Trans RINA, Vol 153, Part A4, Intl J Maritime Eng, Oct-Dec 2011
structural members, coatings and the ballast line itself. In the double bottom ballast tanks the access spaces between the ballast line (if fitted) and the inner and outer bottom longitudinal may not be sufficient
in size
(minimum width of 600mm) to achieve safe access over and/or under the ballast lines.
Thus, additional 800mm x 600mm manholes may be required to be provided in the floors and/or double bottom girders to ensure that a stretcher and/or a person, (allowing for an oversize person too), wearing a self- contained air-breathing apparatus can escape from the space under consideration. This may produce significant alteration to the design of the floors and/or girders, as such holes diminish the strength of the respective members in both shear and buckling failure modes.
A similar design problem occurs at the lower end of the side transverse web in way of the double side skin area just above the upper end of the lower hopper. This is a classic problem that several designers addressed from the structural point of view, but not from the corrosion aspect. Work in 2003 [5] showed that it is more difficult for hard coatings to resist high shear and buckling as well as high strain and in these areas (as shown in figure 1), such forces are predominant.
The reason is
PSPC, required by SOLAS II-1 Part A Reg. 3-2 PSPC are not tested for mandatory. In this
that hard epoxy coating formulations, flexibility as these tests are not
regard the designer may have to
consider the provision of T-Ring stiffeners around the opening to ensure that the required coatings target life expectancy of 15 years in these critical areas will be achieved.
assessment criteria as indicated in Table 1 of MSC.1/Circ 1330. However, in cargo tanks and ballast tanks within the cargo area of a tanker outside 0.4L (i.e. in way of the foremost and aftermost cargo tanks) this has not yet been established in the IASC Common Structural Rules (CSR) for oil tankers.
The CSR methodology for the 3D 3-tanks length of FEA is still outstanding, although the CSR for oil tankers have been in force since 2006. ABS have published a guidance notes for the “Strength Assessment of the Cargo Tank Structures Beyond the 0.4L Amidships in Oil Carriers 150m or more in length” [7]. The ABS guidance describes the FE model and approach for the specific shape of the vessel in way of the foremost cargo tank and fore peak structure, as well as the aftermost cargo tank and forward end of this cargo tank, as shown in figure 2 below.
Figure 2. A typical ABS Guide FEA model of the aftermost and foremost cargo tanks where the critical areas required to be derived
3. 3.1
Figure 1: Behaviour of openings in double bottom ballast tanks with and without ring stiffeners
SOLAS II-1/Reg. 3-6/4.2 requires that the ship’s
structure access manual provides identification of the “critical structural areas”. These are defined as locations that have been identified by “advanced calculation techniques” (as per IACS UI SC191 [6]). PMA applies to cargo tanks, ballast tanks, and other spaces where the critical areas have specific survey requirements and
A-244 CONSTRUCTION. SURFACE PREPARATION
One of the major coating problems that was evident during inspections of older ships was the breakdown of coatings and the subsequent corrosion of cut edges and welds. The introduction of the recent PSPC regulations in ballast tanks now requires that all edges are rounded to a radius of 2mm and that stripe coats are applied to significantly build up the thickness of paint on the edges.
This has resulted in significantly improved preparation standards for edges and welds and has allowed more effective coating applications to occur.
©2011: The Royal Institution of Naval Architects
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