Vol.2 January 2003

P&I Loss Prevention Bulletin
Japan Ship Owners Mutual Protection & Indemnity Association
Claims Administration Divsion, Claims Department

Prevention of accident damage to cargo loaded on Bulk Carriers
Case 2 ) H eat Damage c a use d by he a t t ra nsf e r f r o m
th e Fuel O i l Ta nk s

I n Case 1 we explained about seawater damage, and now we discuss heatdamage caused by heat transfer from bunker tanks. This occurs quite frequently.
These days, vessels use high viscosity low quality heavy fuel oil which isunpumpable at low temperatures.
So heating of the oil in these tanks isnecessar y to enable it to be pumped from the double bottom or deep tanks to thesettling tank in the engine room.
Due to the increasing use of high viscosity low quality oil, cargo damage causedby the heating of fuel oil beneath the cargo holds happens more frequently.

1

Grain in Bulk is easily affected by heat

Most easily damaged by heat transfer from fuel oil tanks are Soybeans and Maize but
Wheat, Rapeseed, and other bulk grains are also occasionally heat damaged as isSoybean Meal.
Soybeans are especially sensitive to heat, and if the temperature of the beans reaches
a b o u t 4 0 oC t h e b e a n s w i l l b e c o m e w i t h e r e d a n d l o s e t h e i r a b i l i t y t o s p r o u t , a n doxidisation is increased.

22. Fuel oil tanks

Generally, fuel oil tanks causing heat damage are as follows :・ Fuel Oil Tanks in double bottoms
・ Deep Tanks located forward of No.1 hold・ Fuel Oil Settling and Service Tanks located at the fore end of engine rooms

Cargo loaded in the aftermost hold is occasionally damaged by heat transfer from theengine room.

3

Type and pattern of damage to cargo caused byheat transfer from each tank・ Double Bottom Fuel Oil Tanks
The number of tanks varies depending on the type of vessel, but generally, vessels ofPanamax type have seven holds, and the fuel oil tanks are located only underneathNos. 5, 6 and 7 holds.

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3Sequel・・・・

When the fuel oil in those tanks is over heated, the plating above the tanks may
become warm, and as a result, the cargo may become discoloured, caked and mouldy,and sometimes the cargo may be carbonised. Although the type and the extent of thedamage will vary in proportion to the moisture content of the cargo and the degree ofheating of the fuel oil, typically the cargo may be damaged up to a height of some 2 to
3 meters above the tanktop, and the temperature of the beans may rise to some 80 o C.
Moreover, in rare cases, the whole cargo in a hold may have to be treated as damaged.
From experience, the degree of damage to cargo in No.7 hold is often worse than in
No. 5 and 6 holds, and this is usually due to the fuel oil heating lines for the oil in thetanks under the No. 5 and 6 holds or in the deep tank located at forward of No.1 hold,passing through the tank under No.7 hold, and so, the duration of heating of the tankunder No. 7 hold is longer than for the other tanks.

(Damaged conditions and pattern

are shown in the photos below)

Showing beans heated to 87.0 o CShowing heavily caked and discoloured
cargo of 1m thickShowing gathering of the damaged cargo

Heavily discolored and caked cargo

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3Sequel・・・・

・ Deep Tank located in front of No.1 Hold
Not all vessels are equipped with a Deep Tank, but some have a Deep Tank between theChain Locker and No.1 hold. When the fuel oil in this tank is overheated, the cargo in
the fore part of No.1 hold adjacent to the aft bulkhead of the deep tank may bedamaged similarly to the cargo on the double bottom tanks, described previously.

Thedamage may extend some 1 to 2 meters from the forward bulkhead of No.1 hold, andmay reach the level of the tanktop. (same depth as the deep tank)(Damaged conditions and pattern are shown in the photos below)

Damaged cargo along the fore bulkhead in No.1 hold cargo

Showing heavily caked and discoloured

・ Fuel Oil Settling and Service Tanks located at the fore end of the engine room
A few vessels have the Fuel Oil Settling and Service Tanks along the sides in the middle ofthe engine room or at the aft end, but in most vessels, they are located some 30cm awayfrom the forward bulkhead near the vessel’s centerline.

These tanks are joined to theforward bulkhead by the bottom plates of the tanks and by brackets, etc., at the top of thetanks. Therefore, if the fuel oil in these tanks is heated too much (Generally, it is heated
to 80 o C for the settling tank, and 90 o C for the Service tank), the cargo along the aftbulkhead in the hold adjacent to these tanks may sustain heat damage in the same manneras the cargo along the forward bulkhead of No. 1 hold.

Showing heavily caked and discoloured cargo along
bulkhead plates between the engine room and theaftermost holdー7ーMouldy cargo in the top surface along
the aft bulkhead of the aftermost holdP&I Loss Prevention Bulletin
4Damage prevention planO f course, in order to prevent heat damage to the cargo by heat transfer from the tanks, thefuel oil in the tanks should not be over heated or heated longer than necessary.
In addition, the following precautions should be taken.

a Most of the serious heat damage occurs because the Engine Department often do not fully understandthe character of the cargo, and so the fuel oil in each tank is heated too much. So, when a cargo of Bulk
Grain is loaded, it is important to have good communications between the Engine and DeckDepartments.

b Usually, the heating lines in the double bottom tanks are installed at a height of about 10cm from thetank bottom. From past experience, when the heating lines are exposed above the surface of the oil orare at the same level, the amount of heat transferred to the tanktop plates is greater than when thetanks are full or have a lot of oil in them.
Therefore, sufficient oil should be left in each tank when shifting consumption to the next tank. In thisconnection, it is also important to take into consideration the order of consumption. Experience showsthat heat damage has frequently occurred to the cargo in the after hold, because of oil consumption
starting from the after tank to the fore. It is recommended that the order of consumption of the oilshould be from the bow to the stern.

c Heavy fuel oil of 180 or 380 centi-stokes (unit of kinematic viscosity) is now generally used. Although
there will be a cost factor, in order to prevent damage to Grain Cargo, the use of heavy fuel oil having aviscosity of 180 centi-stokes is recommendable as this can easily be transferred without heating to hightemperature.

d To heat the oil in the double bottoms or deep tanks, the steam valves are only cracked open (1/16 to 1/4rotation), and the valves are operated manually. Since the vibration of the vessel may cause the valvesto open further, a stopper should be applied to prevent this happening. Sometimes, it is thought that
fuel oil heating steam lines are completely closed, but actually they are not due to incorrect operationor a defect in the valve so steam continues to flow through the heating lines. This is a common cause ofheat damage.
The valves must be correctly operated, frequently checked and properly maintained.

e During the voyage, the steam generated by the exhaust gas economiser may exceed the amount requiredby the vessel and sometimes the surplus steam is circulated in the fuel oil tanks' heating lines todispose of it. When this is done, the fuel oil in each tank will be continuously heated, and serious heatdamage will occur.
Therefore, when surplus steam is produced, other methods of dealing with it should be used.
- End<With collaboration from Nippon Kaiji Kentei Kyokai（ NKKK）>
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