Trans RINA, Vol 153, Part A4, Intl J Maritime Eng, Oct-Dec 2011 3.2 PAINTING OF PMA
In order to obtain a long service life, the coating on the PMA should be applied to the same standards as for the ballast tanks themselves. Photograph 1 shows a well prepared ballast tank.
Photograph 2. Corroding zinc on the PMA itself is removing the paint.
Photograph 1. Ballast tank with well prepared PMA. 4.
SERVICE PERFORMANCE 4.1 BALLAST TANKS
The presence of the stiffening in ballast tanks allows the cargo holds and tanks to consist of mainly smooth, flat surfaces. This aids the removal of cargoes and cleaning of the holds.
The addition of PMA into ballast tanks, for example in the double side skin of tankers, creates many more edges and welds to protect and many more potential sites for mechanical construction.
damage and touch up work during
If the PMA is not well maintained, premature paint failure and corrosion can cause corrosion that may well propagate to the adjacent structure. As stated above, the PMA is
premature coatings failures may interrupt
part of the statutory requirements and any the ship’s
operation by the port authorities and be off hire at a cost to the owners and operators.
Many of the PMA are constructed from galvanised steel to provide an enhanced life to the structure. However, the galvanised surfaces must be carefully prepared and painted, otherwise the zinc on the PMA can act as part of the ballast tanks cathodic protection system, as shown in photograph 2.
In these cases, the galvanised layer dissolves sacrificially to protect the steel. This forces the coating off the PMA and allows premature corrosion of these structures. The inclusion of additional sacrificial anodes may be required specifically to protect the PMA.
Photograph 3. Corroded PMA.
For ships with cargoes that have the possibility of high microbe content, such as sour oils, the presence of PMA may increase the risk of providing suitable environments
©2011: The Royal Institution of Naval Architects A-245
Maintenance and repair of the coatings on PMA will become increasingly difficult with time in service due to the problems of successfully painting corroding zinc layers. This is in addition to the many other difficulties encountered in painting complex structures under service conditions. Such problems include cleaning, surface preparation, paint application, and paint curing.
All of
these are difficult to achieve well whilst at sea. 4.2 CARGO TANKS
PMA in the cargo tanks, in product carriers, chemical and oil tankers will also experience similar problems to those on bulk carriers.
Cleaning patterns and washing of the additional structure in the tanks will need to be checked to ensure that residue of cargoes are not
trapped and acting as sources of contamination or corrosion.
Good maintenance and repair of the paint is essential to prevent metal loss due to corrosion, as shown in photograph 3.
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