ISO 3170 Petroleum liquids - Manual sampling
8 Procedures for crude oils and other non-homogeneous petroleum liquids
8.1 General
If available, automatic pipeline sampling as specified in ISO 3171 shall be used for sampling crude oil and non-homogeneous oils in preference to the following manual procedures. The automatic pipeline sampling procedure is applicable to crude oils and other non-homogeneous oils such as so-called "heavy crude oils" and residual fuels because such systems will normally include a mixing device immediately upstream of the sampler, so that the line contents are uniformly dispersed prior to sampling. The sample will also normally be accumulated flow-proportionally, to allow for any changes in flow rate while sampling throughout a batch transfer.

NOTE The manual sampling methods specified in Clause 7 may not provide representative samples for the following reasons.
a) The concentration of dispersed water in the oil is generally higher near the bottom of a tank. A running or all-level sample, or a composite sample of the upper, middle and lower samples may not provide a sample representative of the concentration of all the dispersed water present.
b) The interface between oil and free water may be difficult to locate, especially in the presence of emulsions, layers or water-bearing sediments.
c) The free water level may vary across the tank bottom surface. The bottom may be covered by pools of free water or water/oil emulsion impounded by layers of sediments or wax.
d) Light ends may be lost easily in manual operations, affecting the density and vapour pressure of the sample.

Because circumstances will arise where manual methods of sampling have to be employed, procedures are given in this clause which shall be followed so that a sample may be drawn, which is as representative of the bulk as the techniques allow. The procedures specified are additional to or replace those specified in Clause 7.

8.2 Procedures
8.2.1 Tank sampling
For tank sampling, use one of the following techniques specified in 7.3:
spot sampling;
running sampling;
all-level sampling.

By agreement of all parties, composite spot or zone samples may be prepared, see 7.3.1.2.

Where it is necessary to assess the level of stratification within a tank's contents, draw samples initially from the upper, middle and lower (or suction) levels, transport them to the laboratory or testing location and test them individually for density, water and sediment content.

If the range of the results of these tests lie within +/- 1 kg/m3 (density) and +/- 0.1 % (V/V) (water content), the tank contents shall be considered as representative of the bulk, and the average results shall be taken.

If the range of the results of these tests does not lie within the specified limits, the tank contents are probably stratified. In these circumstances, additional spot samples shall, if possible, be taken at intervening or equidistant levels, and all the individual test results averaged. For this purpose, the samples for density, water, and sediment analysis shall not be physically composited, but the results of analyses on the separate samples may be mathematically composited.

NOTE In small leased automatic custody transfer (LACT) crude oil tanks of less than 159 m3 (1000 barrels), a single spot sample from the middle of the oil is usually sufficient.

8.2.2 Pipeline sampling
8.2.2.1 General
For pipeline sampling of batch transfer quantities, use the procedures described in ISO 3171.

NOTE If it is required to take manual spot samples from pipelines, the procedure will be dependent on whether a fixed volume or variable volume sample receiver is to be used, and on the vapour pressure of the liquid that is to be sampled.

8.2.2.2 Pipeline sampling of low vapour pressure liquids
Fixed volume sample receivers shall be filled directly after thoroughly flushing the sample probe and line. Sample collection shall be by submerged delivery to minimize any risk of the evaporative loss of light end components (5.4.2). A sample cooler may be used if appropriate (5.7).

Low pressure variable volume sample receivers (e.g. collapsible flexible containers, bladders or diaphragm receivers) shall be emptied prior to use. Where appropriate, the receiver may be evacuated. The receiver shall be filled directly after thoroughly flushing the sample probe and line.

8.2.2.3 Pipeline sampling of high vapour pressure liquids
High pressure variable volume sample receivers (e.g. floating piston cylinders) shall be filled in accordance with the procedures detailed in 7.4.3.1 or 7.4.3.2. High pressure fixed volume sample receivers shall be filled in accordance with the procedures detailed in 7.4.3.3.

NOTE It will not normally be appropriate to use low pressure variable volume receivers (e.g. collapsible flexible containers, bladders or diaphragm receivers), or low pressure fixed volume receivers (e.g. bottles or cans) for sampling high vapour pressure pipeline liquids. If such receivers are used, phase separation may occur as the pressure is reduced and light-end components may be lost.

8.2.3 Additional precautions
Give particular attention to the precautions referred to in respect of the following:
a) high pour-point oils (see 7.2.4);
b) volatile oils (see 7.2.3);
c) collection of large-volume samples (see 7.2.1.8);
d) ullage to be left in fixed volume sample containers (see 7.2.1.6);
e) samples for transportation (see 7.2.5 and 8.2.4).

8.2.4 Sample transportation
Transport the samples to the test laboratory in the original sample container, without transfer or compositing (bulking), in order to maintain the integrity of the sample. If it is impossible to transport the sample in the original container, transfer it to a suitable secondary container following the procedure specified in 9.4 and record the transfer. Samples should be transported to the testing location as soon as possible, or stored in an appropriate cool, dark, dry location.

Fixed volume sample receivers/containers should be transported and stored in an inverted position, if feasible, so that any loss of vapour from the ullage space is prevented, and any leakage is immediately apparent.