ISO 3171 Petroleum liquids - Automatic pipeline sampling
11 Sample receivers and containers
11.1 Sample receiver
The sample receiver should be equipped with a level indicator or equivalent device, for example a weighing system, for monitoring purposes, and a high-level shut-off or alarm device.
Means should be provided to mix the contents of the receiver to ensure that representative samples are transferred into laboratory apparatus or other containers.
Two types of sample receiver are in current use.
11.1.1 Sample receivers - fixed volume
These are receivers with a fixed volume into which the sample is admitted so that it contacts the enclosed atmosphere.
11.1.2 Sample receivers - variable volume
These are designed to avoid contact between the crude oil and air, thus preventing possible loss of light ends and water vapour. They may be made of a suitable flexible material so that they are fully collapsible or they may consist of a container with a piston or diaphragm precharged with nitrogen or helium. The latter are particularly applicable to liquid petroleum products with high vapour pressure, and to crude oils.
11.2 Sample container
The sample container may be equipped with an internal homogenizer or with the necessary connections for an external mixing system (see 12.2.3).
11.3 Common characteristics of sample receivers and containers
11.3.1 Fixed-volume receivers should be constructed to provide sufficient space for ullage to remain at the end of the sampling period, and a means of relieving any increase in pressure due to expansion under all conditions. The design of the vessel should be such that any expansion due to heating of the contents to the highest temperature to which the vessel might be subjected will not cause the working pressure to be exceeded.
The vessel should be made of petroleum-resistant material. It should be noted that receivers or containers made of a plastics material may not be suitable for long-term storage of samples because permeability of the plastics may result in differential loss of some of the components of the sample.
The vessel should be capable of being vented through a pressure control valve with an appropriate setting to minimize the loss of low-boiling-point components.
11.3.2 Pressure tests and other inspection work should be performed according to the local regulations. Cleaning and leak testing should be performed at regular intervals.
11.3.3 The design and material of construction should be such that the internal surfaces in contact with the liquid are smooth and of a finish which will inhibit the retention of water when the contents are transferred or removed for analysis. The design should be such that they tan be easily cleaned.
11.3.4 The necessary connections should be fitted to permit sample transfer from the receiver to the container, and from the container to the laboratory apparatus, without contamination or loss.
All connections should be fitted with blanking plugs or end taps, except for the relief valves. Gauge glass and drain valve internal lips should be avoided. Dead legs are not permitted.
If necessary, the sample receiver and its connections should be thermally lagged and/or heat traced to prevent solidification of the sample and facilitate drainage (see 8.4).
11.3.5 The volume of the sample required for analysis and for retention as a reference should meet the requirements of the particular application. Furthermore the local or national fiscal authority may require a minimum quantity of sample to be taken.
This will determine the minimum size of the sample receiver(s) and container(s). The duration of the sampling period, the grab size, the sampling frequency and the requirements for adequate mixing (homogenization) are also relevant considerations in determining the receiver size.
If the total sample is contained in more than one receiver or container, great care should be taken to account for differing volumes in each receiver or container filled successively when either recombining the results of analysis, for example for the average water content of the whole sample volume, or in the preparation of composite samples for other analysis if required.
11.4 Sample labelling
11.4.1 Sample containers should be labelled. Oil-resistant tie-on or wire-on labels are preferred and these should be permanently marked.
11.4.2 It is recommended that the following information be provided on the label:
a) place at which sample was drawn;
b) date and time sampling commenced;
c) date and time sampling was completed;
d) Sample tag number or identification number of the container;
e) type of liquid being sampled;
f) quantity of liquid represented by the sample;
g) tank number and type, name of ship, flowline reference, etc.;
h) destination of sample;
i) signature of person responsible for collecting sample.