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Liquid Chemical Cargoes Loading Plan- Tank Cleaning Special Considerations

A wide range of liquid chemical cargoes is transported in bulk by purpose-built tankers. Such cargoes can be broadly categorised as (a) chemicals which are liquid at ambient conditions and (b) those which are gases under ambient conditions but are liquefied for bulk shipment by the application of high pressure or low temperature.

These commodities generally undergo processing in the chemical industry that may involve expensive and sensitive catalysts which are susceptible to irreversible damage by contaminants in the feedstock. Consequently, most chemical commodities are manufactured to a high level of purity and require very careful handling during loading, carriage and discharge to ensure that the product remains in perfect condition at out-turn.

chemical tanker navigation at sea
Prior shipment of liquid chemicals the importance of proper tank cleaning procedures and the correct preparation of tanks and all related equipment cannot be overemphasized. Masters may wish to consider appointing an independent surveyor to verify the condition of the tank coating, heating coils and hatch openings after the tank preparations have been completed.

The specific cleaning method will depend on the previous cargo carried and the cleanliness needed for the load to be stored. The appropriate tank cleaning guides should always be discussed. Generally, an essential part of the tank cleaning process is Butterworthing with hot or cold seawater at adequate pressure and the proper tank levels. It should be accompanied by a freshwater wash to remove seawater deposits. Tanks that may have carried monomer or drying oils should first be washed with enough cold water quantities to avoid cargo residues' polymerization. It is vital to apply tank cleaning chemicals in some cases, but their use is generally restrained as it may be difficult to dispose of slops.

In the end, the tanks should be clean, dry, and free from residual odors. It may also be beneficial to take wall-wash samples and analyze previous cargoes' traces, although this requires skilled inspectors. The presence of smell in a tank that has been cleaned intimates cargo trash and suggests the need for further cleaning. When checking for remaining odors, it is prudent to conduct the test after the tank has been closed. Testing should, in any case, be taken out by staff who have not been operating in or adjacent the tanks for at least one hour.

When load with a high melting point has been carried, tanks should be rinsed with hot water. If possible, steam should be utilized to ensure the residues are efficiently melted and cleared. The cleaning process must also incorporate the tank lines, tank lids, and vent lines, including pressure vacuum valves and risers. Examples of liquid with high melting points include phenol and waxes.

Cargo pumps, generally of the hydraulic deep well type, should be disassembled and inspected as recommended by the maker. The pumps should be purged to examine the seals that group the cargo and hydraulic oil from the pump's void space. This method should always be succeeded after tank cleaning, before loading and discharging, and after repairs. The results should still be appropriately recorded in the ship's logbook or other approved records. Where defects to the seals are presumed, cargo should not be worked until corrective actions have been taken. When cleaning pumps, consideration must be given to the ship's trim to ensure that any contaminated shipment is adequately dissipated away. Transportable pumps should be examined before being lowered into the cargo tank.

If heating coils are not to be utilized, they should be purged entirely and blanked both at the supply, and the return ends before loading commences. Even though coils may have been in practice for some time, they should be pressure tested before loading to avoid contamination through leaks that might have incurred. Pumps not needed for cargo operation should always be separated.

Particular attention should be paid to vent lines' cleanliness, as they may comprise residues of past load, both in a fluid and a solidified state. When not cleaned after discharge, Vent lines may drain into a recently loaded tank when the ship changes trim or when encountering adverse weather. Hardened cargo deposits in a vent line may melt due to the heat released from a heated load, and the melted stock may flow back into the tank, causing contamination. The usage of steaming vent lines after the carriage of heated cargoes is justified, as blocked lines may result in the overpressuring of cargo tanks.

Drain cocks provided at the lowest parts of the deck, and manifold lines and plugs at the bottom of cargo valves should be opened and rinsed to remove any trapped cargo residues. These drain cocks may contain sufficient liquid to result in severe contamination. When clearing deck and drop lines, it is essential to ensure that these lines' dead ends and drop lines are not overlooked. They should be opened and thoroughly cleaned.

Mild steel tanks are sometimes used for the carriage of natural oils and fats, but their use is in decline as cargo charterers more frequently stipulate stainless steel or coated tanks. When used, mild steel tanks should be free from rust and scale, since remnants of previous cargoes are likely to be trapped and transferred into subsequently loaded shipments. Where sensitive cargoes have been carried in mild steel tanks, contamination has been known to occur from the residues of hydrocarbon (petroleum products) cargoes.

Upon completion of loading, an independent surveyor's ullage survey may be appropriate, and after that, valves and hatches should be sealed. This process can be repeated at the discharge port. Taking onboard samples at all stages of the loading and discharging operation is also highly recommended.

Should contamination happen at some stage in transportation, it may be possible, by analysis of such samples, to identify the origin of the problem. By ensuring that the cargo is carried to the highest standards, the stock should be well protected.

Cargo Loading plan- special considerations

Careful planning prior to loading is obviously essential and the following key points are amongst those that should be considered.
  • Tank Capacity: ascertain that there is sufficient volumetric capacity including an allowance for expansion of the cargo due to an increase in temperature.
  • Tank Coating: ensure that the integrity of the tank coating is suitable for the safe carriage of the particular commodity.
  • Adjacent Cargoes: ensure that the commodity to be loaded is compatible with cargo in adjacent tanks. If an adjacent cargo is heated, check that the cargo to be loaded will not be adversely affected.
  • Temperature Control: if the cargo is to be temperature controlled, load it in a tank capable of performing the task and test the heating/cooling system prior to loading the cargo.
  • Tank Cleanliness: ensure that tank cleanliness is appropriate and adequate for the cargo to be loaded.
  • Loading/Discharge Plan: ensure that at all stages of the loading and subsequent discharge of cargo parcels, trim and stability will be within acceptable operating limits.

Cargo Plan, Stowage Plan – A plan showing the distribution of all cargo parcels stored on board of a vessel for a voyage. Each entry on the plan details the quantity, weight and port of discharge. A plan presenting the quantities and description of the various grades carried in the ship cargo tanks after the loading is completed.

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):
  • Special requirements as per Flag state, local Authorities, Certificate of Fitness, IBC code, Stability and Class
  • Final ullages for all loaded tanks against loading temperature.
  • The order of cargo/ballast tanks to be filled/emptied together with the expected time schedule showing which pumps (if applicable) would be in use.
  • The number of controlled stages required depending on intended cargo operation and ship’s design.
  • The required ballast condition for each stage of the operation.
  • The expected stress, stability and draught conditions at each stage of the operation and damage stability verification as per IBC code
  • The operating envelope of shore loading/discharge arms
  • Coating Compatibility
  • Density, temperature and other relevant properties (Hazard, Flammability & toxicity)
  • Heat adjacent
  • Toxicity of cargo
  • USCG cargo compatibility
  • Quantity and grade of each parcel
  • Transfer rates and maximum allowable pressure
  • Cargo Pollution Category
  • Fire protection including fire fighting
  • Notice of Rate Changes – Venting requirements, over and under pressurisation
  • Vapour emission control requirements
  • Emergency stop procedures
  • Antidotes and Toxic Gas detectors for each cargo as applicable
  • Action to be taken in event of exposure, fire and spill
  • Protective equipment requirement, antidotes and toxic gas detectors
  • Tank environment control as per IBC code (Inerting, Blanketing, Padding requirements)
  • Precaution against Static generation.
  • UKC Limitations
  • Crew familiarity
The Chief Officer, in conjunction with another officer, will ensure that all valves on the cargo and ballast systems, including the pumproom, whether in use or not, are correctly set for the intended operation.

The Cargo Loading/Discharge Plan is to be approved by the Master and signed by each Officer and Pumpman involved in the cargo operations. Junior Officers should, whenever possible, be actively encouraged to assist in cargo planning, line setting and the execution of ballast and cargo activities. This plan is to be discussed and agreed in writing with the terminal personnel as described in these procedures.

The following conventions/rules, procedures and manuals must be complied with when preparing/planning cargo loading operations.
  1. Load Line Convention
  2. IBC Code/BCH Code
  3. Certificate of Fitness
  4. Ship’s stability information
  5. Resistance list for stainless steel
  6. Resistance list for cargo tank coatings where applicable
  7. Cargo hose resistance list
  8. MEPC 2/Circ.
  9. Product information
  10. Chemical Hazard Data Sheets / Material Safety Data Sheets
  11. Tank filling Limits
  12. P&A Manual
  13. U.S. Coastguard Compatibility Chart (See section 16)
  14. USCG CHRIS code (Condensed)
  15. ICS Chemical Tanker Safety Guide
  16. ISGOTT
  17. Local Regulations

Related Info:

Voyage planning and related considerations

Preparation for cargo operation

Preparing a cargo tank atmosphere

Cargo unloading operation safety precautions

Liaison between ship and shore

Cargo line leakage countermeasures

Checklist for handling dangerous liquid chemicals in bulk

Recommended temperature monitoring equipments onboard

Practical example of solving tank cleaning problems

Pre-cleaning /washing of cargo tanks

Risk & hazards of chemical contamination onboard

Cargo compatibility and reactivity of various chemical cargo

Poisoning and required first aid treatment onboard

Chemical tanker safe mooring practice

Determining presence of contaminants in chemical cargo

Handling various grade liquid chemicals during loading

How to prepare a cargo loading or discharge program ?

How to avoid solidification in cargo tanks ?

Cargo segregation requirement for chemical tankers

How to arrange disposal of tank cleaning waste ?

Restrictions on discharge cargo residue into sea

Retention of slops on chemical tankers

Vapour emission control requirement for chemical tankers

Handling self reactive chemicals

Handling of toxic chemical cargoes

Pre-loading meeting safety consideration

How to determine chemical cargo temperatures at different level ?

Cargo line clearance requirement for chemical tankers

Care of cargo pums - risk of pump overload or underload

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