Difference between ABS DQ51 and CCS DQ51

ABS DQ51 and CCS DQ51 are both extra-high-strength quenched and tempered steel plates specifically designed for the most demanding marine and offshore engineering applications. They are certified by two major classification societies-ABS (American Bureau of Shipping) and CCS (China Classification Society)-and represent a higher strength tier within the DQ series, offering enhanced low-temperature toughness suitable for critical structural components.

ABS Grade DQ51 is certified by the American Bureau of Shipping. The designation "DQ51" indicates it is an extra-high-strength steel with a minimum yield strength of 500 MPa and a tensile strength range of 610-770 MPa . The "D" signifies the impact test temperature of -20°C, requiring minimum Charpy V-Notch impact energy of 50J (longitudinal) or 33J (transverse) . These plates are manufactured using advanced heat treatment processes such as quenched and tempered (QT) , normalizing, or thermomechanical control processing to achieve their exceptional combination of strength and toughness . Typical applications include offshore drilling platforms, shipbuilding, hull structures, decks, superstructures of large vessels, FPSOs, and critical marine structures operating in cold environments .

CCS Grade DQ51 is certified by the China Classification Society and serves as the direct equivalent to ABS DQ51 in the Chinese classification system . According to classification society standards, CCS DQ51 shares identical mechanical property requirements with its ABS counterpart: minimum yield strength of 500 MPa and tensile strength of 610-770 MPa . It belongs to the same product family as AQ51, DQ51, EQ51, and FQ51 series for shipbuilding and offshore applications, with each letter representing a different impact test temperature . Like ABS DQ51, CCS DQ51 requires Charpy impact testing at -20°C with minimum energy requirements consistent with ABS standards.

Key Differences:
The primary distinction between these two grades lies in their certifying authority and the corresponding quality control system . ABS DQ51 complies with American Bureau of Shipping rules and is recognized internationally, particularly in projects requiring ABS certification for offshore platforms and vessels destined for ABS-classed fleets. CCS DQ51 complies with China Classification Society rules and is typically specified for offshore structures built in Chinese shipyards or for projects under Chinese classification. From a technical perspective, these steels are considered interchangeable, and major manufacturers can produce plates certified by both societies simultaneously.

Chemical Composition

Mechanical Property

CCS DQ51 Extra high strength property in tempering and quenching