ASTM D4057 standard practice for manual sampling of petroleum and petroleum products
6. Apparatus
6.1 General Sample Container Design Considerations:
6.1.1 Sample containers come in a variety of shapes, sizes, and materials. Select the proper container based on the product to be sampled to ensure that there will be no interaction between the product sampled and the container that would affect the integrity of either. The following are general design considerations for sample containers:
6.1.1.1 No internal pockets or dead spots;

6.1.1.2 Internal surfaces designed to minimize corrosion, encrustation, and water/sediment clingage;

6.1.1.3 An inspection cover/closure of sufficient size to facilitate filling, inspection, and cleaning;

6.1.1.4 Designed to allow the preparation, and transfer to the analytical apparatus, of a homogeneous mixture of the sample while minimizing the loss of any constituents that affect the representativeness of the sample and the accuracy of the analytical tests.

6.1.2 Additional considerations in the selection of sample containers are the type of mixing required before transferring from the primary container, and the analysis to be performed. To facilitate the discussion on proper handling and mixing of samples, sample containers are referred to as either primary or intermediate containers. Regardless of the type of sample container used, the sample container should be large enough to contain the required sample volume and sufficient ullage space for thermal expansion and mixing of the sample.

6.1.3 While this practice is meant to provide some guidance related to particular products and tests, it remains the responsibility of the subcommittee for the relevant test method to provide specific guidance regarding sample container selection, preparation, cleanliness, and sample size requirements for testing and retention. Also refer to Practice D5854 (API MPMS Chapter 8.3), Practice D5842 (API MPMS Chapter 8.4), and Practice D4306.

6.2 Glass Bottles - See Fig. 7. Glass containers are suitable for many sample test and storage requirements. Clear glass bottles can be easily examined visually for cleanliness, and allow for visual inspection of the sample for haze (cloudiness), discoloration, free water, and solid impurities. The brown glass bottle affords some protection to the samples when light may affect the test results. Refer to Practice D5854 (API MPMS Chapter 8.3).

6.3 Cans - When using cans, any seams shall have been soldered on the exterior surfaces with a flux of rosin in a suitable solvent. Such a flux is easily removed with gasoline, whereas many others are very difficult to remove. Cans made of stainless steel with welded seams, and aluminum bottles, are suitable for many sampling operations, but cleanliness is still required. Minute traces of flux may contaminate the sample so that results obtained on tests such as dielectric strength, oxidation resistance, and sludge formation may be erroneous. For aviation fuel sampling, refer to Practice D4306.

6.4 Plastic Bottles - In general, plastic bottles made of suitable material may be used for the handling and storage of diesel oil, fuel oil, and lubricating oil. Bottles of this type should not be used for gasoline, aviation jet fuel, kerosene, crude oil, white spirit, medicinal white oil, or other petroleum products unless testing indicates there is no problem with solubility, contamination, or loss of light components. In no circumstances shall nonlinear (conventional) polyethylene containers be used to store samples of liquid hydrocarbons. This is to avoid sample contamination or sample bottle failure. Used engine oil samples that may have been subjected to fuel dilution should not be stored in plastic containers. Plastic bottles do have an advantage in that they will not shatter like glass or corrode like metal containers.

6.5 Container Closures:
6.5.1 Screw caps made of a material that will not deteriorate or contaminate the sample are to be used for glass bottles. Screw caps should provide a vapor-tight seal. Use care when using cork stoppers. Situations in which corks should not be used include: liquids in which loss of light ends may affect any test results; and liquids that are hygroscopic or have a low-water content specification. Rubber stoppers are not to be used.

6.5.2 Cans and plastic bottles should be closed with screw caps made of the same material as the container. Protect can screw caps with a disk faced with a material that will not deteriorate or contaminate the sample when used to store or transport samples. Consideration of closure type is important for samples in which vapor loss will affect the test results. Screw caps of a quality that provide a vapor-tight closure should be used for plastic bottles and cans. Use screw caps for containers used to take samples that will be tested for density or API gravity.

6.6 Container Cleanliness - Sample containers shall be clean and free from all substances that might contaminate the product being sampled (such as water, dirt, lint, washing compounds, naphtha and other solvents, soldering fluxes, acids, rust, and oil). Reusable containers shall be cleaned by a method that has been determined as acceptable for the intended use, for example by rinsing with a suitable solvent. Dry the container, for example either by passing a current of clean warm air through the container or placing it in a hot, dust-free cabinet at 40°C (104°F) or higher. When dry, stopper or cap the container. Normally, it is not necessary to wash new containers.

6.7 Container Compatibility for Sample Mixing - The sample container should be compatible with the mixing system for remixing samples to ensure that a homogenous sample is transferred to an intermediate container or the analytical apparatus. This is particularly critical with crude oil, some black products, and condensates for sediment and water (S & W) analysis. Cylindrical containers are generally better suited for samples that are to be tested for S & W. Refer to Practice D5854 (API MPMS Chapter 8.3) for sample mixing and handling requirements.

6.8 Low Pressure Variable Volume Containers - Low pressure variable volume sample container designs include collapsible plastics containers, bladders, and vessels fitted with a flexible internal diaphragm. Before use, variable volume sample containers are normally collapsed, evacuated or reduced to the nominal zero volume. The sample container size is dependent on the quantity required for analysis (and/or retention). Prior to use, it may be appropriate to rinse the sample containers with the product being sampled, in order to avoid contamination from previous sample residue and/or solvents used to clean the low pressure variable volume containers. The sample should be transported to the laboratory in the container in which it was originally obtained (the primary sample container). Plastics containers are not recommended for long-term sample storage, unless it has been demonstrated that the plastic is suitable (that is, compatible with the sample) so that the integrity of the sample is not compromised. (Warning - The use of containers made of non-linear polyethylene may lead to sample contamination and/or sample container failure.)

6.9 High Pressure Spot Sampling Systems and Cylinders:
6.9.1 Sample System Components - All equipment, such as transfer lines, valves and pressure gages, associated with sampling shall be corrosion resistant and designed consistent with the maximum anticipated pressure. Experience has shown that the transfer lines should have a minimum internal diameter of 3 mm (1/8 in.) nominal and be as short as practical to minimize line blockage or sample vaporization, or both. The use of filters, dryers, needle valves and related equipment are not recommended, unless provisions are made to prevent excessive flow restriction and pressure drop. It is recommended to use a "T" junction with a purge valve at the sample connection point to allow purging of the dead volume at the sampler connection. Flexible hose or tubing with adequate pressure rating may be used.

6.9.2 Cylinders - High pressure cylinders are used for the collection of light liquid hydrocarbons and gas samples and subsequent transportation and storage. Typical light liquid hydrocarbon sample containers are fixed volume cylinders or floating-piston cylinders (FPCs). Refer to Practices D1265, D3700, and D6849.

Fixed Volume Cylinder
6.9.2.1 Fixed volume sample cylinders are also known as single cavity sample cylinders or spun cylinders. Refer to Fig. 1 and Fig. 2.

6.9.2.2 Valves - Fixed volume sample cylinders are typically available with either one or two valves serving as cylinder inlet and outlet valves. Recommend using two-valve fixed volume sample cylinders due to their ease of cleaning and purging prior to sampling. For repeated use, it is recommended that one-valve fixed volume sample cylinders be used for only one product, due to difficulty in cleaning.

6.9.2.3 Internal Outage (Ullage) Tubes - It is recommend that fixed volume cylinders be equipped with an internal outage (ullage) tube, designed to provide a vapor space of typically 20 % of the cylinder capacity, allowing for liquid thermal expansion. The end of the cylinder fitted with the outage (ullage) tube shall be clearly marked. If the cylinder does not have an internal outage (ullage) tube, use alternative purging and venting procedures to obtain a minimum 20 % ullage in the cylinder. An internal outage tube within a fixed volume sample cylinder may also be known as an ullage tube or dip tube.

Sample Cylinder Usage Considerations
6.9.2.4 The type of sample cylinder used and its materials of construction as well as hoses and fittings can affect the validity of the sample, as well as the accuracy of the analysis.

6.9.2.5 When the observed vapor pressure of the liquid being sampled is close to the line pressure, the reduction in sample pressure associated with the creation of the ullage space may result in phase separation that can make subsequent representative sub-sampling difficult. In these circumstances, an FPC should be used to ensure that the sample is maintained at sufficient pressure to prevent phase separation.

6.9.2.6 Where small concentrations of contaminants need to be quantified or where concentrations of volatile compounds other than the predominant component need to be quantified, an FPC is recommended.

NOTE 2 - Practice D3700 describes a recommended practice for obtaining a representative sample of a light hydrocarbon fluid and the subsequent preparation of that sample for laboratory analysis when dissolved gases are present. Use of Practice D1265 using a fixed volume cylinder, will result in a small but predictable low bias for dissolved gases due to the liquid venting procedure to establish the 20 % minimum ullage.

6.9.2.7 Cylinder Construction - Cylinder construction is primarily dependent on the pressure and temperature of the product to be sampled, and the pressure vessel approval and certification requirements in the jurisdictions in which it is to be used and transported. All sample cylinder material, and equipment used for obtaining the sample, shall meet appropriate standards for construction, cleanliness and suitability for use, including product compatibility. Use corrosion resistant metal sample cylinders certified by the authority having jurisdiction for pressure vessels with adequate pressure rating for the product being sampled. Common materials used are non-magnetic 300-series stainless steel, Monel (trademarked), Viton elastomeric components, and possibly other materials. The size of the cylinder depends upon the amount of sample required to perform the anticipated laboratory tests, and to be retained. Blanking cover caps may be provided to seal the valve connection points of high pressure sample cylinders prior to their transportation between the sampling location and the laboratory.

Floating Piston Cylinders (FPC)
6.9.2.8 FPC, also known as a variable-volume cylinder or pressure-balanced piston cylinder, can be used to sample pure and multi-component liquids and when properly operated, maintains the sample as a single-phase liquid. This device uses one, or two pistons, inside of the sample cylinder to maintain separation between the liquid sampled and the backpressure inert gas. The two-piston cylinder is known as the double-piston cylinder (DPC). The inert gas is vented slowly to allow the sample to enter the cylinder while maintaining a constant pressure on the sample. FPCs are typically constructed from a honed metal tube equipped with end caps, valves, piston, a relief device to protect against over-pressure, and a method of displaying the piston position. See Fig. 8, Fig. 9, and Fig. 10.

6.9.2.9 Refrigerated Products - The FPC shall be safely cooled to the temperature of the product being sampled when sampling refrigerated liquids that are near or below atmospheric pressure. Low cargo temperature (more than approximately 15°C below ambient) and low cargo pressure (near atmospheric pressure) may affect the ability of the user to successfully capture a representative liquid sample using an FPC if additional care is not taken; and the use of a vacuum pump may be required. Refer to Practice D3700 and GPA S 2174.

6.9.2.10 Piston Position Indicator - The FPC shall be equipped with a piston position indicator such as a magnetic follower, piston rod, or equivalent that is used to indicate the sample volume to comply with the maximum percent fill (maximum fill density) allowed for storage and transportation. Do not use FPCs that are not equipped with a piston position indicator without a procedure to allow the operator to verify fill density immediately after sampling prior to transport. Consult the authority having jurisdiction for acceptable procedures. See Fig. 8 and Fig. 9.

6.9.2.11 Lubricants - Lubricants used to lubricate or seal the floating piston, O ring seals, and other components shall be inert to the product being sampled.

6.9.2.12 Cylinder Coatings - Some cylinders may be internally coated or lined to reduce the chances of bare metal surfaces reacting with trace reactive components, potentially altering the quality and integrity of the sample. For example, be absorbed into the structure of 316 stainless steel, so that testing for H2S may require the cylinder to be coated. Protective internal coatings or surface treatments are acceptable for FPCs provided that they do not adversely affect the free movement of the piston, or effectiveness of the seals.

Cylinder Pressure Relief
6.9.2.13 Fit a ruptured disk or a self-resetting pressure relief valve to the cylinder to prevent overpressure as the result of liquid thermal expansion. It is recommended to use a spring relief valves if self-resetting is required. Typically, the maximum operating system pressure should be limited to 80 % of the nominal rating of the rupture disk for static operating pressure and ambient temperature. The relief maximum burst pressure shall not exceed the cylinder test pressure. Refer to applicable regulatory requirements for safe filling limits.

6.9.2.14 Cylinder Pressure Relief Inspection - The strength of rupture disks can deteriorate with time due to temperature, corrosion, and fatigue. In addition, pulsating pressure, vacuum/pressure cycling, heat, and corrosive fluids and atmospheres can reduce the disk's burst pressure. Relief valves and rupture disks should be inspected regularly. Do not alter valves or safety relief devices that are part of a cylinder permit or exemption.

NOTE 3 - The USA has an exemption system, and Canada has a permitting procedure for non-American Society of Mechanical Engineers (ASME) or Department of Transportation (DOT) cylinders.

6.9.2.15 Cylinder Pressure Relief Release - The sudden release, typically accompanied by a loud noise and product released at high velocity, might create a hazard. If the sample cylinder pressure exceeds the relief device setting and part of the sample cylinder contents are vented, the composition of the remaining sample is likely different from the original contents. Another sample should be drawn and procedures revised to avoid the circumstances that led to the overpressure condition.

6.9.3 Cylinder Approval and Rating - If the cylinder is to be transported, it shall also conform to specifications published in transportation legislation such as U.S. CFR 49 or Canadian Transportation of Dangerous Goods Regulations, and their supplements, reissues, or similar regulations in other jurisdictions.

6.9.4 Cylinder Extreme Temperature Considerations - For safe handling of cylinders under extremes of product or ambient temperatures, or both, the user shall consider the effects of thermal expansion on the volume of product in the cylinder. For example, if a very cold (e.g. -40°C (-40°F)) product is sampled, the cylinder should be expected to warm considerably before analysis is performed during transport and in the laboratory. During summer months, the temperature of the cylinder and product could reasonably be expected to rise to as high as 46°C (115°F) in hot environments. A cylinder initially filled to 80 % of its capacity will be over pressured and the relief device(s) will activate under these conditions. In such an extreme but not uncommon case the cylinder should not be filled more than approximately 60 % during the initial fill. The appropriate industry volume correction factor data and calculations should be consulted to determine the maximum fill for the product being sampled. It is recommended that users work with the manufacturer of these sample cylinders and sample collection systems any time ambient or product temperatures, or both, exceed the range of -29°C (-20°F) to 60°C (140°F). Consider the effects of extreme temperature on metal, O-rings, valve seats, seals, gauges, relief devices, sample pump components and other devices and components in the system.

6.9.5 Mixing Capability - The cylinder may include a mechanism to mix the sample in the sample chamber in case of stratified mixtures or water haze that may settle after sampling. This mechanism may be a mechanical mixer/vortex plate on a movable rod, a freely moving rolling ball or slider, magnetically coupled stirrer, or similar device. Some designs of FPCs have two pistons, which enable the sample to be mixed within the cylinder (prior to sub-sampling) by repeatedly forcing it through a central mixing device. See Fig. 9 and Fig. 11.

6.9.6 Sample Cylinder Cleanliness - To ensure the sample cylinder and its components do not affect the integrity and quality of the sample obtained, the user shall establish an acceptable cylinder cleaning and preparation process based on experience, and considering the following factors:
(1) Type of cylinder and design,
(2) Cylinder material and lining,
(3) Cylinder components (valves, seals, etc.) and attached tubing/lines,
(4) Recent history of the cylinder, including repair or last product,
(5) Product being sampled,
(6) Product test methods,
(7) Purity of product being sampled, and concern with trace contaminants, and
(8) Use of cleaning agents.

6.9.6.1 Sample Cylinder Cleaning and Purging Methods - Based on the above factors any one, or combination, of the following may be deemed as satisfactory cylinder cleaning methods:
(1) Purging and flushing of the cylinder using a cleaning agent or solvent, for example acetone or methanol. It is recommended to purge and flush the sample cylinder at least three times.
(2) Purging and flushing of the cylinder using an inert gas, such as helium and nitrogen. Testing of the inert gas present in the cylinder is recommended to confirm no trace of hydrocarbon gas or impurities. It is recommended to purge and flush the sample cylinder at least three times.
(3) Purging and flushing of the cylinder using the product being sampled. It is recommended to purge and flush the sample cylinder at least three times.
(4) Steam (not recommended for floating piston cylinders).
(5) Warming and drying of cylinders.
(6) Manufacturer's recommendations.

6.9.6.2 Cylinders used in continuous service, for example with specification LPG products or stabilized crude, may not require disassembly or cleaning before each use. For example, it may be acceptable to vent the previous product as a liquid, and remove remaining sample from dead volume by solvent rinsing, evacuation, gas purge, or equivalent procedure. (Warning - Disassembly of the piston cylinder for maintenance requires special precautions. If either end cap is removed while pressure is on the cylinder, the end caps and the piston can be ejected with such a force as to cause serious injury to personnel and damage to equipment. Consult the manufacturer's instructions, and regulatory guidelines, for the maintenance and safe disassembly instructions for all cylinders.) Refer to Practice D6849.

6.10 Special Sample Cylinders - Specially designed single purpose sample cylinders are often used for non-compositional tests, the testing of trace constituents using specific instruments, and physical property testing devices. Refer to Test Method D1838, Test Method D1267, API MPMS 14.6, and Test Method D1657 (API MPMS Chapter 9.2) for details. In addition, spot samples may be tested for some components, including trace analysis using length-of-stain tubes, gas content using lower explosive limit or gas detectors, oxygen content using oxygen detectors and trace oxygen analyzers, and moisture content using dew point instruments. Refer to manufacturer's instructions and appropriate industry standards for use and applicability.