GB/T 4756-2015 Manual sampling of petroleum liquids

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Card type: Test method

1. Method number / full title / English title / replacement relationship

• Standard number: GB/T 4756—2015
• Chinese title: Manual sampling of petroleum liquids
• English title: Method for manual sampling of petroleum liquids
• Adoption relationship: Modified adoption using the redrafting method of ISO 3170:2004 "Petroleum liquids — Manual sampling" (MOD)
• Replacement relationship: Replaces GB/T 4756—1998 "Manual sampling of petroleum liquids"
• Publication/implementation: Published on 2015-12-31, implemented on 2016-06-01
• Custodianship: Subcommittee on Static Petroleum and Light Hydrocarbon Measurement of the National Technical Committee for Standardization of Petroleum Products and Lubricants (SAC/TC 280/SC 2)
• Drafting organizations: Responsible for drafting by the Research Institute of Petroleum Processing, China Petroleum & Chemical Corporation; participated in drafting by Luoyang Petrochemical Engineering Company, China Petroleum & Chemical Corporation
• Main drafters: Wei Jinxiang, Liu Fengyang
• Version history: First published in 1984 year 11 month, first revision in 1998 year 6 month, this is the second revision

2. Scope of application and non-applicability

• Scope of application (Chapter 1): Specifies manual sampling methods for collecting liquid or semi-liquid hydrocarbon, tank residue and sediment samples from fixed tanks, railway tank cars, road tank cars, ships, drums, cans, pumped liquid pipelines or fuel dispenser nozzles.
• Applicable conditions: Applicable to sampling of petroleum products, crude oil and intermediate products stored in tanks at atmospheric pressure or near atmospheric pressure or transported by pipeline, and stored and transported in liquid form within the range from normal temperature to 200 ℃.
• Not applicable: Not applicable to sampling of special petroleum products that are the subject of other standards, such as electrical insulating oils (IEC 60475), liquefied petroleum gas (SH/T 0233), liquefied natural gas (GB/T 20603) and gaseous natural gas (GB/T 13609).
• Note (Chapter 1): This standard may also be applicable to sampling of most non-corrosive liquid chemical products, but the safety measures corresponding to these liquid chemical products should be strictly observed.
• Differences from 1998 version (Foreword): The scope adds content on manual sampling from fuel dispenser nozzles; the upper temperature limit for storing and transporting sampled products in liquid form is changed from 100 ℃ to 200 ℃, and the provision on Reid vapor pressure of products is deleted.

3. Method principle

• Principle (4.1): To ensure that the sample submitted for inspection represents the sampled liquid as much as possible, this standard specifies necessary precautions; these precautions depend on the properties of the liquid, the tank, container or pipeline being sampled, and the test items of the sample.
• Manual sampling methods are mainly divided into two types: tank sampling (static sampling) and pipeline sampling (dynamic sampling). When receiving or issuing a batch of oil, tank sampling or pipeline sampling may be selected, or both may be used; when both methods are used, the two sets of samples should not be mixed.
• Tank sampling (4.2): Tank sampling may be carried out only when the liquid in the tank is static. Usually one of the following samples is collected: a) upper sample, middle sample and lower sample; b) upper sample, middle sample and suction level sample (outlet liquid level sample). If inspection shows that the tank liquid is uniform, the samples may be mixed in proportion to the volume represented by each sample; if inspection shows that it is not uniform, spot samples should be collected at more than three liquid level sampling points to prepare a composite sample; when sample compositing would impair sample integrity, each sample should be analyzed separately and the result equivalent to the composite sample should be calculated. Other methods are routine sample or all-level sample, which only obtain a single sample and cannot be used to evaluate the uniformity of the liquid in the tank; they are usually used to determine the average quality of the liquid in the tank.
• Pipeline sampling (4.3): To obtain a representative sample of a batch of transferred liquid from a transportation pipeline, an automatic sampling device should be used for sampling in accordance with GB/T 27867; in some cases, only a limited number of spot samples in a dynamic pipeline can be collected manually, and the samples obtained may not represent the bulk liquid being transferred.
• Introduction: This standard aims to standardize manual sampling of liquid/semi-liquid hydrocarbons in oil storage containers or transportation pipelines; the specified methods can reduce and eliminate loss of light components in samples; it is intended to provide samples for three purposes: determining liquid/hydrocarbon characteristic parameters, determining water content, and determining other impurities not belonging to the transferred liquid; if the sampling methods for the three purposes conflict with each other, samples suitable for each should be collected separately.

4. Reagents and materials (purity / preparation)

• No clauses on chemical reagent purity/preparation are provided in the available source.
• Related material requirements (5.5, 5.6): Fixed-volume sample containers may be glass bottles, suitable plastic bottles, metal-sheathed bottles or cans; depending on the purpose of use, metal containers may need to be lined with a suitable coating; internally painted cans or drums may also be suitable. Container closures may use cork stoppers, plastic or metal screw caps; natural rubber stoppers should not be used; cork stoppers should be of good quality, free from loose fragments or dust, and softened by rolling or pressing; when collecting volatile samples, it is recommended to preferentially use screw caps with compressible sealing gaskets instead of cork stoppers; cork stoppers should not be reused (allowed only when used for one product); screw caps of cans or bottles should be equipped with cork discs or compressible plastic sealing rings made of oil-resistant material, and cork discs should be used only once.
• Plastic containers (5.5): Should not be used for long-term sample preservation unless it has been demonstrated that the plastic is suitable for the sample being stored; containers made of non-linear polyethylene may cause sample contamination and/or damage to the sample container.
• Inert gas (7.4.3): Used for pre-pressurization of variable-volume/fixed-volume receivers, filling control and leak testing (for specific pressure requirements see Section 8).

5. Apparatus and equipment

• 5.1 General: Sampling devices should be designed with leak-proof characteristics, and manufacturing should ensure that design requirements are met; they should have sufficient strength and external protection to withstand possible normal internal pressure and possible external forces; before use, it should be confirmed that cleanliness requirements are met. Note: In some cases, it is advisable to rinse the sample receiver/equipment with the liquid being sampled (only suitable for liquid hydrocarbons); 5.2 to 5.7 describe various sampling devices and necessary appearance requirements, but detailed specification requirements are not listed.
• 5.2 Tank samplers
  • 5.2.1 General: Classification is based on the type of sample extracted (spot sample, interval sample, routine sample, all-level sample) and tank operation and sampling entry mode (open sampling, restricted sampling, closed sampling). Because electrostatic sparks may be generated, ropes made of synthetic fiber should not be used to lower and raise samplers in tank liquids. Note: To ensure continuous grounding of the sampler, it is not advisable to use metal chains to suspend the sampler.
  • 5.2.2 Spot samplers and interval samplers: Should have a suitable structure and be capable of collecting samples at any specified position in the tank.
    • 5.2.2.2 Sampling cage: A fixed frame made of metal or plastic material that can hold a suitable container such as a bottle or can; weighted to make it easier to sink into the sampled product; means should be provided to fill the container with sample at a specified liquid level (see Figure 2). Some bottle cages can accept sampling bottles with different neck sizes (or volumes) and are equipped with a float system so that once the bottle is full, the float immediately seals the bottle mouth. Note: For volatile products, sampling bottle cages should be preferentially used instead of other single-point sampling methods; when a weighted rope can be securely tied to the sample bottle, the sampling cage may not be used, and the bottle stopper should also be tied to a cord about 150 mm from the neck of the sampling bottle.
    • 5.2.2.3 Weighted sampling bucket: Adds extra weight to the sampling bucket (see Figure 3) to make it easier to sink into the sampled liquid; connect the suspension device to the bucket as shown in Figure 3, and open the stopper of the sampling bucket by jerking; to avoid problems during bucket cleaning and/or possible contamination of sensitive samples, the weight should be fixed to the bucket in a manner that does not contact the sample.
    • 5.2.2.4 Interval/liquid core sampler: Consists of a tube made of glass, metal or plastic material, open at both ends, through which liquid can flow freely while being lowered into the liquid; at the required liquid level, the lower port of the sampler can be closed by various devices: a) a closing mechanism activated by upward movement of the sampler; b) a closing mechanism activated by a weight dropped along the suspension cable; c) a trigger-type closing mechanism controlled by a float; d) a closing mechanism activated by an extension rod or jerk line. The design and manufacture should enable it, when lowered slowly, to collect a vertical liquid column at any selected liquid level (including the tank bottom) (see Figure 4 and Figure 5). Note: An interface sampler is a special type of interval sampler used to collect a vertical liquid column at the oil/water interface position at the tank bottom or any other selected liquid level, such as the oil slick interface on ballast water in oil tankers, but it can also be used to collect interval samples from any selected liquid level in the tank (see Figure 6).
  • 5.2.3 Bottom sampler: A container placed at the bottom of the tank, which opens the valve by contacting the tank bottom plate and closes the valve automatically when lifted (see Figure 7); some samplers have extendable "feet" that allow sampling just above a layer of sediment. Note: Some interval/liquid core samplers or interface samplers can also be used as bottom samplers.
  • 5.2.4 Residue/sediment samplers
    • 5.2.4.1 Sediment sampler: Two types are commonly used, both the grabbing device and the suction device are spring-driven; a typical example is shown in Figure 8.
    • 5.2.4.2 Heavy hammer sampler: A tubular device of uniform diameter that drills the sampled sediment by gravity or mechanical power.
  • 5.2.5 Routine sampler: A container equipped with a restricted filling device that obtains a sample while being lowered and raised in the liquid. Note 1: The reason why constant-rate filling of routine samplers cannot yet be established is: a) tank volume may not be proportional to depth; b) the operator cannot raise (or lower) the sampler at the variable rate required for uniform filling, which rate should be approximately proportional to the square root of the immersion depth. Note 2: A fixed-volume routine sampler may be based on a sampling bottle cage or weighted sampling bucket, and some products provide a series of selectable small holes to adapt to different oil depths and viscosities. Note 3: For a variable-volume routine sampler, the capacity of the initial sample receiver increases with the distance traveled in the tank liquid; as long as it is demonstrated that the sampler can fill at a constant rate while moving in the liquid, this device is acceptable.
  • 5.2.6 All-level sampler: A container equipped with a restricted filling device that obtains a sample while moving in only one direction in the liquid. Note 1: The reason why constant-rate filling of all-level samplers cannot yet be established is the same as Note 1 to 5.2.5. Note 2: These devices may be similar to those used to collect routine samples, or may be specially designed products for obtaining such samples. Note 3: A "bottom-up" fixed-volume all-level sampler is based on a sampling bottle/cage (or weighted sampling bucket); the sampler opens when placed near the bottom of the tank, and the sample is collected into the sampler when lifted. Note 4: Some dedicated "top-down" and "bottom-up" fixed-volume all-level samplers are equipped with different opening/closing switches; to adapt to different oil depths and viscosities, the inward flow rate may also be restricted in other ways; a typical example of a "top-down" fixed-volume all-level sampler is shown in Figure 9. Note 5: Variable-volume all-level samplers may also be used effectively; as long as it is demonstrated that the sampler can fill at a constant rate while moving in the liquid, this device is acceptable.
  • 5.2.7 Restricted and closed system samplers: When safety and/or environmental constraints limit the use of tank opening sampling equipment and methods, samples may be collected using restricted or closed system samplers installed on vapor lock valves; particularly suitable for pressure tanks, tanks with inert gas blanketing above the liquid surface, and/or tanks with vapor balance/recovery systems. Some samplers are designed to collect spot samples, interval samples, interface samples, bottom samples, routine samples, and all-level samples under restricted and/or closed conditions; connect the sampler to a graduated steel tape or cable, then insert it into a portable sampling device equipped with a winding mechanism (PSD), and then connect the entire apparatus to the vapor lock valve (typical example shown in Figure 10). Restricted equipment is designed to substantially reduce vapor emissions when the vapor lock valve is opened, but does not provide dedicated attachments for sample conditioning or transfer operations after the vapor lock valve is closed, so a small amount of vapor may be emitted to the atmosphere. Closed equipment should be designed to be completely vapor-tight at all times, and typically provides dedicated configurations for portable closed sampling devices: ensuring vapor-tight connections; enabling sample transfer to other receivers without vapor loss. Other configurations may also be provided: returning vapor retained in the sleeve to the tank or absorption tank; or purging the system with inert gas. Note: Whether a fixed-volume sample receiver obtains a representative routine sample or all-level sample (i.e., not completely filled), closed systems generally do not have the conditions for visual inspection.
• 5.3 Drum and can samplers: Tubular samplers are commonly used for sampling from drums and cans (see Figure 11), made of glass, metal, or plastic tubes; installing suitable fittings on them makes handling more convenient. Before inserting the tubular sampler into the drum or can to the specified liquid level, temporarily close the upper opening with the thumb to obtain a spot sample or bottom sample; when the tube reaches the required liquid level, remove the thumb from the upper opening to allow the sample to fill the tube; when filling is complete, close the upper opening again with the thumb, remove the sample and transfer it to another sample receiver. If the tube has a uniform cross-sectional area along its entire length, it can also be used to obtain interval samples or core samples from the entire liquid height in a drum or can; slowly lower the tubular sampler from the opening position so that the inflow rate of the sample equals the descent rate of the sampler to collect these samples; when filling is complete, close the upper port, remove the tubular sampler, and transfer the sample to another sample receiver. A more advanced tubular sampler has a lower port closing mechanism and can be used in a similar manner to collect representative interval samples or core samples. Due to the risk of light component loss, it is recommended not to use a pump or siphon device to extract volatile oils, and do not siphon oil with the mouth.
• 5.4 Pipeline samplers
  • 5.4.1 When using automatic pipeline samplers, the provisions of GB/T 27867 shall be complied with.
  • 5.4.2 Manual samplers include a suitable sampling tube with an isolation valve; the sampling tube should extend into the transfer pipe, and the distance from the sampling point to the pipe wall shall not be less than one quarter of the inner diameter; the inlet of the sampling tube should face the flow direction of the liquid being sampled in the pipeline (see Figure 12). If the sample is injected into a fixed-volume sample container (e.g., a bottle), the outlet valve of the sampling tube should be fitted with a discharge tube of sufficient length to reach the bottom of the sample container for submerged filling. If the sample is injected into a variable-volume sample receiver (e.g., a floating piston cylinder), the outlet valve of the sampling tube should be fitted with a drain tube and connecting line to allow safe flushing of the sampling tube and connecting line and to accumulate the sample in the sample receiver. In Figure 12: sampling tube with closed end, opening facing upstream, tube diameter 6.4 mm–50 mm; tube with diameter 6.4 mm–50 mm; 45° bevel angle.
• 5.5 Sample receivers and sample containers: Fixed-volume sample containers depend on the product being sampled and may be glass bottles, suitable plastic bottles, metal-sheathed bottles or cans; depending on the intended use, metal containers may need to be lined with a suitable coating; internally painted cans or drums may also be suitable as sample containers. Variable-volume sample receivers can be designed as low-pressure or high-pressure types; low-pressure types include compressible plastic containers, bladders, and containers with elastic internal diaphragms; high-pressure variable-volume sample receivers are pressure vessels with an internal piston, which moves against a gas buffer as the sample accumulates on the other side of the piston, a typical example (floating piston cylinder) is shown in Figure 13. Note: Some types of high-pressure variable-volume sample receivers have two pistons, and before extracting a subsample, the sample can be mixed within the receiver by repeatedly pushing the sample through a central mixing device (Figure 14). Before use, variable-volume sample receivers are typically compressed, evacuated, or reduced to nominal zero volume (by injecting inert gas on the opposite side of the diaphragm or piston); the sample is accumulated by compressing the inert gas or carefully reducing the inert gas pressure, and the sample volume increases accordingly. The volume of the sample receiver/container depends on the amount of sample required for the test analysis (and/or the retained sample). Before each use, it is advisable to rinse the sample receiver and sample container with the liquid being sampled to avoid contamination of the current sample by residues from previous samples and/or solvents used to clean the container. The sample should preferably be transported to the laboratory in the original container in which it was obtained, and methods that do not require transferring the sample to another container should be preferred.
• 5.6 Container closures: see Section 4.
• 5.7 Sample coolers: The cooling coil is made of seamless copper tubing or other suitable metal tubing of suitable inner diameter, and should be installed in an open portable container; during use, the cooling coil must be immersed in water or an ice-water mixture in the container; in addition, the cooling coil may also be installed in a closed container with circulating coolant. The inlet of the tube should be connected to the sampling valve via a flange or other suitable connection, and the outlet should be open. Before collecting samples that require cooling, the sample cooler should be effectively flushed. Note that the sample cooler should be used correctly (see 7.2.3.2).

6. Recommended operating conditions

• Temperature range (Chapter 1): Applicable to petroleum products, crude oil, and intermediate products stored and transported as liquids in the range from normal temperature to 200 ℃.
• Tank sampling conditions (4.2): Tank sampling may only be carried out when the liquid in the tank is at rest.
• Cooling of volatile products (7.2.3.2): Depending on the liquid properties, liquid temperature, ambient temperature, and sampling purpose, some or all of the following precautions should be taken: a) pass the sample through a sample cooler at the sampling point; b) before sampling, cool the sample container to a suitable temperature; c) keep the sample container cool until it is closed; d) keep the sample container cool until transported to the laboratory. If necessary, the sample container may be immersed in an ice-cold medium (e.g., crushed ice) for cooling, but attention should be paid to whether sample cooling causes partial separation of wax and/or other heavy components. Sample cooling may cause wax or heavy components to deposit on the walls of the sample container, and subsequent subsamples may no longer represent the entire original sample. Crude oil samples should not be cooled below a temperature value of 3 ℃ above its wax precipitation temperature. For example, when the wax precipitation temperature is above ambient temperature, the sample should be warmed before sample division.
• Additional precautions for tank-side and pipeline sampling (7.2.4): a) Before taking tank-side or pipeline samples, thoroughly flush the sampling line (with at least one line volume of liquid) to ensure removal of all previously existing substances in the line; b) When filling a fixed-volume sampling container, the outlet of the sample line should extend to the bottom of the sample container during sampling; when filling a variable-volume sample receiver, facilitate flushing of all sample lines upstream of the receiver inlet valve; c) If the product being sampled is volatile, cool the sample container to a suitable temperature, and when necessary and appropriate (see 7.2.3.2), use a sample cooler (see 5.7); d) If the crude oil being sampled has a high pour point, it may be necessary to insulate the sample line or provide a means to heat the sampling line to prevent the oil from solidifying.
• Number and interval of manual fixed-point pipeline sampling (7.4.2): When sampling by quantity of oil transferred, when the quantity does not exceed 1000 m³, take 1 samples each at the beginning and end of transfer; when the quantity exceeds 1000 m³, take 1 samples at the beginning of transfer, and thereafter take 1 samples every 1000 m³. When sampling by transfer time, when the transfer is less than 1 h, take 1 samples each at the beginning and end of transfer; when the transfer is from 1 h~2 h, take 1 samples each at the beginning, middle, and end of transfer; when the transfer time exceeds 2 h, take 1 samples at the beginning of transfer, and thereafter take 1 samples every 1 h. Note: The beginning of transfer means the oil in the tank flows past the sampling port 10 min, and the end of transfer means 10 min before stopping transfer.
• Pressure control for fixed-point sampling of high vapor pressure liquids (7.4.3): Single-piston receivers are pre-pressurized to at least 100 kPa above pipeline pressure; during filling, the pressure difference between the sample side of the piston and the inert gas buffer side should not exceed 100 kPa; after filling, the inert gas pressure is increased to at least 100 kPa above pipeline pressure. Dual-piston receivers are pre-pressurized to at least 500 kPa above pipeline pressure; during filling, the pressure difference between the pipeline and the operating inert gas buffer should not exceed 100 kPa; after filling, the inert gas pressure is increased to at least 100 kPa above pipeline pressure. Fixed-volume receivers are leak-tested by pressurizing to at least 100 kPa above the expected pipeline pressure; after sampling, a gas space of 20% should be provided in the receiver immediately.
• Dispenser (nozzle) sampling (7.5): Fit the nozzle with an extension tube so that the fuel reaches the bottom of the sample container directly without splashing; where the nozzle is equipped with a vapor recovery system, a gasket is needed to press down the nozzle sleeve; slowly inject the sample through the nozzle extension tube into the sample container until the container is filled to about 85% of its volume; remove the nozzle and its extension tube, and immediately close or cap the sample container; when sampling for vapor pressure analysis, the sample container should be pre-cooled before filling.

7. Sampling and sample preparation

• Spot sampling positions (Figure 1): 1— top sample; 2— oil surface; 3— skim sample; 4— upper sample; 5— middle sample; 6— suction level sample or outlet level sample; 7— lower sample; 8— bottom sample; 9— drain pit sample.
• Minimum specified number of spot samples (Table 1): Liquid level (L)/m classification L≤3, 3<L≤4.5, L≥4.5; the number and positions of sampling points include upper, middle, and lower (in the table, “X” represents the sampling point, and the specific correspondence requires confirmation against the source standard (source-text extraction)).
• Location of term definitions (Chapter 3): The top sample is a spot sample obtained at a position 150 mm below the top liquid surface; the upper sample is a spot sample collected at one-sixth of the liquid depth below the top liquid surface; the middle sample is a spot sample collected at one-half of the liquid depth below the liquid surface; the lower sample is a spot sample collected at five-sixths of the liquid depth below the liquid surface; the bottom sample is a spot sample collected from the product at or near the bottom of a tank or container; the suction level sample/outlet level sample is a sample collected from the lowest level at which liquid hydrocarbon is pumped out of the tank; the skim sample/surface sample is a spot sample collected from the liquid surface; the interval sample is a sample collected by placing an interval sampler at a certain position in the tank, closing the sampler after the liquid has completely filled it, and at that time collecting the sample accumulated in the liquid column portion within the total height of the sampler.
• Fixed tank sampling (7.3.1.1): vertical cylindrical tank spot sample, composite sample, bottom sampling, interface sampling, valve (tank side) sampling, all-levels sample, running sample; horizontal tanks shall be sampled at the positions specified in Table 2; tanks of other geometric shapes shall be sampled according to 7.3.1.1.1, and the actual liquid level for collecting the sample shall be determined according to the volume distribution over the tank height; tanks equipped with vapor lock valves shall use PSD; pressure tanks with valve sampling points may use one of the pressure receiver sampling methods described in 7.4.3.
• Horizontal tank sampling (Table 2): the correspondence among liquid depth (percentage of diameter), sampling position (percentage of diameter above the tank bottom), and composite sample (proportions of each part); the table lists levels such as 100, 90, 80, 70, 60, 50, 40, 30, 20, 10 (the specific numerical correspondence requires confirmation against the source standard (source-text extraction)).
• Tanker compartment sampling (7.3.2): For a tanker composed of multiple compartments and carrying the same crude oil and liquid petroleum products, sampling should be carried out in every compartment as far as possible; when sampling in all compartments is not possible due to various constraints, after negotiation among the parties involved in the transfer, random sampling as described in 11.1.4 may also be carried out, but the first compartment shall be included.
• Railway tank cars (7.3.3): For a train of railway tank cars loaded with the same product, if the parties agree to accept sampling from a limited number of tank cars, sampling shall be carried out from the tank cars selected according to a sampling plan conforming to the general method described in 11.1.4, but the first car shall be included.
• Road tank cars (7.3.4): Sampling shall be carried out according to the corresponding method for horizontal tanks (see 7.3.1.2) or tanks of other geometric shapes (see 7.3.1.3); when a restricted or closed system sampling is required, the method described in 7.3.1.4 shall be used.
• Pipeline sampling (7.4): general principles, homogeneous liquids, spot sampling of high vapor pressure liquids (single-piston variable-volume sample receiver, dual-piston variable-volume sample receiver, fixed-volume sample receiver).
• Sampling of crude oil and other non-uniform petroleum liquids (Chapter 8): Tank sampling shall use one of the spot sample, running sample, or all-levels sample specified in 7.3; when the parties reach agreement, a composite sample of spot samples or interval samples may be prepared (see 7.3.1.2); pipeline sampling shall use the automatic pipeline sampling method specified in GB/T 27867; when manual sampling has to be used, corresponding consideration shall be given to the selection, installation, and operation of the sampling equipment (see 8.2.2.1).
• Sample conditioning (Chapter 9): general principles, sample homogenization, verification of stirring effect, sample transfer (the specific clause contents are not provided in the available source).
• Sampling of tank residues/deposits (Chapter 10): the specific clause contents are not provided in the available source.
• Package sampling (Chapter 11): statistical viewpoint of package sampling, package sampling methods (the specific clause contents are not provided in the available source).

8. Analytical procedure

• Fixed tank spot sample (7.3.1.1.1): Lower the sampler into the liquid until its opening reaches the required liquid depth, open the sampler in an appropriate manner, keep it at the required liquid depth position until it is full; withdraw the sampler, and before sealing the sample, pour out part of the liquid in the sampler to establish a gas space inside the sampler, or carefully transfer all of the sample to another sample container. Note: If part of the liquid in the sampler is poured back into the tank, adhering material on the gauge line may flow into the tank with the liquid, and its effect on subsequent sampling and safety should be considered; if necessary, it may be poured into another container. Under hotter climatic conditions or when there is a large difference between the temperature of the sampler and the temperature of the product being sampled, before opening the opening device of the sampler, the sampler should be slowly raised and lowered within a height range of about ±300 mm for 1 min~2 min to adjust it to the temperature of the liquid in the tank. When sampling at different liquid depths, sampling should be carried out in order from top to bottom to avoid disturbance of the liquid at lower depth positions. For an interval sampler, lower the sampler in a controlled manner until it is at the required liquid depth; once the descent stops, the valve closes immediately, and the sample should be withdrawn immediately; carefully transfer all of the sample to another sample receiver. When the design of the interval sampler cannot satisfy full cross-sectional flow of liquid through the sampler during descent, it is recommended to raise and lower the sampler two or three times at the sampling position before closing the valve, and the raising and lowering distance should be at least the height of the sampler. When collecting a top sample, carefully lower the open sampler/container until the opening of the sampler is just above the liquid surface, then let the sampler descend rapidly to a position 150 mm below the liquid surface; when the cessation of bubbles indicates that the sample is full, withdraw the sampler and proceed as for an ordinary spot sample.
• Composite sample (7.3.1.1.2): A composite sample may be prepared from subsamples of representative spot samples obtained within a single tank, or a composite sample may be prepared by combining subsamples representing each tank for a bulk oil product originating from them; the composite sample shall include all material collected in the initial sampling device that has not been split; in order to add the entire contents of the initial sampling device to the volume of the other subsamples in the transport container, the amount of sample collected by the initial sampling device should be selected; when the subsample amount of the composite sample is less than the total amount of one subsample, sample compositing should be performed only in a laboratory that can ensure sufficient mixing and measurement of the subsamples. To prepare various composite samples, transfer the subsamples representing each sample into the composite sample container, and then slowly mix them together; the subsamples should be volume-weighted according to the quantities they respectively represent. When the subsamples to be combined originate from tanks with non-uniform cross-sectional area (or from multiple tanks), the compositing operation requires careful calculation and measurement of the subsamples to maintain the representativeness of the sample; these operations should be carried out under controlled laboratory conditions. Note: Evaporation of light components and adherence of water/sediment to the initial sampler can affect the representativeness of the composite sample (see 7.2.3). Unless specifically required and agreed by the relevant parties, a composite sample for testing shall not be prepared; as an alternative to physical compositing, each spot sample may be tested separately, and the average of the test results calculated according to the quantity represented by each sample.
• Bottom sampling (7.3.1.1.3): Lower the bottom sampler until it rests vertically above the tank bottom, the valve then opens, and liquid flows into the sampler; after withdrawing the sampler, strictly check it for leakage; if leakage is found, discard this sample, clean the bottom sampler, and sample again; if necessary, the contents of the initial bottom sampler may be transferred to another sample container, but it should be ensured that all of the sample is thoroughly transferred, including water or solid matter that may adhere to the inner wall of the sampler.
• Interface sampling (7.3.1.1.4): Place the sampler with the valve open into the liquid so that the liquid flows through its interior; at the required depth, close the valve and withdraw the sampler from the liquid. If a transparent tube is used, the current interface can be observed through the wall of the sampling tube, and its corresponding position in the tank can be determined from the reading of the sampling tape connected to it; check whether the valve is completely closed, otherwise sampling should be repeated. Note: This sample may be retained for test analysis.
• Valve (tank side) sampling (7.3.1.1.5): This method is not the best method used in oil transfer and inventory management and should be used only when no other sampling method is available. The valve at the sampling point should have a minimum diameter of 12.5 mm and should be installed on the side of the tank at specified intervals, and its connecting pipe should extend into the tank at least 150 mm, except for floating roof tanks where a connecting pipe cannot be installed; the lower connecting pipe and the bottom of the suction pipe should be at the same height (see 7.2.4). Before sampling, flush the valve connecting pipe with the product being sampled, and then collect the sample into a container or receiver. Warning—When sampling under pressure, open the valve carefully; do not attempt to clear a blocked connecting pipe through an open valve by poking with a rod. If the tank is equipped with three connecting pipes and the liquid in the tank has not reached the upper or middle sample connecting pipe, samples shall be collected as follows: a) when the liquid level is between the middle and upper sample connecting pipes and closer to the upper connecting pipe, two-thirds of the sample should be taken from the middle connecting pipe and one-third from the lower connecting pipe; b) when the liquid level is between the middle and upper sample connecting pipes and closer to the middle connecting pipe, one-half of the sample should be taken from the middle connecting pipe and one-half from the lower connecting pipe; when the liquid level is below the middle sample connecting pipe, all of the sample should be taken from the lower connecting pipe.
• All-levels sample (7.3.1.1.6): All-levels samplers include two types: "top-to-bottom" or "bottom-to-top"; the sample receiver is filled with sample as it passes through the liquid in the tank in one direction, but the operating methods of the "top-to-bottom" and "bottom-to-top" samplers are different. To obtain a (bottom-to-top) all-levels sample by means of a bottle equipped with a weighted sampling cage (or a weighted sampling bucket): close the stopper of the bottle or bucket, lower it to the tank bottom (avoiding free water at the bottom); jerk the cord, open the stopper, and at a uniform rate without pausing, raise the sampler back to the liquid surface; when raising the sampler from the liquid, select its moving speed so that the bottle or bucket is filled to 80%, but not more than 90%; immediately close the stopper tightly, or carefully transfer all of the sample from the weighted sampling bucket to another carrier container (see 5.2.6). When withdrawing a fixed-volume all-levels sampler from the liquid, if it is less than 90% full, it may be assumed that oil flowed into the sampler from all depths during its passage through the liquid in the tank; when withdrawing the sampler from the liquid, if the sampler is filled above 90%, the sample may not be representative, and the sample taken should be discarded and sampling repeated with a faster lifting speed. Note 1: The use of a fixed-volume all-levels sampler is not the best sampling method in trade transfer and production inventory; such a device cannot be filled with sample at a uniform rate; in addition, it is difficult for the operator to lower or raise the sampler at the rate required for balanced filling, which rate is approximately proportional to the square root of the immersion depth; for acceptance criteria for samples, see 5.2.6. Note 2: For bottom-closing (top-to-bottom) type all-levels samplers, attention should be paid to whether free water exists at the bottom of the tank; some samplers are specially designed with an adjustable extension "foot" so that the closing mechanism can be actuated just above the free water.
• Routine sample (7.3.1.1.7): To obtain a routine sample by means of a bottle equipped with a weighted sampling cage (or a weighted sampling bucket), where necessary, it should be equipped with a suitable device to limit the filling rate; lower the open bucket or bottle/cage from the liquid surface to the tank bottom at a uniform rate (avoiding the bottom free water), then raise it back to the liquid surface, and when changing direction, there must be no pause; select the size of the oil-filling restriction hole and/or the raising and lowering rate so that when the bottle or bucket is removed from the liquid, it is filled to approximately 80%, but not more than 90%; immediately close the bottle stopper tightly, or carefully transfer the entire sample from the weighted sampling bucket to another carrying container (see 5.2.5). For certain routine samplers, the size of the oil-filling restriction hole should be adjusted according to the depth and viscosity of the liquid, and then the routine sample should be collected according to the operating requirements. When a fixed-volume routine sampler is withdrawn from the liquid, if it is filled to less than 90%, it may be assumed that during the passage of the sampler through the liquid in the tank, the oil flowed into the sampler from all depths; if, when the sampler is withdrawn from the liquid, the sampler is filled to above 90%, the sample may not be representative, the sample taken should be discarded, and sampling should be repeated using a smaller oil restriction hole and/or a faster raising and lowering rate. During the operation of the routine sampler, attention should be paid to whether free water is present at the bottom of the oil tank. This type of sample should generally not include free water, but the amount of free water can be specifically determined by gauging or by bottom sampling with an interface sampler.
• Tank equipped with a vapor lock valve (7.3.1.4): 7.3.1.4.1 The oil tank is equipped with a vapor lock valve, and a matching portable sampling device (PSD) should be used, or a suitable gas-tight adapter may also be used; select a suitable sampler according to the type of sample to be collected, and connect it to the suspension device of the PSD tape/cable; activate the trigger device associated with the sampling valve, and for a routine sampler or an all-level sampler, select the required oil-filling restriction device. 7.3.1.4.2 Before opening the protective cover, confirm that the vapor lock valve is fully closed; check whether the reference surface of the vapor lock valve and the matching reference surface of the PSD are clean, and remove all foreign matter that prevents the PSD from seating correctly and sealing gas. Note: This contact can usually allow the PSD to be continuously grounded through the tank body, and a separate grounding wire may also be provided for it. 7.3.1.4.3 Install the PSD onto the vapor lock valve; before connecting and tightening, ensure that the PSD is correctly seated so that it is locked in the correct position; where the PSD is equipped with a separate grounding wire, it should be connected to a suitable part on the tank body to ensure continuous grounding. 7.3.1.4.4 Fully open the vapor lock valve, and carefully lower the sampler into the tank by turning the winding handle of the PSD tape or cable in reverse; according to the type of sampler used, perform sampling by the method specified in 7.3.1.1; when retrieving the sample, the sampling device should be fully raised above the vapor lock valve before the valve is closed; after the sample is retrieved, before opening the PSD and/or transferring the sample to another container, the vapor lock valve should already be fully closed. 7.3.1.4.5 When a sample is obtained through a restricted system PSD, the sample should be handled in the same way as an open sample (see 7.3.1.1), and if necessary, transferred to another carrying container; when a sample is obtained through a closed system PSD, the sample should be completely transferred through the gas-tight PSD body into a fixed- or variable-volume carrying receiver. Note: Before reusing the restricted or closed system PSD, it is very important to inspect the cleanliness of the internal components of the PSD body (as well as the sampler).
• Pressure tank with valve sampling point (7