The removal of corrosion spots on different ship surfaces on the early period allows stopping the spread of corrosion spots in the future.
Here is a simple calculations on the example of newbuilding chemical tanker DWT-52 thousand tons of ballast tanks surfaces, where the ballast tanks area is about 120 000 sq.m.
In this case each company manufacturing pain materials under coordination of the warranty period (taken 5 years as the basis ) stipulates annually % of surface damage.
We are surely to use the averaged values which will be:
The Table of damage tolerance by years
|rate of frequency By years||the percentage of corrosion damage,%||corrodible surface, sq.m|
|Total in 5 years||5%||5880 sq.m.|
This warranty period has expired, and the corrosion process is developing. The ballast tanks repair usually falls on the 9th year the ship operation during the ship repair, thus it is possible to predict the future situation of corrosion progressing in ballast tanks
|Period by years||Percentage of corrosion ,%||
Surface damaged by
progress of corrosion on
the surface in 9 years
Therefore the ballast tanks shall have 21,000 square meters of corrosion damage on the 9th year during ship repair in dry dock.
The repair of damaged surface during the sailing and berthing with the least costs is suitable to be done in the wing ballast tanks, which make up about 50% of the total surface or 10,560 square meters.
The cost of paint coating repair in the wing ballast tanks during sailing after the expiration of warranty shall be:
|Period by years||Duration of Repair in months||Number of Ship painters||Cost per 1 Painter, in USD||Sum In 6 months in USD|
The repair of 10560 sq.m. shall make up 108 000,00 dollars or the cols of 1 sq.m shall be 10,28 dollars, which makes at least 20-25 % under cost of work performance at the ship-repairing yards of Europe, and the most important thing is the reduction of ship repair for 15-20 days.
The result is obvious.