Any discolouration of the hold coating can easily become permanent if not properly cleaned after each, or every second, cargo. The use of chemicals is becoming more common. Studies have indicated success in protecting the paintwork (and thereby allowing easier cleaning of cargo residue), breaking down the cargo residue, or cleaning and degreasing after cargoes such as petcoke or coal, ahead of a full seawater wash down. The chemicals should be washed off before they can dry.
Fig: Applying cleaning chemicals
The use of a prewash can protect the paint coating of the holds and allow for a much easier cleaning after cargoes which are liable to stain. The prewash coating is applied in the same way as the cleaning chemicals (see below) and dries off as a clear protective film. This is then washed off after discharge. Such prewash chemicals are also known as fat cargo slip.
The prewash prevents the cargo adhering to the hold surfaces. Prewash is less effective on rough, uncoated surfaces such as the hold tank top. Application in a handymax ship takes about three hours per hold. Prewash protects the paintwork and can reduce time required for painting in preparation for the next cargo.
There are a number of products available and the manufacturers instructions for mixing proportions and the safety precautions should always be followed. If the recommendation is to use only freshwater to apply the chemical, this should be followed, otherwise the application may be ineffective. Equally, without use of the proper equipment, the application may not work.
The chemicals are usually applied using special equipment including:
- chemical tank
- mini-jet with air pressure of about 7 bar
- lance with foam nozzles and extensions
- personal protective equipment (PPE)
After leaving the applied chemical on the bulkhead for a prescribed time, the chemicals are washed off using a full seawater wash. The operation should always be finished with a freshwater wash. Always check the manufacturers guidance on compatibility with paint systems. Always check with the charterer and/or shippers regarding compatibility with the next cargo.
Hold structures must be protected against aggressively corrosive cargoes, for example salt and sulphur. Limewashing is used as a protective coating before loading such cargoes. Limewashing is a physical barrier application so the thicker it is, the better the protection, but the more difficult it is to remove. Effective barriers against corrosive cargoes are:
- paintwork in good condition
- hold block
The more intact the paintwork, the less limewash or hold block is required. A typical voyage instruction for loading sulphur, for example, will be: The ship to be presented for loading with holds clean/swept/dry/ limewashed and free from residues of previous cargoes, suitable in all respects to receive bulk sulphur to the satisfaction of shippers and charterers. Hatch covers to be in a satisfactory condition to ensure watertightness.
Lime (or calcium hydroxide) is manufactured from crushed and powdered limestone. The problem with limewash is that it is difficult to remove, posing a similar problem to a light cement residue. An alternative is hold block, which is a transparent and environmentally friendly product.
Lime mixture: prepare 200 litre empty drums with about 50/75kg of lime plus 2.5kg of sugar. Fill the drum with hot or warm freshwater and mix thoroughly. A handymax bulk carrier will use about 1,200kg to 1,500kg of lime. For a ship without paintwork intact, 600kg of lime can be used in a 10,000 cubic metre hold. The mixing quantities will vary according to the condition of the paintwork and other factors. The master should always ensure that he has sufficient lime onboard.
Lime application: The mixture is to be applied with a roller or a spray to a height as calculated by the stowage factor. A thicker coat is then applied to those parts of the hold lacking good paint covering, such as the tank top. Special attention paid to areas behind frames and to inaccessible places. No bare metal should be visible. Sometimes a second coat may be applied if, during drying, rusting is visible through the limewash, as this may stain certain cargoes. Lime coating removal: Use high-pressure water washing and possibly caustic or citric acid cleaning chemicals.
Hold block: The supplier should be consulted for the application rates, which depend on the hold condition. The hold block is easily removed using the manufacturers hold wash.
Once the wash-down is judged successful and all residues have been removed, the holds and hatch covers should be rinsed with freshwater to remove any dried salts that have become deposited in the hold structure as the seawater previously used has dried. The degree of a freshwater rinse or wash depends on the nature of the next cargo to be loaded.
Some shippers. surveyors, or terminals, for example, when loading fluorspar, will carry out a silver nitrate test to ensure that the hold is free of all salt deposits.
If the following cargo is to be steel, it is important to remove all chlorides in the hold as any sweating may produce saltwater, which could affect the steel.
Disposal of bulk cargo wash down residues
Care should be taken when disposing of both cargo residues and wash down water to ensure that the requirements of MARPOL 73/78 Annex V are strictly followed.
MARPOL 73/78 Annex V requires that all ships of 400gt and above have an approved Garbage Management Plan and a Garbage Record Book. An amendment that came into force in August 2005 stipulates that cargo residues are treated as garbage. Cargo residues that remain onboard after discharge are thus included in the definition of garbage, and need to be disposed of outside Special Areas (as set out in MARPOL 73/78), and as far away from the nearest land as mandated by the MARPOL regulations. (if it floats outside of 25 miles; if it sinks outside of 12 miles).
The Garbage Management Plan should include minimisation of cargo residue wash-down water and its discharge. Any cargo residues and wash-down water disposals or discharges should be recorded as Garbage Category 4 in the Garbage Record Book, and the entries should include start and stop positions.
MARPOL 73/78 permits exemptions from these regulations where safety may be compromised. MARPOL ANNEX I Regulations for the Prevention of Pollution by Oil. Annex V Reg. 1(1) of the Marpol Convention confirms that if a substance is defined or listed in other Annexes then Annex V does not apply. For a cargo such as petcoke which has a high hydrocarbon content (you can see the oil sheen when washing down this cargo), the hold washings would fall under the requirements of Annex I and can only be discharged in compliance with it.
Annex I Reg 1(1) defines oil as petroleum in any form including crude oil, fuel oil, sludge, oil refuse and refined products
Annex I Reg. 1(2) refers to oily mixture as a mixture with any oil content. Annex I Reg. 2(1) states Unless expressly provided otherwise, the provisions of this annex shall apply to all ships. Therefore Annex I applies to all ships and hold washings containing petroleum products should be disposed of accordingly. Unfortunately, the Annex is not completely clear and was not written with petcoke or other hold washings in mind. Annex I Reg. 9(1) Control of Discharge of Oil sets out that any discharge into the sea of oil or oily mixtures from ships to which this Annex applies shall be prohibited except when the following conditions for dry cargo ships are satisfied; From a ship of 400 tons gross tonnage and above other than an oil tanker and from machinery space bilges excluding cargo pump-room bilges of an oil tanker unless mixed with cargo residue:
Washings containing hold cleaning chemicals
- the ship is not within a special area (see Annex I Reg. 10)
- the ship is proceeding en route
- the oil content of the effluent without dilution does not exceed 15ppm; and
- the ship has in operation equipment as required by Reg 16 of this Annex. This refers to 15ppm oily water filtering equipment which is not fitted to dry cargo ships for use with cargo washings Because of the large quantities of water used in hold washing and relatively low amounts of petroleum content the washings are unlikely to exceed 15ppm; but it would be prudent to take a sample of effluent and ensure that the content is less than the 15ppm, and then dispose of the washings in compliance with MARPOL outside of 25 miles and not within a Special Area.
Such chemicals could in themselves be pollutants. If a substance falls within Annex 1 (Oil) or Annex II (Noxious Liquid Substance), then the washings will have to be disposed of according to the Annex requirements. Check with the suppliers if in doubt.
Cleaning holds within, or close to, port limits may also require local regulations to be followed with respect to the disposal of hold washings. Always check with local agents. It may be necessary to retain the washings onboard or dispose of them ashore using road tankers or to approved facilities. Only approved companies should be used for the disposal of hold washings, and the correct paper work and receipts should always be retained for a minimum of two years.
When the wash-down is completed, the crew should mop up any pools of water that may have collected in tank top indentations and other areas. If the ship is fitted with mechanical ventilation, this should be run to aid the drying process for the rest of the hold. Bilge wells must be dry before being shown to a surveyor.
Almost inevitably, some ship sweat will form on the internal structure of the hold in the interval between completion of cleaning and the hold inspection. Ship sweat should not in itself be a reason for holds to fail an inspection. The inspector may require any excessive quantities to be wiped dry during the inspection, but having satisfied himself that the source of the moisture is ship sweat and not water ingress, the surveyor should accept the hold as clean.
Cargo hold cleaning problem and related guideline
Cargo hold maintenance guideline
Hold preparation checklist -Cleanliness/preparation, additional measures
Cargo holds readinesss, maintenance requirement, preventing stevedore damages & safety aspects
Cargo hold inspection -Reasons for failing hold inspections
Chief officers final inspection prior cargo hold survey
Maintenance procedure for mechanical steel hatch covers
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- Hold cleaning in bulk carriers- Preparation for grain loading
- Chief officers final inspection prior cargo hold survey
Operation of sea going bulk carriers involved numerous hazards . Careful planning and exercising due caution for all critical shipboard matters are important . This site is a quick reference to international shipping community with guidance and information on the loading and discharging of modern bulk carriers so as to remain within the limitations as specified by the classification society.
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