The first large sized container carrier in the world to use a new grade of higher tensile steel in its hull structure with a specified yield point of 47 kgf/mm (460N/mm) was built to NK class and delivered in June 2007. Known as YP47 steel, this comparatively strong and tough material is currently attracting much attention as an effective solution to the challenges presented by the use of extremely thick steel plates in the construction of the hull structures of container carriers that have been growing ever larger in size in recent years.
ClassNK prepared these guidelines drawing upon the results of many years of research conducted into the practical application of YP47 steel and the experience gained from actual use of the material in the construction of large size container carriers. The publication sets forth comprehensive technical guidelines on the application of YP47 steel, including specifications on the hull girder strength, fatigue strength and other factors affecting hull structural strength, as well as material specifications and requirements for welding procedures, fabrication and related work carried out during construction. The Guidelines also include provisions on brittle crack arrest design that serve as a backup safety measure for preventing brittle fracture in the event of brittle cracking.
As container carriers continue to grow ever larger in size and effective means are sought to address the related safety concerns accompanying such growth, it is hoped that these guidelines will come to be widely used and thus contribute to enhancing the structural integrity and safety of large and ultra large container carriers now and in the future.
The guidelines can be downloaded from the ClassNK website at www.classnk.or.jp.