Chemical Tanker solutions reports of the sampling of dangerous & noxious liquid cargo onboard chemical tankers.
Why cargo sampling?
Cargo samples are evidence of the condition of the product during the various phases of transport (storage at terminal, arriving on board, loading, passage, discharging). This procedure describes sample-taking procedures and the legal background. Suitable PPE is to be worn when taking samples. Sample bottle to be flushed prior collecting sample.
For protection against possible cargo claims it is very important that cargo sampling is correctly carried out. The following is normally required ;
- Manifold, 1st foot and completion of loading sample for each tank
Manifold, tank sample prior discharging - Cargo sample register to be maintained
- All samples to be sealed and sampling to be witnessed by ship staff
- Cargo samples are to be retained onboard for a maximum of 12 months, thereafter disposed off ashore and record maintained
- In case of cargo quality dispute, retain ship samples carefully
- Ensure sample bottles, sample lines and closed sampling cans are completely clean prior collecting samples. Contaminated ropes will contaminate samples.
- Depending on the cargo involved, a series of samples are taken to determine the ship’s preparedness for loading. Always accompany surveyor during sampling.
How many samples are taken depends on the conditions in the charter party and the type of cargo. Unless specified otherwise, as a general rule a sealed sample should be taken for every tank carrying cargo. Samples taken by the vessel bearing no signature from the surveyor or other authorised person, unless a very good documented sample log is kept by the vessel, have no real value as evidence in legal actions.
Samples must be taken at the manifold where it is permitted, prior to releasing cargo to the tanks to ensure that Shore lines are clean and correct cargo being loaded. Whenever more than one tank is to be loaded with the same cargo, cargo is to be loaded one by one line/tank at a time to avoid contamination of whole cargo system when loading 1st foot.
After examination of the tanks, mudboxes, piping etc (as far as possible) for cleanliness it is usual to load sensitive chemicals into the ship’s tanks to a level of approximately 0, 3 m and then take samples from the tanks, presuming that any previous residues in the piping are by then dissolved into the new cargo (”soak test”). Similarly samples are taken from an initial discharge into container tanks or similar located on the shore before commencing unloading at full rate to the shore storage tanks.
If a “soak test” upon loading is turned down by the surveyor or the shipper and loading stopped, the chief officer should then request sealed and identified samples of the cargo lot in question, from the ship’s tanks as well as from the shore tanks. By these means the shipowner may be able to protect his interests in case of any dispute.
Sometimes drip-samples are taken from the loading manifold during loading. This method is simple, but not always fully representative. The pumping rate may vary during the transfer, whilst the sampling rate is more or less constant. Furthermore it is difficult to guarantee the proper identity of a sample taken over a long period of time. This is not meant to discourage the ship’s officers from taking a drip-sample during loading, but only to mention the weak points of the method. In fact, drip-sample during loading may be the only way to establish whether a cargo was contaminated during the pumping on board or ashore.
Before unloading cargo samples are normally taken from the ship’s tanks. The cargo samples should be sealed and marked on board, particularly if no independent surveyor is present. The ship should keep one sample for future reference in case of any disputes arising. The samples should be stored in a dark and cool room especially put aside for this purpose. The room should have steel bulkheads and be open to the weather deck.
Samples of products which deteriorate or change with, time (e g styrene, vegetable oils) have a limited purposeful storage time on board. With e g phosphoric acid the samples may remain representative as regards chemical composition, but may not be so as regards contents of sediments, However, normally the samples are stored one year, which is the normal respite for making any claim.
Sampling at deep levels is carried out with containers which are lowered upside down or have valves or other means of filling themselves up at the deeper level. Sampling at various different levels is necessary for products which have a tendency to stratify, viz phosphoric acid which may contain a higher percentage of solids near the tank bottom than at top level.
Safety precautions
Sampling is risky, vapours or spray from the product may cause poisoning, caustic burns or scalding of personnel. Release of small amounts of products may also cause problems on deck or the environment (terminal, water). For these reasons, it is absolutely necessary to comply with the strictest safety regulations and the requirements of the material safety data sheets.
When samples are taken through tank openings (hatches), personnel should stay to the windward side of the opening. Depending on the properties of the cargo, suitable protective clothing should be worn as required. When taking samples from lines under pressure the risk of spray from the product should be taken into account.
Closed sampling to be carried out whenever possible except at manifold.
Sampling should not take place until 30 minutes after loading has been completed to ensure any static charges have been dissipated. Earthing requirements of the instrument must always be complied with, as per the manufacturer’s instructions. The bonding connection must be tested by ship staff prior to each cargo operation and if any abnormalities are found, the instrument is to be withdrawn from service until rectified.
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Source: Chemical Tanker Solutions
