ISO 3170 Petroleum liquids - Manual sampling
5 Apparatus
5.1 General
All sampling devices shall be designed to be leak-tight, and constructed so as to assure the function for which they are intended in order to maintain the initial characteristics of the oil. They shall be of sufficient strength and externally protected to withstand normal internal pressures likely to be generated, and sufficiently robust to withstand any handling that may be encountered. Their cleanliness shall be confirmed before use.

NOTE 1 In some cases, it may be desirable to rinse the sample receiver/equipment with the fluid that is to be sampled, prior to taking the actual sample (although this will normally only be practicable with liquid hydrocarbons).

NOTE 2 Various sampling devices are described in 5.2 to 5.7 and any essential aspects are specified. Detailed specifications have not been given for these items because any suitable device of the type described may be used.

5.2 Tank samplers
5.2.1 General
Tank samplers are classified according to the type of sample to be drawn, these are:
spot sample,
zone/core sample,
running sample, and
all-level sample.

Tank samplers are also classified according to the mode of tank operation and sampling access, these are:
open (traditional) sampling,
restricted sampling, and
closed sampling.

Synthetic fibre cords shall not be used for lowering or raising tank samplers through the tank contents as they can generate electrostatic sparks.

NOTE Chains are not recommended for suspending samplers because earth continuity cannot be guaranteed.

5.2.2 Spot and zone samplers
5.2.2.1 General
Spot and zone samplers shall be constructed so that a sample can be taken at any specific level in a tank. The equipment described in 5.2.2.2 to 5.2.2.4 is suitable.

NOTE Other spot sampling devices are available and may be used. Some have special opening facilities, for example, having valves opened or closed at the desired level by a weight falling down alongside and guided by the suspending cable, or having wing or flap valves which are closed upon initiation of upward movement. Some are designed to be operated when deployed via a vapour-lock valve (restricted and closed system samplers).

5.2.2.2 Sampling cage
A sampling cage shall be a metal or plastics holder or cage, suitably constructed to hold the appropriate container, typically a bottle or can. The combined apparatus shall be weighted so as to sink readily in the product to be sampled, and provision shall be made to fill the container at any desired level (see Figure 2).

Sampling cages should be sized to fit the desired sample bottle size. Some designs of bottle cage can accept a variety of different neck size (and volume) bottles, and incorporate a floating ball system to seal the bottle once it has been filled.

NOTE 1 The use of a sampling bottle cage is preferred to other spot sampling methods for volatile products, since it avoids the loss of light ends that is likely to occur when transferring the sample to another container.

NOTE 2 The sampling cage may be omitted if the sample bottle is securely attached to a weighted cord. The cork is also tied to the line about 150 m from the neck of the bottle.

5.2.2.3 Weighted sampling can (beaker)
The sampling can or beaker (see Figure 3) shall be weighted so as to sink readily in the liquid to be sampled. The lowering device shall be attached to the can in such a manner that the stopper can be opened by means of a sharp jerk. In order to avoid problems in cleaning the can and/or possible contamination of sensitive samples, any weighting material shall be fixed to the can in such a way that it does not come into contact with the sample.

5.2.2.4 Zone/core sampler
A zone/core sampler shall consist of a tube made of glass, metal or plastics material, open at both ends to allow a free flow of liquid during lowering through the fluid. The closing of the lower end at the desired level may be achieved by various devices:
a) a closure mechanism actuated by upward movement of the sampler;
b) a weight falling down the suspending cable (drop messenger), so as to actuate the closure mechanism;
c) a float-operated trigger closure mechanism;
d) a closure mechanism actuated by an extension rod or by a sharp tug of the cord.

A zone/core sampler shall be designed and constructed such that, if lowered slowly, it can be used to trap a vertical column of liquid at any selected level, including the bottom of the tank. (See Figures 4 and 5.)

NOTE An interface sampler is a specific type of zone/core sampler designed to trap a vertical column of liquid at the oil/water interface at the bottom of a tank, or at any other selected level, such as the interface of oil floating on ballast water in a ship's tank, but may also be used to withdraw zone samples from any selected level within a tank (see Figure 6).

5.2.3 Bottom samplers
Bottom samplers are receptacles which can be lowered to the bottom of a tank where a valve or similar closure is opened by contact with the floor of the tank and closed on lifting (see Figure 7). Some designs of bottom samplers are available with an extendible "foot", to allow sampling just above a layer of sediment (that might otherwise prevent the leak-tight closure of the sampler).

NOTE Some designs of zone/core or interface sampler may also be used as bottom samplers.

5.2.4 Residue/deposit samplers
5.2.4.1 Deposit sampler
There are two types of deposit samplers in common use. They both rely on spring actuation of either a jaw closure device or suction device. Typical examples are shown in Figure 8.

5.2.4.2 Gravitation/ram core sampler
This is a tubular device of uniform diameter either weighted or equipped with a mechanically operated driver to penetrate the deposit layer to be sampled.

5.2.5 Running samplers
A running sampler is a container equipped with a restricted filling device that obtains a sample whilst being lowered and raised through the liquid.

NOTE 1 It has not been established that running samplers fill at a uniform rate, because
a) the tank volume may not be proportional to the depth, or
b) the operator may not be able to raise (or lower) the sampler at the variable rate required for proportionate filling which is approximately proportional to the square root of the depth of immersion.

NOTE 2 A fixed volume running sampler may be based on a sampling-bottlecage or a weighted sampling can. Proprietary fixed volume running sampler devices are also available, which may be provided with a series of selectable orifices to suit different oil depths and viscosities.

NOTE 3 Alternatively, variable volume running samplers, where the capacity of the primary sample receiver increases with the distance travelled through the tank contents, may be available. Such devices are acceptable provided that they can be shown to fill at a consistent rate during travel through the liquid.

5.2.6 All-level sampling devices
An all-level sampler is a container equipped with a restricted filling device that obtains a sample when moved through the liquid in one direction only.

NOTE 1 It has not been established that running samplers fill at a uniform rate, because
a) the tank volume may not be proportional to the depth, or
b) the operator may not be able to raise (or lower) the sampler at the variable rate required for proportionate filling which is approximately proportional to the square root of the depth of immersion.

NOTE 2 These devices may be similar to those devices used to take running samples or may be proprietary devices specifically designed to obtain this type of sample.

NOTE 3 A "bottom-up" fixed volume all-level sampler may be based on a sampling bottle/cage (or a weighted sampling can) which is lowered in the closed position to the bottom of the tank, opened, and the sample is collected as it is raised through the liquid.

NOTE 4 Proprietary "top-down" and "bottom-up" fixed volume all-level sampler devices are also available, which are provided with different opening or closing mechanisms. Additional means may be provided to restrict the inlet flow rate to suit different oil depths and viscosities. A typical example of a "top-down" fixed volume all-level sampler is illustrated in Figure 9.

NOTE 5 Alternatively, variable volume all-level samplers may be available. Such devices are acceptable provided that they can be shown to fill at a consistent rate during travel through the liquid.

5.2.7 Restricted and closed system samplers
If safety and/or environmental constraints restrict the use of open tank sampling equipment and procedures, samples may be taken using restricted or closed system samplers operated via a vapour-lock valve. Such systems are particularly suitable for use on pressurized tanks, tanks where the ullage space is inerted, and/or tanks which are part of a vapour balancing/recovery system.

Proprietary samplers are available that are designed to take spot, zone, interface, bottom, running and all-level samples under restricted and/or closed conditions. The sampler is connected to a graduated sampling tape or cable, and inserted in a portable sampling device (PSD) which is fitted with a winding mechanism. The whole assembly is then connected to the vapour-lock valve, which replaces the traditional gauging hatch used in open sampling operations. A typical example of a closed system sampler and vapour-lock valve are illustrated in Figure 10.

Restricted equipment is designed to substantially reduce the release of vapour while the vapour-lock valve is open, but has no special facilities for subsequent sample handling or transfer operations once the vapour-lock valve has been closed. Thus, there may be a small release of vapour to the atmosphere.

Closed equipment is designed to be completely gas-tight at all times, to prevent any release of vapour to the atmosphere. Portable closed sampling devices are therefore normally provided with special facilities to:
ensure gas-tight connections, and
allow sample transfer to secondary (transportation) receivers without vapour loss.

In addition, other facilities may be provided which permit:
vapours held up within the housing to be displaced back to the tank or to an absorbent canister, or the system to be purged with inert gas.

NOTE Closed system conditions do not permit the visual verification that running or all-level samples have been taken representatively in fixed volume sample receivers (i.e. that they are not completely full).

5.3 Drum and can samplers
A tube sampler is commonly used for sampling from drums and cans (see Figure 11). This is a tube made of glass, metal or plastics material, with suitable fittings if required to facilitate handling.

A tube sampler may be used to obtain spot samples or bottom samples by temporarily closing the upper opening with the thumb before inserting it into a drum or can to the desired level. When the tube is at the desired level, the thumb is removed from the upper opening, allowing the tube to fill with the sample. Once the tube is filled, the upper opening is once again closed with the thumb, allowing the sample to be withdrawn with the tube sampler. The sample is then transferred to a secondary sample receiver.

Provided that the tube has a uniform cross-sectional area throughout its length, it may also be used to obtain zone or core samples from the whole liquid height within drums or cans. These samples are taken by lowering the tube sampler slowly in the open position so that the rate of sample in-flow equals the rate of descent. Once filled, the upper opening is sealed to allow removal of the tube sampler prior to the transfer of the sample to a secondary sample receiver.

A more sophisticated design of tube sampler, having a closure mechanism at the lower end, may be used similarly for taking a representative zone or core sample.

Drum pump or siphoning devices are not recommended for volatile oils due to the risk of light-end loss. Siphoning should never be attempted by mouth.

5.4 Pipeline samplers
5.4.1 If an automatic pipeline sampler is required, this shall be in accordance with ISO 3171.

5.4.2 A manual sampler consists of a suitable pipeline probe with an isolating valve. The probe shall extend into the pipeline so that the point of sample entry is not nearer to the pipe wall than a quarter of the internal diameter. The probe entry shall face into the direction of the flow that is being sampled within the pipeline, see Figure 12.

If fixed volume sample containers (e.g. bottles) are to be filled, the probe outlet valve shall have a delivery tube that will be long enough to reach the bottom of the sample container, allowing submerged filling.

5.5 Sample receivers, vessels and containers
Fixed volume sample containers may be glass or suitable plastics bottles, metal covered bottles, or cans, depending on the product to be sampled. Depending upon application, it may be necessary for metal receivers to be lined internally with a suitable coating. Lacquer lined cans and drums may be suitable.

Variable volume sample receivers may be designed for either low pressure or high pressure applications. Low pressure designs include collapsible plastics containers, bladders, and vessels fitted with a flexible internal diaphragm. High pressure variable volume sample receivers are pressure vessels with an internal piston, which moves against a gas buffer as the sample is accumulated against the other side of the piston. A typical example of a high pressure variable volume sample receiver (a floating piston cylinder) is illustrated in Figure 13.

NOTE Some designs of high pressure variable volume receivers have two pistons, which enable the sample to be mixed within the receiver (prior to subsampling) by repeatedly forcing it through a central mixing device (Figure 14).

Before use, variable volume sample receivers are normally collapsed, evacuated or reduced to the nominal zero volume (by filling the opposite side of the diaphragm or piston with inert gas). The sample volume expands as the sample is accumulated, either by compressing the inert gas or by cautiously reducing the inert gas pressure.

The sample receiver/container size is dependent on the quantity required for analysis (and/or retention).

Prior to any use, it may be appropriate to rinse the sample receivers, vessels and containers with the fluid that is to be sampled, in order to avoid contamination of the current samples with any residue from previous samples and/or solvents used to clean the receivers.

Wherever possible, the sample should be transported to the laboratory in the vessel it was originally obtained in (the primary sample receiver), and therefore the methods which do not require sample transfer to a secondary vessel should be preferred.

Plastics containers shall not be used for long-term sample storage unless it has been demonstrated that the plastic is suitable (i.e. compatible with the sample) so that the integrity of the sample is not compromised. The use of containers made of non-linear polyethylene may lead to sample contamination and/or sample container failure.

5.6 Container closures
Corks, or plastics or metal screw-caps may be used for closing fixed volume sample receivers/containers. Natural rubber stoppers shall not be used. Corks shall be of good quality and free from loose pieces or dust. They shall be softened by rolling or squeezing, and pressed well into the neck of the bottle to prevent leakage or evaporation. Where necessary, a protective cover of a suitable material shall be used.

Screw caps with compressible sealing inserts are recommended in preference to corks, when sampling volatile liquids.

Corks shall not be re-used for different types of product, since thorough cleaning is difficult and hydrocarbons may penetrate into the cork and cause contamination of subsequent samples. Re-use of corks is not recommended, but is permissible if the use is restricted to one type of product.

Screw-caps of cans or bottles shall be fitted with discs of cork faced with oil-resistant material, or a compressible plastics sealing insert. Cork discs shall only be used once. They shall be removed before the cleaning of screw-caps and replaced with a new disc prior to the cap being re-used.

Similar closures may be used with low pressure variable volume sample receivers, but high pressure variable volume receivers shall be fitted with suitable valves. Additional blanking cover caps may be provided to seal the valve connection points of high pressure receivers prior to their transportation between the sampling location and the laboratory.

5.7 Sample coolers
A cooling coil made of seamless copper tubing, or other suitable metal tubing, with an appropriate internal diameter, shall be fixed in an open, portable container in such a way that it is immersed in a water or water/ice mixture during use. The cooling coil alternatively shall be fixed within a closed container through which a cooling fluid is circulated.

The inlet end of the tubing shall be furnished with a flange or other appropriate means of connection to the sampling valve. The outlet end shall be open.

Sample coolers shall be efficiently flushed before collecting the cooled sample.

Care is required to ensure that the use of a sample cooler is appropriate (see 7.2.3.2).