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Survey Documentation 

Open Measurement

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Survey Documentation - Open Measurement Equipment and Procedures

Open measurement occurs whenever a vessel's measurement hatch is opened to the atmosphere to perform the necessary measurement tasks. The equipment needed and procedures to be used to perform open measurements on ships and barges are described in this section.

Open Manual Sampling. This section describes the equipment to be used to take a manual sample.  For details about sampling procedures and handling of samples see Section 7 of this document.

Open Sampling Equipment - General

Sampling equipment must be in good condition, safe, and be made of such material that no interaction between the container and the cargo would affect the integrity of either.

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Additional consideration should be given as to how the sample will be used. Each device should be used in the manner prescribed by its manufacturer. 

Additional technical data on open manual sampling equipment, is available in API MPMS Chapter 8.1. - Thief SamplerLiquid Petroleum-Open Sampling Equipment

There are several containers (receivers) which are used to sample cargo. The most common types currently in use are the weighted glass bottle, beaker thief, and zone sampler.  When the weighted glass bottle method is used, each sample can be stored in the bottle it was taken in.  This minimizes the risk of loss of light ends and accidental introduction of water.

The use of a beaker or thief to obtain a tank sample may run the risk of loss of quality of the sample through contamination, loss of light ends, introduction of water, etc.  This potential risk results from the need to transfer the sample from the beaker to another container for transportation to the laboratory.  During the transfer from the beaker, light ends will be lost and outside moisture may be introduced. In addition, the use of the same beaker to sample more than one tank may cause a contaminant to be introduced to an otherwise uncontaminated sample.

 Free Water-Open Sampling Equipment

As with cargo sampling, there are several containers that can be used to sample free water at the bottom of vessel tanks with the most common being a bottom sampler (tube container), glass bottle, or thief.

If the free water level is higher than 1 foot, a weighted bottle can be used.  Otherwise, a bottom sampler or thief must be used.  Bottom or thief samplers are usually used to sample free water under a cargo.  A typical bottom sampler has a projecting stem on a valve rod that opens two valves automatically as the stem strikes the bottom of the tank.  The sample enters the container through the bottom valve, and air is simultaneously released through the top valve.  The valves snap shut when the sampler is lifted

Sediment-Open Sampling Equipment A scoop sampler is used to sample sediment on the bottom of vessel tanks that is not covered by a liquid

Sample Containers

Containers used for samples taken from vessel tanks are usually clear or brown glass bottles, plastic bottles, or metal cans.  The only cans that may be used are those with seams soldered on the can's exterior surface with a flux of rosin cleaned in a suitable solvent.

If the cargo sample is sensitive to light, brown bottles should be used.  To minimize the loss of light ends, appropriate high-quality, clean, cork or glass stoppers, bungs, or screw caps should be used to seal sample container.  Rubber stoppers should never be used.

It may be noted that the manufacturer should be consulted if there is any question about the acceptability of the construction or type of material of a container or cap.

Inspection of Sampling Equipment

Before use, all sampling equipment (including containers and cords or chains) shall be inspected to ensure that they are clean, dry, and free from all substances that might contaminate the sample.  The use of dirty sample cords or tapes should be avoided because of the possibility of a sample being contaminated.  In addition, certain cargoes may require special precautions to be taken when preparing sampling equipment (i.e., nitrogen purging of sample containers to assure dryness).  The principals involved should be consulted if there are any questions as any special requirements necessary.

Sections of text taken from API - MPMS Chapter 17 Marine Measurement

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