Kazukuni Hase

Offshore Structural Steel Plates for Extreme Low Temperature Service With Excellent HAZ Toughness

The strength and the toughness required for steel plates used for offshore structures became higher as the installation areas move into arctic areas. The main property of offshore structure steel is the crack tip opening displacement (CTOD) property of weld joint, and CTOD testing is performed at the minimum design temperature of the structure. Thus, the demand for satisfying −40°C of CTOD test temperature specification has increased. For the improvement of HAZ toughness, coarse austenite grain is suppressed by TiN, and low-C, Ceq, Si, P, Nb design is adopted to decrease the formation of M-A constituents. Furthermore, by using Ca inclusion, which works as a pinning particle and a bainite nucleation site, very fine bainite microstructure are formed in HAZ and excellent low temperature toughness are achieved. The YP420 class plate with excellent low temperature toughness has been developed using these technology.Copyright

Steel Plates With Excellent HAZ Toughness for Offshore Structure

In the field of offshore structure, the strength and the toughness required for steel plates used for oil resource development become higher as the installation areas of the structures move into arctic and deep water areas. High strength steel plates for offshore structures, which meet the low temperature specification, have been developed. Excellent properties of the steel plates have been achieved by micro-alloying, the latest controlled rolling and accelerated cooling technology. Excellent properties of weld joints have been also achieved by advanced metallurgical techniques, which are grain-refinement of the coarse grain heat affected zone (CGHAZ), reduction of Martensite-Austenite (M-A) constituent in inter-critically CGHAZ (ICCGHAZ), and improvement of the matrix toughness. These steels are designed for excellent weldability due to low weld cracking parameter (PCM) value up to 550 MPa class in yield stress, and also up to 101.6 mm in thickness with 420 MPa class in yield stress, and satisfying −40°C of crack tip opening displacement (CTOD) temperature specification for offshore structure.Copyright