Precaution/attention & record sheets are necessary for cargoes that need:
- Cargo heating : Cargoes that require heating must be monitored at least once daily
and a temperature log must be kept. Ensure that correct heating medium is used, and
that heating coils in tanks that do not require heating are blown dry and blanked. Prior to
loading heated cargo, heating coils should be pressure tested and results recorded in the
log book.
- Cargo cooling : In specialised cases, is required to prevent products from giving-off toxic and flammable
vapours.
Special care requirements are generally documented in the condition of carriage details contained in
the ships Certificate of Fitness and also in the IBC/BCH Codes. The Company and Charterers are to be consulted if additional information is required.
- Tank Atmosphere ?monitoring and recording of the ullage space of pressure and/or oxygen
should be carried out at regular intervals (daily) to ensure that the correct environment is
being maintained.
- Temperature Control : Cargoes that may self-react must be monitored on a daily basis for
any increase temperature that deviates from the ambient climatic conditions.
- Nitrogen cover : Prior sailing the vessel must have sufficient Nitrogen of the correct quality
on
board to comply with the padding requirements.
No of bottle = Total Ullage Space (m3) x 0.2 / 180` x 50, for 4 changes maintaining 50mb,
N2 bottle = 50l x 180bar
- Tank atmosphere : O2 content strictly controlled :Some cargoes like Hexane-HMD-Octene do have a maximum requirement with respect to oxygen
in the vapour space. The vapour space has to be checked with the appropriate oxygen
meter. The Shipper determines the frequency of the routine checks. The results are to be recorded
in ‘Voyage Log?
- Agitation/ Circulation : Some chemicals, e.g. Phosphoric Acid, require agitation to prevent sediment separation and
different temperature/density layers from forming. Re-circulating through a diffuser is one
method of agitating the cargo
Avoiding claimsOn many occasions cargo losses may occure during voyage and resulting in claims to the owners. Shipboard losses can be attributed to
1. Evaporation via PV vents.
2. Excessive ROB due to high pour-point of cargo or pumping problems.
While in some trades the discharge port out turn figures alone determine the amount of cargo delivered, in others they are still compared to the bill of lading figures provided by the load port.
Virtual losses (On paper only): In many shortage claims no actual loss has taken place but the amount of cargo has been overstated when loading and/or understated when discharging.
Stowing volatile cargo next to heated cargo causes evaporation losses. Charterers should specify maximum adjacent temperatures. Adjacent heat is an important spec on chemical tankers.
Chief Officer must find out that number of shore tanks to be loaded from, the quantity, temperature and SG of cargo in each. Whether there are any planned loading stops for shore tank changes. Whether density is being expressed ‘in air?or ‘in vacuum?Whether shore pipelines are full or empty, and details of any pipeline displacements planned. Whether loading by gravity or shore pumps.
Good Practices
The inspector must be accompanied at all times and his ullage measurements actively verified. Frequently maintaining and checking ship’s equipment - and arranging for yearly calibration of
electronic measuring devices by an agent approved by the manufacturer.
Never permit the use of the terminal’s measuring equipment on board. If measurements taken with the inspector’s equipment differ from those taken with the ships, propose that all measurements be taken with each, and both be sent for verification ashore afterwards.
If the ship is pitching or rolling, five measurements should be taken, withdrawing the tape as soon as it penetrates the surface of the cargo. The highest and lowest should be ignored and the middle three averaged. Weather and sea conditions should be logged.
Cargo temperature may vary by 5 °C at different levels in the tank, so must be averaged from at least three readings -top, middle and bottom. Some digital probes can measure at more frequent intervals .Measurement error of 1°C can distort the volume calculation substantially , however this will depend on cargo density also.
Reference publications:
- International Safety Guide for Oil Tankers and Terminals (ISGOTT)
- Certificate of Fitness for the Carriage of Dangerous Chemicals in Bulk
- Ship’s “Procedure and Arrangements Manual?(Approved by Class)
- BCH/IBC Code
- ICS CTSG
Related Info:
What is putrefaction process of liquid chemicals ? Most animal and vegetable oils undergo decomposition over time, a natural process known as putrefaction (going off), that generates obnoxious and toxic vapours and depletes the oxygen in the tank. Tanks that have contained such products must be carefully ventilated and the atmosphere tested prior to tank entry .
.....
Carriage of inhibited flammable chemical products in cargo tanks
In certain conditions of heat, pressure and in the presence of Oxygen, some chemical cargo types can become viscous and possibly solid and dense in nature. This self reaction can cause some cargoes , especially in the presence of high temperatures and Oxygen, to begin an exothermic reaction, becoming self heating and rapidly expanding which may result in possibly disastrous consequences for the vessel.
Cargo sampling safety precautionsCargo 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.
.....
Cargo segregation requirement for chemical tankers
In the case of two or more liquid chemical cargoes which react with one another in a hazardous manner, segregation must be done The product data sheets, together with the BCH/IBC Codes are to be studies carefully to determine the compatibility restrictions when carrying different groups of cargoes.
How to avoid solidification in cargo tanks ?
Solidification in the cargo tanks can occur when solidifying cargoes are stowed adjacent to “cold cargoes” or cold ballast water in adjacent spaces.
Cargo compatibility and reactivity of various chemical cargo
Transporting of dangerous and noxious liquid chemicals in bulk involved various risk factors.
Between some chemicals violent reactions may occur if the chemicals are mixed in certain proportions. The result may possibly be an eruption and
tank rupture. Such an occurrance must be prevented. Water may also have to be considered in this respect.
Determining presence of contaminants
in chemical cargo
To maintain product quality onboard modern chemical tankers any contaminants in the cargo need to be observed. Following guideline may be useful determining various product contaminants in noxious liquid chemicals.
Cargo compatibility chart for handling dangerous liquid chemicals in bulk
The following procedure explains how the compatibility chart should be used to find compatibility information:
.....
Ship shore cargo connection safe method
Venting of cargo tanks safety procedure
Ship to ship transfer operation
Ship shore safety checklist while alongside a terminal
Cargo compatibility chart for handling dangerous liquid chemicals in bulk
Cargo handling safe practice for chemical products
Risk with noxious liquid cargo contact
How take a sample of noxious liquid cargo ?
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