: 01-Jun-2011
• Refers: ASTM D6377-10 - Standard Test Method for Determination of Vapor Pressure of Crude Oil: VPCR_x (Expansion Method)
• Effective Date: 01-Oct-2010
• Refers: ASTM D5191-10a - Standard Test Method for Vapor Pressure of Petroleum Products (Mini Method)
• Effective Date: 01-Jul-2010
• Refers: ASTM D5191-10 - Standard Test Method for Vapor Pressure of Petroleum Products (Mini Method)
• Effective Date: 01-May-2010
• Refers: ASTM D6377-08 - Standard Test Method for Determination of Vapor Pressure of Crude Oil: VPCR_x (Expansion Method)
• Effective Date: 01-Jul-2008

Overview

ASTM D8236-18 is the internationally recognized standard practice for preparing equilibrium liquid/vapor samples of live crude oil, condensates, or liquid petroleum products using a manual piston cylinder. This method enables subsequent compositional analysis of both gas and liquid phases, supporting a range of day-to-day operational needs in refinery and marine terminal laboratories. It is primarily aimed at obtaining reproducible equilibrium samples for gas analysis (commonly by Refinery Gas Analyzer - RGA) or liquid analysis, while preserving the integrity of volatile and light hydrocarbons under controlled vapor/liquid ratios and near-ambient conditions.

The standard facilitates accurate assessment of equilibrium vapor composition in volatile petroleum products, aligning with regulatory and quality assurance requirements for handling bulk petroleum samples.

Key Topics

• Equilibrium Sample Preparation: Procedures to generate and preserve equilibrium vapor/liquid pairs at specified vapor/liquid (V/L) ratios, minimizing loss or alteration of light hydrocarbons and dissolved gases.
• Use of Manual Piston Cylinder (MPC): Guidelines for employing manual piston cylinders (as detailed in ASTM D8009) as vapor-tight, pressurized sample containers, with inert gas (e.g., helium or argon) injection to achieve positive vapor pressure.
• Compositional Gas Analysis: Methods to analyze equilibrium vapors for hydrocarbons (C₁–C₇), inert gases (e.g., nitrogen, carbon dioxide), hydrogen, oxygen, hydrogen sulfide, and others using industry-standard RGAs and gas chromatography.
• Suitability for Multiple Petroleum Products: Applicable to live and dead crude oils, condensates, and various UN Class 3 liquids with vapor pressures between 0–300 kPa at 50°C.
• Sample Integrity and Quality Control: Best practices for sample collection, cylinder handling, and contamination prevention to ensure representative and reliable test results.
• Regulatory Relevance: Compliance support for international marine transport regulations, such as IMO's MARPOL and SOLAS, where monitoring of inert and combustion gases is needed.

Applications

ASTM D8236-18 provides significant practical value in the following areas:

• Refinery Laboratory Operations: Routine quality assurance, trending, and batch-to-batch consistency checks of incoming crude oils and condensates.
• Marine Terminal Compliance: Evaluation of inert gas and vapor pressure conditions for marine shipments, aiding in compliance with international safety (SOLAS) and pollution (MARPOL) regulations.
• Compositional Assessment: Identification and monitoring of light hydrocarbon blending (NGL, LPG, butane) or contamination in crude oil receipts.
• Track Volatile Components: Day-to-day tracking of volatiles, including non-native components from production or pad gas usage, by measuring equilibrium vapor composition.
• Support Standard Analytical Methods: Ensures compatibility with widely used refinery gas analyzers (RGA) and is harmonized with related ASTM test methods (e.g., D6377, D8003, D323).

Related Standards

ASTM D8236-18 references and complements several related industry standards, including:

• ASTM D8009: Practice for Manual Piston Cylinder Sampling for Volatile Crude Oils, Condensates, and Liquid Petroleum Products.
• ASTM D6377: Test Method for Vapor Pressure of Crude Oil (VPCR, Expansion Method).
• ASTM D8003: Test Method for Determination of Light Hydrocarbons in Live Crude Oils by Gas Chromatography.
• ASTM D7833: Test Method for Determination of Hydrocarbons and Non-Hydrocarbon Gases in Gaseous Mixtures by Gas Chromatography.
• ASTM D323, D4953, D5191: Various vapor pressure test methods for petroleum products.
• ASTM D4057: Practice for Manual Sampling of Petroleum and Petroleum Products.

By using ASTM D8236-18, laboratories and operations ensure sample integrity, optimize compositional vapor/liquid analysis, and meet critical industry and regulatory requirements for live crude oil and liquid petroleum products. This standardized approach enhances reliability, comparability, and safety in the volatile hydrocarbon measurement process.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D8236 − 18
Standard Practice for
Preparing an Equilibrium Liquid/Vapor Sample of Live Crude
Oil, Condensates, or Liquid Petroleum Products Using a
Manual Piston Cylinder for Subsequent Liquid Analysis or
Gas Analysis
This standard is issued under the fixed designation D8236; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope nitrogen, carbon dioxide, carbon monoxide, hydrogen sulfide,
C1 to C7 hydrocarbons at levels consistent with the Test
1.1 This practice covers the preparation of an equilibrium
Method D7833 method used. The equilibrium liquid phase can
gas sample of live crude oil, condensate, or liquid petroleum
be subsequently analyzed by Test Method D8003 to obtain
products, using a Practice D8009 manual piston cylinder
paired analytical results on both the equilibrium liquid and
(MPC) as a vapor tight expansion chamber to generate an
vapor pair with a sealed sample system.
equilibrium vapor/liquid pair at a known temperature and
vapor/liquid ratio (V/L). Inert gas such as helium or argon is
1.4 Addition of the diluent gas provides a positive pressure
injected to the equilibrium vapor space of the MPC to provide
sample to allow the use of a typical RGA-type gas injection
an equilibrium vapor sample sufficiently above atmospheric
system that operates only slightly above barometric pressure.
pressure for subsequent analysis using a standard refinery gas
The preferred diluent gas shall be the same as the carrier gas
analyzer (RGA) such as described in Test Method D7833.
used in the RGA(typically helium or argon). Choice of diluent
Other gas analysis methods may be used provided they meet
or carrier gas may affect the ability to detect some inert gases
the minimum performance criteria stated in 7.4.1.
(especially O or H ) in some RGAconfigurations conforming
2 2
1.2 This practice is suitable for UN Class 3 Liquid samples
to Test Method D7833.
having vapor pressures between 0 kPa and 300 kPa at 50.0 °C,
1.5 The VLE gas generation and subsequent RGAoutput is
and 0.1:1 to 4:1 vapor/liquid ratio, spanning the nominal range
usedasascreeningmethodtoidentifygascomponentsthatcan
near bubble point (Test Method D6377 VPCr,0.1) to Test
be present in the crude oil affecting the total vapor pressure.
Methods D323 (RVP), D4953, and D5191 (V/L=4). The
The RGA output only represents the equilibrium vapor com-
temperature may vary over a wide range, provided that the
ponents present and relative to one another. Due to dilution of
cylinder is maintained at isothermal and isobaric conditions to
the VLE gas with inert gas, the RGA output does not purport
prevent condensation of equilibrium vapor upon cooling either
to accurately provide the actual vapor composition at VLE
in the cylinder or in the injection system of the Refinery Gas
Analyzer (RGA, Test Method D7833). The method is best conditions and is definitely not representative of the composi-
tion of the whole sample.
suited for preparation of an equilibrium gas/liquid pair near
ambient conditions, typical of routine daily operations in a
1.6 The values stated in SI units are to be regarded as
typical refinery quality assurance or marine terminal
standard. The values given in parentheses after SI units are
laboratory, to routinely monitor the light ends content of crude
provided for information only and are not considered standard.
oil receipts.
1.7 This standard does not purport to address all of the
1.3 This practice is suitable to prepare an equilibrium
safety concerns, if any, associated with its use. It is the
liquid/vapor sample pair in a sealed sampling system (no light
responsibility of the user of this standard to establish appro-
ends loss from either phase). The equilibrium gas phase is
priate safety, health, and environmental practices and deter-
suitable for subsequent gas analysis of both hydrocarbon and
mine the applicability of regulatory limitations prior to use.
fixed/inert gases in the sample, including: hydrogen, oxygen,
1.8 This international standard was developed in accor-
dance with internationally recognized principles on standard-
This practice is under the jurisdiction ofASTM Committee D02 on Petroleum
ization established in the Decision on Principles for the
Products, Liquid Fuels, and Lubricants and is the direct responsibility of Subcom-
Development of International Standards, Guides and Recom-
mittee D02.08 on Volatility.
mendations issued by the World Trade Organization Technical
Current edition approved Dec. 15, 2018. Published February 2019. DOI:
10.1520/D8236-18. Barriers to Trade (TBT) Committee.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D8236 − 18
2. Referenced Documents open sample containers, such as cans, bottles, and other
2 atmospheric containers.
2.1 ASTM Standards:
3.1.3.2 Discussion—Samplesandbulkstorage(tank)liquids
D323 TestMethodforVaporPressureofPetroleumProducts
mayormaynotappeartoboilvisibly(rolling)butvaporization
(Reid Method)
(off-gassing) is occurring.
D4057 Practice for Manual Sampling of Petroleum and
3.1.4 manual piston cylinder (MPC), n—a Practice D8009
Petroleum Products
vapor and liquid tight (“sealed”) pressurized sample cylinder
D4953 Test Method for Vapor Pressure of Gasoline and
container with an internal piston that effectively divides the
Gasoline-Oxygenate Blends (Dry Method)
container into two separate compartments and that is attached
D5191 Test Method for Vapor Pressure of Petroleum Prod-
to a rod which allows the user to manually move the piston in
ucts and Liquid Fuels (Mini Method)
order to collect volatile liquid samples at low sample point
D6377 Test Method for Determination of Vapor Pressure of
pressures.
Crude Oil: VPCR (Expansion Method)
x
D7833 Test Method for Determination of Hydrocarbons and
3.1.5 single-phase fluid, n—afluid(liquidorgas)thathasno
Non-Hydrocarbon Gases in Gaseous Mixtures by Gas
separate vapor and liquid phases.
Chromatography
3.1.6 vapor liquid ratio, n—the volume of the vapor space
D7975 Test Method for Determination of Vapor Pressure of
formed above a liquid sample in a piston sampling cylinder or
Crude Oil: VPCR -F(Tm°C) (Manual Expansion Field
x
test apparatus divided by the original sample volume (not
Method)
corrected for the small volume change associated with gener-
D8003 Test Method for Determination of Light Hydrocar-
ating the vapor phase).
bons and Cut Point Intervals in Live Crude Oils and
3.2 Definitions of Terms Specific to This Standard:
Condensates by Gas Chromatography
3.2.1 combustion gas, n—gas generated as a result of
D8009 Practice for Manual Piston Cylinder Sampling for
hydrocarbon combustion.
Volatile Crude Oils, Condensates, and Liquid Petroleum
3.2.1.1 Discussion—Commonlyusedaspadgasintankship
Products
cargo tanks.
3. Terminology
3.2.2 isobaric, adj—having a constant pressure throughout.
3.2.3 isothermal, adj—having a constant temperature
3.1 Definitions:
3.1.1 dead crude oil, n—crude oil with sufficiently low throughout.
vapor pressure that, when exposed to normal atmospheric
3.2.4 pad gas, n—gas used to prevent the ingress of atmo-
pressure at room temperature, does not result in boiling of the
spheric gases (predominately O,N ) into a tank, or storage
2 2
sample.
container/vesselaswellaspreventexplosivegasmixturesfrom
3.1.1.1 Discussion—These crudes will have vapor pressures
forming in the vapor space above a flammable liquid, or a gas
below atmospheric pressure at room temperature.
used to pressurize a tank temporarily to facilitate a liquid
3.1.1.2 Discussion—A crude oil is normally considered
transfer or maintain pump suction pressure.
“live” until the vapor pressure can be established using Test
3.2.4.1 Discussion—Commonly used pad gases include but
Method D6377 or D7975. Sampling and handling of dead
are not limited to: nitrogen, carbon dioxide, and methane.
crude oils can usually be performed without concern in open,
3.3 Abbreviations:
non-pressurized sample containers, such as cans, bottles, and
3.3.1 CV—charge valve
other atmospheric containers as described in Practice D4057.
3.3.2 FPC—floating piston cylinder
3.1.2 dead volume, n—the dead volume includes any inci-
3.3.3 MPC—manual piston cylinder
dental volume from fittings, valves, threaded port connections,
the annular volume around the piston, channel volume within
3.3.4 psia—pounds per square inch absolute (psia = psig +
the end caps, and volume within the pressure relief device and
barometric pressure)
valvesthatcanaffecttheactualV/LversusV/Lcalculatedfrom
3.3.5 psig—pounds per square inch gauge (psig = psia –
thelineardisplacementofthecylinderrodusedtocalculatethe
barometric pressure)
volume of the cylindrical sample chamber.
3.3.6 PRV—pressure relief valve
3.1.3 live crude oil, n—crudeoilwithsufficientlyhighvapor
3.3.7 PV—purge valve
pressure that it would boil if exposed to normal atmospheric
3.3.8 RGA—refinery gas analyzer
pressure at room temperature.
3.1.3.1 Discussion—Sampling and handling of samples of
3.3.9 SV—sample valve
live crude oils will necessitate the use of the closed sample
3.3.10 VLE—vapor-liquid equilibrium
container to maintain sample integrity and preclude the use of
3.3.11 V/L—vapor/liquid volume ratio
4. Summary of Practice
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
4.1 A live crude oil or condensate sample is obtained using
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
an MPC, as described in Practice D8009, to avoid loss of any
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. light hydrocarbon or dissolved gases. After any other desired
D8236 − 18
tests are completed, the remaining single-phase sample volume 5. Significance and Use
within the MPC is reduced to 20 % of MPC volume by
5.1 This practice allows for compositional analysis of the
iso-barically purging the excess sample. The piston is then
gases in equilibrium with crude oil, condensate, and liquid
extended to 100 % by injecting an inert gas such as helium or
petroleum products at a 4:1 vapor/liquid ratio at ambient
argon, at nominally 200 kPa (14.3 psig), creating a 4:1
temperature for analysis using typical instrumentation (RGA)
vapor/liquid ratio.
already available in typical refinery laboratories. These highly
volatile components can result in vapor pressure conditions
4.2 Other V/Ls or inert gas pressures can be used, but
above atmospheric pressure, so this mechanically simple sys-
V/L=4 and 200 kPa will ensure that the majority of the
tem is easily adaptable to day-to-day application at low
dissolved gases such as oxygen, nitrogen, and CO will be in
cost/effort using existing analytical equipment.
thevaporphaseatsufficientlylowpressurethatthesystemwill
behave ideally, and that a sufficient volume of vapor is
5.2 This practice allows for compositional analysis and
available to properly flush the GC inlet system, and that the
day-to-day tracking or trending of the light hydrocarbons in
liquid will not release or absorb large quantities of gas with
crude oil for the purpose of identifying unusual blending of
minor variations of temperature or pressure.
NGL, LPG, butane etc. into individual crude oil batch receipts.
4.3 The cylinder is agitated for 2 min to ensure a close
5.3 This practice allows identification of gases: including:
approach to equilibrium.
CO, CO,H,H S, N,O,CH,C H,C H , etc. that can
2 2 2 2 2 4 2 6 3 8
contributetovaporpressurebyTestMethodD6377,butarenot
4.4 After the equilibration period the cylinder is oriented
identified using Test Method D8003 (see Note 1). These
vertically vapor side up and sample valve connection point to
components can originate from production or can be the result
the sample chamber at the highest point, to allow the liquid to
of the use of pad gas and may not be native to the original
settle to the bottom of the sample chamber. The equilibrium
product. Significant difference in Test Method D6377 vapor
vapor phase is then transferred to a refinery gas analyzer to
pressure measurements at low V/L (for example, 0.1:1) versus
determine the equilibrium gas composition.
high V/L (for example, 4:1) indicate the contribution of high
4.4.1 This practice is intended for use in screening the bulk
vapor pressure gases such as those in 5.2.
of gaseous components present in the equilibrium vapor. This
NOTE1—TestMethodD8003 doesidentify:CH ,C H ,andC H .Test
4 2 6 3 8
practice is not intended to measure or report trace quantities
Method D8003 does not identify: CO, CO,H,H S, N , and O .
2 2 2 2 2
(<0.1 % by mass) although some RGAtest methods may have
5.4 Nitrogen and combustion gases (mostly nitrogen and
lower quantitation limits for some or all components listed.
CO with minor concentrations of air) at positive pressures up
4.5 After transferring and testing the vapor phase with the
to 2500 mm water column (nominal 4 psig) is required by
RGA the cylinder may be oriented with the sampling valve
International Marine Organization (IMO) Marine Pollution
facing vertically downward to obtain an equilibrium liquid
(MARPOL) and Safety of Life at Sea (SOLAS) regulations for
sample for other analysis not included in this practice.
the marine transport of crude oil. Analysis of the equilibrium
vapor may be required to determine the contribution of inert
4.6 Isobaric operation during sample withdrawal can be
gases to the total vapor pressure of the crude oil on receipt at
obtained by applying a constant pressure to the handle (pre-
the discharge port or refinery.
charge) side of the MPC. The pre-charge side of the cylinder
may also be pressurized with inert gas if the user is unable to
6. Interferences
put sufficient force on the piston handle to maintain the
pressure.
6.1 Interference in a sampling procedure is anything that
4.6.1 For Test Method D8003 or other similar methods, the compromises the integrity of the sample.
liquid phase must be transferred into a separate small cylinder
6.2 Incorrect choice of a sample point location can result in
that meets the minimum 300 psig injection pressure require-
a non-representative sample due to solid or liquid
ments forTest Method D8003, or an inert gas sampling bag for
contaminants, separate phases, storage tank stratification, etc.
gaseous GC injection, provided that all connections are evacu-
6.3 Reactivity of steel surfaces can result in the chemical
ated prior to transfer.
alteration of trace reactive components such as H S, COS, and
4.6.2 It is recommended that for direct connection of the
mercaptans.
MPC to the RGA, vapor transfers be through a small glass
impinge (liquid knock-out) or coil of small internal diameter
6.4 A lubricant, used on the piston or other internal wetted
PTFE tubing, or combination thereof, so that any inadvertent
parts, that is soluble in hydrocarbon can contaminate the
entrainment of crude oil liquid is visible to the operator
sample and analytical equipment.
sufficiently quickly that the sample loop flow can be stopped
6.5 Leakage can result in loss of sample. Consult the
before the RGA inlet is contaminated by liquid crude oil. All
manufacturer’s guidelines for suitable procedures to verify a
transfer lines must be evacuated or sufficiently flushed to
leak-free cylinder, such as vacuum or pressure testing.
ensure that a representative sample is injected into the GC.
4.6.3 It is recommended that the 20 % cylinder rod spacer 6.6 Failure to flush sample lines and dead volumes can
be put in place during vapor transfers from the cylinder as an
result in contaminated and non-representative samples that
additional precaution against inadvertent liquid crude transfer. cause a high bias when vapor pressure is measured at V/L< 1.
D8236 − 18
6.7 Fully air-saturated samples will report barometric pres- the piston rod diameter plus the material thickness. For
sure at the time at V/L approaching 0. example: an 80 % guide length is based on 80 % of the length
of the piston stroke.Acylinder with a 20.3 cm (nominal 8 in.)
6.8 Sampling from stratified tanks, dead zones in flowing
piston stroke length will have a maximum 16.2 cm (nominal
systems, or inappropriate time periods can result in non-
6.4 in.) length guide.
representative samples.
7.1.3.2 Volumetric guides for 20 %, 40 %, and 100 % are
6.9 Any material that can create carryover contamination
required for this test method.
from one sample to the next shall be removed from the
7.1.3.3 Manual piston cylinders that are not equipped with a
cylinder, and the cylinder thoroughly cleaned before collection
piston position indicator shall not be used.
of subsequent samples. In addition to cleaning the interior
7.2 Transfer lines, valves, pressure gauges and related
metal surfaces and cleaning the soft parts (O-rings, for
equipment in the transfer system shall be corrosion resistant
example), consideration should be given to replacing the soft
(typically stainless steel) and designed consistent with maxi-
parts if they might have absorbed any contamination. Ex-
mum anticipated pressure. The equilibrium gas transfer lines
amples of contaminants include glycol, amine, lubricants,
should be as short as practical to prevent contamination with
sulfur species, solvents, methanol, etc.
atmospheric air by preventing appropriate equilibrium gas
7. Apparatus purging or evacuation prior to analysis.
NOTE 2—While not required by this practice, the use of non-reactive
7.1 Manual Piston Cylinder (MPC) as described in Practice
and non-absorptive materials is recommended, especially when sampling
D8009:
to determine trace levels of reactive or polar materials such as H S and
7.1.1 Construction, typically fabricated from corrosion-
water.
resistant material such as 316 stainless steel or aluminum.
7.3 Vapor transfer line 3.175 mm ( ⁄8 in.) PTFE (Teflon™)
Protective internal coatings or surface treatments are accept-
translucent tubing or equivalent with a pressure rating exceed-
able provided that they do not adversely affect the free
ing 400 kPa, or glass impinger type liquid trap with sufficient
movement of the piston, or effectiveness of the seals (see Fig.
pressureratingfortheGCinletsystem,orcombinationthereof.
1).
7.4 Refinery Gas Analyzer.
7.1.2 The cylinder shall have provision for moving the
7.4.
...