Although experts say that the evolution of bigger containerships is in principle technically possible, the new developments may lead to[ds_preview] new safety standards. Japanese classification society ClassNK has therefore announced it will carry out a joint research project aimed at improving existing standards for ultra-large container ships. As container ships increase in size, so too does the thickness of the steel that is used. The preventative measures for brittle fracture become even more important with thicker steel especially in areas where higher stress occurs such as the upper deck and hatch side coaming of the cargo holds, ClassNK states. In light of this and to improve the safety standards of large container vessels, International Association of Classification Societies (IACS) released its »Unified Requirements for Use of Extremely Thick Steel Plates« in January 2013. The requirements outline the necessary measures to be taken for the prevention of brittle crack propagation in the block-to-block butt joints of the hatch side coaming and upper deck to prevent large scale fracture of the hull girder.
One of the preventative measures is the use of brittle crack arrest steel, defined as steel with measured crack arrest properties. However, the IACS requirements apply only to brittle crack arrest steel plates with a thickness of up to 80mm. Where the thickness of these steel plates exceeds 80mm, the crack arrest parameter must be specifically agreed with each classification society.
With the introduction of 20,000TEU vessels, ClassNK expects an increased use of brittle crack arrest steel exceeding 80mm in thickness. To ensure smooth adoption of thicker steel in the industry, the society has embarked on a joint research project to develop technical standards in order to clarify the crack arrest parameter for steel plates exceeding 80mm. Through this joint research, ClassNK aims to establish clearer evaluation methods to form the proposal for unified IACS requirements for brittle crack arrest steel exceeding 80mm for the benefit of the entire maritime industry.
The project will be carried out as part of the ClassNK Joint R&D for Industry Program in collaboration with the Japanese Welding Engineering Society (JWES), steel manufacturers, shipbuilders, and neutral research institutes, and is scheduled to be completed in mid-2016.
