Maintenance and Inspection of Cargo and Ballast Tanks and Other Compartments

7. Maintenance and Inspection of Cargo and Ballast Tanks and Other Compartments

7.1 Implementation of an Inspection Routine

Every cargo and ballast tank, and other compartments such as holds, cofferdams, void spaces, ducts and water tanks should be inspected at least annually.

The exception to this requirement is the cargo tanks of crude oil carriers, or product carriers continuously carrying heavy oil, where the tanks are not regularly cleaned. The cargo tanks on such vessels must be inspected as and when it is possible to do so, such as when a tank has to be cleaned for repair work. However, if a period of 30 months is approaching since the last cargo tank inspection then the operator should be consulted well before the 30 month anniversary to try to arrange a suitable opportunity to clean and inspect the cargo tanks.

It is important that an accurate record is maintained for each compartment. On larger vessels the inspection of compartments such as ballast tanks can be a very complicated process and in order to ensure that adequate records are maintained it may prove necessary to divide the compartment into transverse sections and use more than one form for each compartment.

Every effort must be made to accurately record coating breakdown and corrosion. If records are accurate then any deterioration in the condition of the compartment can be monitored.

The Records – Tank Inspection (ECF15 - Fore Peak, ECF16 - Aft Peak, ECF17 - Double Bottom, ECF18 - Side Wing Ballast, ECF19 - Generic,) should be used to maintain a record of the compartments inspected, and they should be forwarded to the Technical Department once completed.

All reports should be filed and retained on board as well as forwarded to the Technical Department.

Double hulled vessels present specific problems with respect to the inspection and maintenance of those spaces. The reasons are as follows:

• The relatively numerous and confined compartments of a double skin design make the surface preparation and paint application at the building stage more difficult, thereby increasing the likelihood of coating breakdown;

• A relatively larger area of ballast tank boundaries adjacent to cargo or bunker tank boundaries presents a greater risk of leakage from one to the other;

• The greater amount of ballast tank area adjacent to cargo tank boundaries, particularly during the carriage of heated cargoes, will lead to the formation of more condensation within the double skin, with consequential corrosion potential;

• Interaction between the inner and outer hulls, caused by loading stresses and differential expansion, increases the possibility of fatigue cracking;

• The number of relatively small compartments with reduced ventilation capability can result in pockets of hydrocarbon vapours occurring;

• The reduced and often difficult access to all double skin compartments makes the monitoring of coating condition and the rectification of defects more difficult.

7.2 What to Check for During Inspections

The following is very broad guidance and reports on the inspection of a compartment should contain as much descriptive detail as possible in order for the condition to be adequately assessed by the office.

7.2.1 Coating

The condition of the compartment coating should be carefully checked. The coating is the key to preventing corrosion. Guidance in inspecting coatings is as follows:

• Breakdown of the coating is likely to occur first in areas of insufficient film thickness, such as on the leading edges of frames and lightening holes;

• Areas of the tanks where air may be trapped when the tank is ballasted, as well as areas from which it is not possible to remove all the water, when the compartment is empty, are important points to check for the onset of coating breakdown and corrosion;

• Any cracks found in the coating may indicate stress points in the vessel's structure and must be carefully checked;

• The coating in areas beneath suction bell mouths should be given special attention. High coating abrasion in these areas may quickly lead to breakdown and the formation of pitting;

• Attention should be paid to the coloration of the coating. Changes in shade may indicate corrosion beneath the paint.

The condition of the coating should be reported as accurately as possible. It is often very difficult to describe the level of breakdown and simple comments such as “10% breakdown” are unhelpful and non-descriptive. Records should give the exact location of the breakdown, and should state whether it is coating breakdown, if corrosion is evident and the type of corrosion, whether surface powder rust, or penetrating rust. If there is hard rust evident then this should be recorded.

Where there is damage to a coating the steel should be prepared and recoated at the earliest opportunity.

7.2.2 Structure

The Master or Chief Officer should, when circumstances permit, take the opportunity to visually check the external hull whilst alongside a berth. If indentations or other damage more than very minor are observed, the extent and location of the damage must be reported to the office, and a record made on board. Photographic evidence must only be taken in accordance with company safety procedures.

During the inspection of a compartment, checks should be made for cracks, deformation, and corrosion. Guidance in inspecting for structural damage is as follows:

• Cracks are most likely to occur where frames, girders, and webs are attached to the double hull and where there are structural discontinuities. The first indications of cracking are likely to be damage to the coating;

• It should be remembered that once a crack has formed, it will propagate and may well penetrate either the outer or inner hull. Therefore, if a crack is detected, its full extent should be determined and then should be monitored until a repair can be affected;

• Deformation, such as the buckling of frames, webs and plating, is a potentially serious problem and any indication should be very carefully checked. It is likely that severe stress has been placed on those structural members. Reasons can be poor design, heavy weather, impact damage, or under or over pressurisation during cargo operations.

Any structural issues must be immediately reported to the company.

7.2.3 Corrosion

Corrosion must be kept under control. The maintenance of coatings is vital in the prevention of corrosion. Where break down of coatings is noted then remedial action must be taken as soon as possible.

It should be remembered that the problem of condensation and corrosion is accelerated when heated cargoes are carried or in spaces subject to condensation, and if necessary a more frequent inspection regime should be followed.

Areas where corrosion is often difficult to control are sounding pipes, striking plates, hangers, brackets, and pipe work generally.

Particular attention should be paid to the plating under suction bell mouths, where pitting may occur. These areas are difficult to check because bell mouths are placed close to the plating, but nevertheless it is very important that they are examined carefully.

7.2.4 Coating Maintenance

Through regular inspection the condition of the coating, which directly affects the condition of the steel, is monitored and plans can be made for repairs to be carried out while the damage is still relatively minor.

However, in some areas of double skin spaces this may not be practicable and surface preparation has to be carried out using hand tools. A surface tolerant coating should be used to ensure that the repair is effective.

The manufacturer's instructions should be followed regarding the preparation quality and method of application of the paint.

Repairs to steel structure, should defects be found, should not be attempted by the ship's crew.

Full details of the defect should be reported to the company in order for a repair schedule to be drawn up.

7.2.5 Sediment

Occasionally a vessel will be required to ballast in places such as rivers where there are significant amounts of sediment suspended in the water. If sediment is found during a ballast tank inspection then the amount should be estimated and recorded.

In accordance with the requirements of the Ballast Water Management Plan, the sediment should be removed at the earliest opportunity.

7.2.6 Anodes

Where anodes are fitted the condition of the anodes should be reported, in terms of the percentage of wastage. Where the wastage is greater than 75%, the anodes will require scheduling for replacement at the next docking.

7.2.7 Bilge Pumping and Sounding Arrangements

The condition of the bilge pumping arrangements in non-cargo or ballast tanks should be checked, particularly pipework.

7.2.8 Enclosed Space Entry

The requirements of the company enclosed space entry procedures must be strictly complied with when carrying out compartment inspections.