Brittle crack arrest steel plates with a thickness of 100mm used in ultra-large container vessels (ULCVs) must have a minimum required brittle crack arrest toughness value (Kca) of 8,000 N/mm3/2 or more at -10°C, according to data issued by Japanese classification society ClassNK.
In order to clarify the required brittle crack arrest toughness value (Kca) for extremely thick steel plates exceeding 80mm, ClassNK carried out a research through a joint R&D project in collaboration with Japan Welding Engineering Society (JWES).
The results were obtained through verification tests by ultra-large-scale test specimens simulating the actual construction of the hatch side coaming and upper deck of ultra-large container ships.
Based on these results, and as part of its response to the ever-increasing size of the design and construction of container vessels, ClassNK said that it will require brittle crack arrest steel plates with a thickness of more than 80mm and not exceeding 100mm to have a brittle crack arrest toughness value (Kca) of 8,000 N/mm3/2 or more at -10°C, as the severest conditions.
IACS released its Unified Requirements on brittle crack arrest design for the use of extremely thick steel plates in January 2013 to enhance the structural reliability of large container vessels, outlining the necessary measures to be taken for the prevention of brittle crack propagation in the event of occurrence of a crack.
The requirements state that brittle crack arrest steel plates with a thickness of 80mm or less must have a brittle crack arrest toughness value (Kca) of 6,000 N/mm3/2 or more at -10°C. However, as there are no specific rules for cases where the thickness of brittle crack arrest steel exceeds 80mm, the required Kca value is to be specifically agreed with each Classification Society.