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Since chemical products have high pu‐
rity and corrosiveness, corrosion protection and
prevention is very important. The popular types
of chemical tanker plate material is made from
special types of stainless steel with a high resis‐
tant to corrosion from acid. Stainless steel used
for bulkheads can be solid stainless steel or mild
steel clad with stainless steel. Rubber is some‐
times used to line tanks carrying products
mainly acids, which are unsuitable for use with
stainless steel or coating. Zinc silicate is fre‐
quently used in tanks designed to carry alcohol
as well as some types of solvents and other
chemicals. It is necessary to inspect zinc coated
bulkhead after they have been dried to ensure
the coating has not been softened or otherwise
damaged.
The requirement for coating application
is under MARPOL Annex II (Regulations for the
Control of Pollution by Noxious Liquid Sub‐
stances). Before coating application, the steel
temperature and relative air humidity in the tank
are two basic factors to observe in ensuring the
correct coating application. The application of
coating starts from the bottom of the tank to the
ceiling, because during application the evapo‐
rated solvents may flow to the bottom of the
tank. Hence, the air in the tank is both renewed
and dehumidified to keep clean atmosphere and
steady temperature and humidity conditions.
Figure 2: Application of coating
MIMET Technical Bulletin Volume 1 (2) 2010
The sequence of coating application also plays an
important rule. If we consider a coating system of
two parts (2 coatings), then we should apply the
first coating to all tank surfaces for a specific dry
film thickness. At this stage, as we approach the
ceiling we must cover the tank bottom to avoid any
overspray.
Figure 3: Coating application sequence
Some cargoes are required to be carried at
certain temperatures. For that reason, heating coils
are installed in the cargo tanks to keep the cargo at
the required temperature. The heating substance is
oil or water coming from a heat exchanger, so en‐
able the cargo to be carried at a desired range of
temperatures (ExxonMobil, 2002). Chemical tankers
must have a system for tank heating in order to
maintain the viscosity of certain cargoes. Typically
this system consists of a boiler which pumps pres‐
surized steam through so‐called “heating coils”
made from stainless steel pipes in the cargo tanks,
thus transferring heat into the cargo, which circu‐
lates in the tank by convection.
In SOLAS Chapter II‐2, Regulation 4 Para‐
graph 5.5, tankers are also required to be fitted with
an inert gas system. With the inert gas system, the
protection against a tank explosion is achieved by
keeping the oxygen content low. It will reduce the
hydrocarbon gas concentration of tank atmosphere
to a safe proportion. The problem is that impurities
such as carbon and moisture are normally present
in flue gases and it is difficult to use a conventional
inert gas system with some chemical.
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