ClassNK identifies ULCS steel strength requirements

28 Jul 2016

ClassNK has concluded that 8000 N/mm3/2 is the minimum required brittle crack arrest toughness for extremely thick brittle crack arrest steel plates of 100mm used in ultra-large container ships.

The result is based on verification tests carried out as part of a joint R&D project in collaboration with Japan Welding Engineering Society (JWES).

Back in 2013, IACS released its Unified Requirements on brittle crack arrest design for the use of extremely thick steel plates to enhance the structural reliability of larger container vessels.

It outlined the necessary measures to be taken for the prevention of brittle crack propagation in the event of occurrence of a crack.

The requirements stated that brittle crack arrest steel plates with a thickness of 80mm or less must have a brittle crack arrest toughness value of 6,000 N/mm3/2 or more at -10°C.

But there were no rules for cases where the thickness of brittle crack arrest steed exceeds 80mm, so in order to establish this ClassNK carried out research through the joint industry project with JWES.

Verification tests were carried out by ultra-large-scale test specimens which simulated the construction of the hatch side coaming and upper deck of ultra-large container ships as part of the joint project.

The results revealed for the first time that brittle crack arrest steel plates with a thickness of 100mm must have a brittle crack arrest toughness value (Kca) of 8,000 N/mm3/2 or more at -10°C.

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