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Cargo planning guideline for modern chemical tankers

Chemical data sheet means a document, in accordance with the IMO Codes and usually from the manufacturer of the cargo, (Cargo Information Form) that contains necessary information about the properties of the chemical for its safe carriage as cargo. Careful study of such data sheets are essential in cargo planning of various chemical cargo , safe stowage and any segregation requirement etc.

Every chemical tanker must have a Procedure and Arrangements Manual that gives Procedures for compliance with Marpol Annex II when noxious liquid substance cargoes are handled on board. The following sequence outlines a general cycle of operations, and supplementary comments are made where relevant.

Outlined below some needful guidance for handling various noxious liquids . Should be considered as general guidance only, as there are considerable variation in the design of cargo containment and cargo handling systems. Specific instructions in the form of Critical Operations Checklists should be prepared for individual vessels.

The cargo containment and handling systems have been designed and constructed in accordance with the requirements of the IBC/BCH codes, the SOLAS convention and the MARPOL 73/78 convention to safely transport and handle the chemicals the ship is certified to carry.
Tanker at sea
Fig: Modern Chemical tanker underway

However, the required levels of safety in cargo-operations can only be achieved if all parts of systems and equipment are maintained in good working order. Similarly, the personnel involved in cargo operations must be fully aware of these instructions, their duties and be thoroughly trained in the correct procedures and handling of the equipment.

Before and during all operations involving the cargo, ballast and bunkering systems, the Master must ensure that the precautions required by the company safety management system and relevant checklists are fully observed.

Reference is to be made to the publications listed bottom of this page as well as equipment operating and instruction manuals.

Each vessel, which is certified for the carriage of noxious liquid substances (NLS) in bulk, is provided with a Procedure and Arrangements Manual (P & A Manual). All substances permissible for carriage onboard are listed in this manual and are approved for and on behalf of the flag state government that the vessel is registered under, usually by a Classification Society acting on its behalf.

The purpose of this Manual is to identify the arrangements and equipment to enable compliance with Annex II of MARPOL 73/78 and to identify for the ship’s officers all operational procedures with respect to cargo handling, tank cleaning, slops handling, residue discharging, ballasting and deballasting, which must be strictly followed.

If the vessel has been nominated to load a cargo that is not listed in the P&A Manual, this should be notified to the vessel's operator. They will then liaise with the Class Society to determine whether a note of acceptance or a dispensation is possible for this cargo.

The details of permissible substances for carriage onboard are detailed in an attachment to the `Certificate of Fitness', which is also issued by the flag state and usually delegated to a Classification Society acting on its behalf.

The P&A Manual must be updated as necessary to reflect any changes to the vessel’s structure; tank coatings etc and any alterations to the Manual are to be Class approved.

A check list is given below, which might be useful when discussing cargo planning in your ship.

1) Load the vessel so that positive trim is ensured during discharge, preferably without filling ballast in cargo tanks, particularly not in port. Try to find out the receiver's desired sequence of discharge. Keep an eye on hogging /sagging!

2) Inter-reactive cargoes must not be placed in neighbouring tanks. Piping systems must be separated by double blind flanges to prevent erroneous handling of valves. Check the cargoes for cargo compatibility.

3) Toxic cargoes must not be placed in neighbouring tanks with edible products (human or cattle). Separate the piping systems by means of double blind flanges

4) Check with the tank coating manufacturer's list of permissible cargoes for coatings in each tank. The general rules are: Zinc silicate coatings are resistant to strong solvents (aromatics, alcohols, ketones etc). Zinc silicates are not resistant to caustic soda or alkaline cleaning chemicals.

Epoxy coatings are resistant to petroleum products, caustic soda, vegetable oils, wine, seawater, fatty acids, limited resistance to alcohols and aromatics.

Coal tar epoxy is resistant to sea water, crude oil and petroleum products in general but should not be used for jet fuels or light oils as they tend to be contaminated by bleeding tar.

5) In certain cases the tank coating manufacturer gives a limited acceptance for a product (time and/or temperature). Avoid then placing heated products on the otherside of the bulkhead. Let epoxy weather out properly after solvent cargoes. Do not fill ballast water immediately after methanol in the same tank.

6) Polymerizable products (e g styrene, vinyl chloride) should never come in bulkhead contact with heated cargoes. The same refers to drying vegetable oils (e g linseed oil) .

7) Volatile products (aromatics, ketones, alcohols etc) should not be put into bulkhead contact with heated cargoes in order to avoid unnecessary evaporation losses.

8) The cargo tanks are normally inspected and approved prior to loading. This does not necessarily relieve the vessel of responsibility for contaminations. The master/ owner carries the responsibility in taking due care of the cargo. To protect ones own interest the vessel's own inspections should be recorded in the deck log.

9) After cargoes with a strong odour (fish oil, phenol, octanol, tall oil, turpentene, molasses) the tanks should not be used immediately for odoursensitive cargoes such as glycols, ve getable oils,

10) After leaded gasoline, cargoes for human or animal consumption must not be loaded as the next cargo, neither "virgin naphta feedstock". Lead compounds may adhere to the bulkheads after several intermediate cargoes even in coated tanks. Wine cargo may dissolve lead remains, which are many intermediate cargoes ''old".

11) In case of doubt of purity of cargo to be loaded: take cargo samples also from the loading manifold upon loading and have them sealed and identified for future reference.

12) In tanks which have contained products with a high boiling point and/or low water solubility (e g lubrication oils) there will be minute amounts of cargo left after washing. These tanks are then not suitable for a ''sensitive" cargo such as methanol.

13) Consult the cargo trim and stability book. There may be restrictions with regard to cargo distribution and stabllity in hypothetical damaged condition.

14) When one and the same pipe has to be used for several consecutive products: Start with the lighter products, going on to more viscous ones. The pipe may have to be drained and steamed in between, therefore try to arrange an open loop. The most sensitive cargoes may have to be loaded "over top" through the hatch.

It should be borne in mind that individual ship has got own characteristics and limitations may involved handling various chemical cargoes . The master and all personnel in all cases must be aware of cargo/ship information that has been given and comply with relevant safety procedures.

The following reference publications provide useful information while planning cargo:

Related Info:

Voyage planning and related considerations
Prior commencement of a voyage a ship master is by law and in practice ultimately responsible for the correct stowage of the cargo. He must take all parameters such as, but not limited to, the following when deciding on which tanks to use for the stowage of a particular cargo; ....

How to prepare a cargo loading or discharge program ?
For quick reference throughout the cargo operations onboard chemical tanker it is responsibility of ships chief officer to prepare a loading/discharge programme , which is to include, but not be limited to, the following (note additional information can be appended): ....

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