Cargo hold Swept cleaning, Washing down, Use of chemicals, Limewashing & Drying holds technics

Fig: Residue of previous ore cargo caught in the frames

Swept clean or shovel clean

The quantity of cargo residues remaining in a hold at the completion of discharge may vary considerably, for a variety of reasons. The master may have control over some of these; for example, after discharging a steel cargo, it may be possible to persuade the stevedores to remove lashing materials, which will greatly assist the crew in their hold cleaning. Often a charterparty will specify that the ship is to be redelivered swept clean or shovel clean. If it is swept clean, the stevedores at the discharge port should sweep the holds before completion of discharge in order to minimise the remaining residues; if it is shovel clean, the stevedores need do no more than discharge cargo that can be easily accessed with a mechanical shovel or a Bobcat.

If a ship is redelivered with holds that are shovel clean, several tonnes of cargo, might remain in each hold. This must all be swept up by the crew and brought on deck for disposal as permitted. Hold cleaning and cargo removal might take weeks, depending on the amount remaining onboard and available resources.

During the sweeping operation, care should be taken to ensure that:

any residues that may be trapped in places such as accessible pipe guards, access ladder trunkings, behind frames and frame knees, are removed
hatch cover undersides, if not boxed in, are swept to remove any residues that have accumulated under the covers
hatch coamings, hatch trackways, hatch access ladders and internal ladder spaces are cleaned
during this sweeping process, the hold bilge wells should be opened and cleaned to remove any residues that may have fallen into them

The parts of the hold that crew can access for cleaning may be limited, particularly in the larger handymax, panamax and capesize ships, because of the dimensions of the holds. Some high-level access may be possible only with scaffold towers, if these can be safely rigged. Even with such equipment, there will still be areas that are inaccessible.

Fig: Applying the prewash

Hold washing down

Once sweeping and removal of the residues has been completed, the next task with most bulk cargoes is to wash down the holds and hatch covers with seawater.

This seawater may be delivered from hoses at the pressure supplied by the deck fire main, or from enhanced delivery systems such as the Stromme Combi-Jet or Maxi-Gun. The Combi-Jet is capable of delivering a water jet over a distance of 30m to 40m, while the Maxi-Gun delivers to a range of 60m to 80m.

When washing down, the crew should take care to ensure that the upper reaches of the holds are washed thoroughly to dislodge any residues that may be trapped in the upper structure, behind pipe guards, on cross deck structures, etc. This is particularly important in parts of the hold that are physically inaccessible. During the wash-down, loose paint or rust scale will be dislodged, particularly where the water is delivered by an enhanced delivery system such as a Combi-Jet or Maxi-Gun

Depending on the nature of the previous cargo, this wash-down may be sufficient. With certain cargoes, residues or staining may remain even after a thorough wash-down. To remove these, it is necessary to use targeted chemicals.

For cargoes such as coal and petcoke, which leave staining, it is often necessary to use heavy-duty alkaline detergents, which are applied as an emulsion, need time to take effect and are rinsed away with seawater. More than one application will be needed to remove stubborn stains. If using chemicals for cleaning, reference should be made to the safety data sheet concerning safety precautions and handling.

A common test in countries including the USA and Australia is for the surveyor, wearing light-coloured gloves, to run his hand across the hold bulkheads. If there is any discolouration of the gloves, the hold fails the cleanliness survey.

For cargoes such as cement and cement clinker, which often leave a sheen of residue on surfaces such as the sloping plates of the upper hopper tanks, it is necessary to use diluted acids to remove those residues. The most common acid is hydrochloric acid, which is also known as muriatic acid. The diluted acid is applied directly to the residue, given time to take effect and then rinsed away. Where residues are tenacious, many applications of acid may be required or the residue may have to be physically scraped away.

When scale and rust has been removed by a high-pressure water wash, it is prudent to check the holds a few days later, since water caught behind paint and scale can later dislodge rust scale. The holds in any event should always be checked again before arrival at the load port to ensure that no previous cargo residue has been dislodged by the ships movements and vibrations.

Steel-plate manhole covers should be removed to allow access to the lid recess below, and container fittings on the tank tops, ladder recesses and platforms must be thoroughly cleaned.

Fig: Using the chemical cleaning lance

Use of chemicals

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

Prewash 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.

Cleaning chemicals

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.

Limewashing

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
limewashing
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.

Freshwater rinse

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:

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.

Washings containing hold cleaning chemicals

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.

Drying holds

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.

Related information

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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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