Overview of DNV A and DNV B
DNV A and DNV B are standard-strength shipbuilding steel plates certified by Det Norske Veritas. As the foundational grades in the DNV classification system, they are widely used for general structural components in ship hulls and marine applications where extreme low-temperature toughness is not a primary requirement. Both grades possess a minimum yield strength of 235 MPa, with their core distinction defined by their differing impact toughness specifications.
Key Differences in Impact Testing
The key difference lies in the mandatory Charpy V-notch impact test requirement and thus suitability for different structural areas. DNV Grade A steel has no specified impact test requirement; it is intended for non-critical, secondary structures where the risk of brittle fracture is considered low under normal service conditions. DNV Grade B steel is required to meet a defined impact energy value when tested at 0 degrees C. This guaranteed notch toughness makes Grade B significantly more reliable for primary hull structures and other critical components subjected to dynamic loads or incidental stresses.
Chemical Composition
DNV A limits carbon to 0.21 percent with silicon up to 0.05 percent and manganese up to 2.5 times the carbon content. DNV B limits carbon to 0.21 percent, silicon to 0.35 percent, and manganese to 0.80 percent. Both limit phosphorus and sulfur to 0.035 percent each. The composition differences reflect the different toughness requirements of the two grades.
Mechanical Properties
Both grades have a minimum yield strength of 235 MPa, tensile strength of 400 to 520 MPa, and minimum elongation of 22 percent for thicknesses up to 150 mm. For impact testing, DNV A has no requirement for thicknesses up to 50 mm, with 24 J transverse and 34 J longitudinal required for 50 to 70 mm, and 27 J and 41 J for 70 to 150 mm; the temperature is plus 20 degrees C. DNV B requires 20 J transverse and 27 J longitudinal at 0 degrees C for thicknesses up to 50 mm, increasing with thickness.
Applications and Selection
DNV A is chosen for secondary structures, superstructures, and areas with low fracture risk. DNV B is specified for primary hull structures, decks, and components subjected to dynamic loading. The selection is driven by the structural class and the design temperature of the vessel.
Frequently Asked Questions
Q: What is the difference between DNV A and DNV B?
A: DNV A has no mandatory impact test, while DNV B requires guaranteed Charpy impact energy at 0 degrees C.
Q: What is the yield strength of both grades?
A: 235 MPa minimum, with tensile strength of 400 to 520 MPa and elongation of 22 percent minimum.
Q: Where is DNV B required?
A: For primary hull structures and critical components subjected to dynamic loads or incidental stresses.
Q: What is the impact requirement for DNV B at 50 mm thickness?
A: 20 J transverse and 27 J longitudinal at 0 degrees C.
Q: Is DNV A suitable for primary structures?
A: No, it is intended for non-critical secondary structures with low brittle fracture risk.
Q: Do the grades have the same composition?
A: No, DNV B specifies higher silicon and lower manganese limits reflecting its toughness requirements.
For DNV A and DNV B certified shipbuilding plate quotations, contact our sales team.
