Prevention of large-scale brittle fracture inducing hull breakage is extremely important in order to secure the safety of vessels. Meanwhile classification societies specify the arrangement of grades E or EH steel plates as crack arrestor to critical hull structural members such as sheer strake, deck stringer etc. However, the clear arrestability requirement for the crack arrestor is not necessarily specified in the rules of the classification societies.
In this paper, the arrestability requirements for the crack arrestor, which intends for vessels under “normal operation” and “emergency situation” such as collision and stranding, are examined by fracture mechanics (K-concept) . Moreover based on the above examination, the first-ever crack arrestor concept to secure hull structural integrity under “emergency situation” is developed by the classification society.
Then this paper comes to the following conclusions:
(1) For vessels under “normal operation”, it is possible to arrest extremely long brittle crack where Kca value of crack arrestor plate at minimum service temperature (-10°C) secures 6000N⁄ mm1.5and over.
(2) For vessels under “emergency situation”, it is possible to arrest extremely long brittle crack where Kca value of crack arrestor plate with 10% plastic strain at minimum service temperature (-10°C) secures 6000N⁄mm1.5 and over.
(3) As the first-ever crack arrestor concept corresponding to “emergency situation”, the classification society (ClassNK) developed the innovative institution to identify and register the vessels with Descriptive Note “H-ARST” which denotes applying the higher crack arrestor to the specific hull structural members.
