Clinker is the main ingredient in cement production. Clinker loading and hold cleaning is similar to cement, except that clinker does not contain a binding agent and thus does not harden to the same degree that cement does.
Cement clinker is the semi-manufactured material which needs to be ground into powder to make ordinary cement. It may present fewer problems than the carriage of cement. Its biggest advantage is that it does not harden when in contact with water, reducing the damage it can cause to the vessel. It must, however, still be kept dry so as to prevent it from caking. Contamination with seawater also results in an increase in its chloride content, adversely affecting the cement produced from it.
Fig: Loading cement using a closed loading system
Cement may have a temperature of 110ºC when leaving the production site and can sometimes be loaded at up to 80ºC. Temperatures as high as 100ºC have been recorded and this can lead to problems with the hold coatings, and potential dangers with the fuel oil double-bottom tanks.
Cement is often exported from regions with low sea temperatures and discharged in warmer areas with high air humidity. After being loaded, the powder volume of cement can contract by as much as 10% once it has settled. In these conditions, water vapour can condense, and solidify the cement, particularly on the surface, not only under the main deck areas but in other parts of the cargo holds.
Often when loading cement, a ship will be fully ballasted when first alongside, and the top side ballast tanks are dropped as loading progresses. This can produce sweating on the top hopper side plating, which allows the cement dust to adhere, and become difficult to remove.
The point at which water vapour condenses in the atmosphere is called the dew point. When the incoming air or the steel has a lower temperature than the cargo in the holds, this allows the surrounding air to cool and produce vapour which condenses. As the wet cement dust dries on the hold frames, it hardens and poses a major cleaning problem. This is often only overcome with determined manpower, efficient wash-down equipment and chemicals. Ballasting of cold water adjacent to (warm) cargo holds can have the same result. The problem can be reduced in some cases by good ventilation, weather permitting.
Cement cargo in bulk can:
Cement cargo hold preparation and cleaning before loading:
- solidify when wet
- retain heat for a considerable period when loaded warm
- easily stick to non-smooth surfaces
- be affected or contaminated by residues of previous cargoes. These may reduce the cements binding capacity
- produce considerable dust causing problems in the upper parts of the holds
- the holds (sides and tank top) and bilges must be completely dry
- cargo holds should be clean and odour-free. Residues from previous cargoes such as sugar and fertilisers may cause problems and result in a failed hold inspection. A small amount of sugar can seriously degrade a cement cargo ensure that the hold is completely free of previous sugar cargo residue
- the hold air should be dry ahead of loading; use dehumidifiers if on board for several days before loading
- condensation during the voyage should be avoided
- cold water ballast should be avoided if possible in tanks adjacent to holds being loaded
- all holes and indents on the tank top and bulkheads and all scupper holes should be dry and clean. Consider covering manholes and recesses with plastic sheets and masking tape
- if the climate is warm and humid, the hatches should be closed once discharging has been completed, so that a dry atmosphere can be maintained inside the holds
- the bilge, bilge wells and tank tops should be cleaned thoroughly and dried before loading. Cement getting into damp bilges and bilge wells can build up trouble. Clogged bilge lines with hardened cement can be a major problem
- bilge well strainers and bilge well lids must have clear drain holes, and be clean and free of debris
- non-return valves in the drain and bilge system must be checked and confirmed as operational. Claims have arisen where the non-return valves have allowed water to flow into the holds via the bilge line system. When this occurs with a cement cargo, the result can be extremely expensive and time-consuming. It could be necessary in such cases for the bilge lines to be replaced
- the bilge wells must be protected using good-quality hessian that is firmly in place so as to allow water to be drained in an emergency
- good cleaning equipment must be available
- chemicals to dissolve hardened cement may be required
- crew should be equipped with personal protective equipment Remember: after carrying a sugar cargo, the hold must be cleaned to a very high standard. Sugar residue will contaminate a cement cargo. Paint protection
- Use of paint protective chemicals such as prewash products can assist the cleaning after discharge
General precautions against dust:
Fig: Loading cement caused a lot of dust
The loading process into holds results in the creation of large amounts of cement dust settling on all exposed areas. All areas must be swept and/ or washed down after the completion of loading to prevent loose cement from hardening if exposed to seawater or rainwater during the vessels journey .
- all accommodation, mast houses/store rooms and vents should be shut
- wire drums and electrical boxes on deck should be covered and closed off
- pilot ladders should be covered
- air conditioning should be on recirculation
- deck scuppers should be blocked
After loading before departure:
- the atmosphere in the cargo holds should be kept as dry as possible; hatch cover lids should be closed when the holds are not being loaded or discharged particularly if there is a possibility of rain
- the main deck, hatch covers and any exposed piping should be cleaned with compressed air, this may be forbidden in certain ports by anti-pollution regulations
- if possible, main deck, hatch coamings and covers should be swept and cleaned by compressed air, and given a good sweep before washing down
- hatch coaming trackways, drainage channels and drain holes should be cleaned and free of cement if possible weather permitting. Blocked drain holes and channel bars will become clogged with hard cement in heavy weather or rain
- cement dust should be dry-cleaned using brushes, removing the majority of cargo residues from the tank top and bulkheads
- crew or stevedores should follow up in the cargo holds when the discharge is almost completed. Cargo residues should be collected and filled into the grabs for landing. Shovel clean means that the stevedores discharge only what they are able to get into the grabs without sweeping
- bilge wells should be dry and free of cement dust
- cargo hold bulkheads, hatch cover undersides and hatch comings should be cleaned by compressed air and covers should be swept
- remove all solid residues, sweep clean and flush with seawater, using high-pressure hoses. After dry-cleaning, the holds must be cleaned by high-pressure air/water. Chemicals and high-pressure cleaning pumps can be used when necessary
if hard residues are not removed by conventional high-pressure hoses using seawater, it may be necessary to call in a professional cleaning company, which can use acids to remove the persistent hardened cement. Hard cement residues, if not removed during the high-pressure wash, can be removed by high-pressure cleaning machines or acid cleaners.
Hydrochloric (muriatic) acids must be handled with care and advice should be sought from the hold paint manufacturers. The acids are harmful to the human body, and may eat into hold paint. The recommended dilution with freshwater is 1:5. Stronger dilutions may be necessary, but this may result in pitting the hold steel. Again, always check with manufacturers recommendations
The chemical mix should be applied using only a stainless steel lance kit connected to a pressurised mixing tank or an air-driven pump, either made from stainless steel or polypropylene, both with wetted parts made of Teflon. The chemical mix must be removed before it dries, working from the bottom up. This is most easily done from tank top level with Maxi-Gun or Combi-Jet. The cleaning operation is always completed by flushing with freshwater to remove salt residues, working from the top down.
The volume of chemicals used must be monitored and guidance sought from the manufacturers. Chemical splash suits, chemical gloves, boots, helmets with visor and breathing mask must be worn. Material Safety Data Sheets should always be consulted.
- all areas should be flushed with freshwater
- to avoid blocking the bilge system, portable diaphragm pumps may be used to remove the washings
- the bilges and tank tops should be cleaned thoroughly before washing the holds. The bilges should be flushed for a minimum of 30 minutes before drying the tank top to ensure that they are not clogged by cement. Clogged bilge lines with hardened cement can be a major problem
- all valves in the drain/bilge system must be checked
Only the most powerful cleaning equipment will remove hard layers of cement. Normal ships cleaning equipment might look adequate but often fails, particularly in terms of completing the work in a timely manner. Practical experience with chemicals has been mixed and there is a danger that they can adversely affect paint systems and ancillary equipment such as bilge pumps.
Recently, some ships have begun the practice of applying special barrier chemicals in the holds before loading. These protect the steel and paint from the cargo and make the cleaning process easier. They need to be applied in a controlled way and always according to the manufacturers recommendations. Some chemicals are reported to be difficult to remove and may cause problems when cargo holds are repainted.
Read more on Bulk cement loading, discharging, problems with dust and temperature monitoring guideline
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