Choosing between RINA DH460 and DH550 comes down to one question: how much load must the plate carry for a given weight? Both are extra-high-strength marine steel plates certified by RINA (Registro Italiano Navale) and manufactured to IACS Unified Requirement W16, "High Strength Steels for Welded Structures."
RINA adopts the IACS grade system for extra-high-strength hull and offshore steels. The letter in the grade marks the Charpy V-notch impact test temperature: grade D is tested at -20°C (grade E at -40°C, grade F at -60°C). The number states the minimum yield strength in MPa. "RINA D460" therefore stands for a steel with a guaranteed minimum yield strength of 460 MPa that has proven impact toughness at -20°C; the formally correct designation is DH460, where H denotes high strength. Many suppliers, including this site, use the shorter D460/D550 form. What the two grades share is the -20°C toughness requirement; what separates them is the strength level and, with it, the alloying strategy, the permitted delivery conditions, and the price.
Chemical Composition and Carbon Equivalent: RINA D460 vs RINA D550
| Element (max %, ladle analysis) | RINA DH460 (D460) | RINA DH550 (D550) |
|---|---|---|
| Carbon (C) | 0.20 (N/NR); 0.18 (TM/QT) | 0.18 (TM); 0.18 (QT) |
| Manganese (Mn) | 1.00 - 1.70 | 1.00 - 1.70 |
| Silicon (Si) | 0.60 | 0.60 (TM); 0.80 (QT) |
| Phosphorus (P) | 0.030 (N/NR); 0.025 (TM/QT) | 0.025 (TM); 0.025 (QT) |
| Sulphur (S) | 0.025 (N/NR); 0.020 (TM/QT) | 0.020 (TM); 0.020 (QT) |
| Niobium (Nb) / Vanadium (V) / Titanium (Ti) | 0.05 / 0.20 (N/NR) or 0.12 (TM/QT) / 0.05 | 0.05 / 0.12 / 0.05 |
| Nickel (Ni) | 0.80 | 0.80 |
| Copper (Cu) / Chromium (Cr) / Molybdenum (Mo) | 0.55 / 0.30 (N/NR) or 0.50 (TM) / 0.10 (N/NR) or 0.50 (TM) | 0.55 (TM) or 0.50 (QT) / 0.50 / 0.50 (TM) or 0.70 (QT) |
| Total aluminium (min) | 0.02 | 0.02 |
| Nitrogen (N) | 0.025 | 0.025 (TM); 0.015 (QT) |
| Carbon equivalent CEV (IIW), max | 0.50 (N/NR, t≤50); 0.45 (TM); 0.47 (QT) | 0.48 (TM); 0.56 (QT) |
| Pcm (cold cracking susceptibility), max | 0.25 (N/NR); 0.23 (TM); 0.24 (QT) | 0.25 (TM); 0.28 (QT) |
Mechanical Properties: RINA D460 vs RINA D550
| Mechanical Property (per IACS UR W16) | RINA DH460 (D460) | RINA DH550 (D550) |
|---|---|---|
| Minimum yield strength (MPa) | 460 | 550 |
| Tensile strength (MPa) | 570 - 720 | 670 - 830 |
| Minimum elongation (%) | 17 | 16 |
| Charpy V-notch impact test temperature (°C) | -20 | -20 |
| Minimum impact energy (J, average of 3) - longitudinal / transverse | 46 / 31 | 55 / 37 |
| Delivery conditions | Normalized (N/NR), TMCP (TM) or QT | TMCP (TM) or QT only |
| Typical plate thickness scope (mm) | up to 250 (N); up to 150 (TM/QT); thicker by class approval | up to 150 (TM/QT); thicker by class approval |
Manufacturing Routes: Normalizing Stops at 460, Not at 550
Delivery conditions follow IACS UR W16. DH460 can be supplied normalized (N) or normalized rolled (NR), thermomechanical controlled processed (TM, i.e., TMCP, with or without accelerated cooling), or quenched and tempered (QT). DH550 - and every grade above 460 MPa - is restricted to TM or QT, because normalizing alone cannot reliably deliver 550 MPa yield strength with adequate toughness in thick plates. Thickness limits also differ: UR W16 sets 250 mm maximum for N plates and 150 mm for TM/QT plates, with thicker plates subject to special approval by the classification society.
Applications and Certification: Where Each Grade Earns Its Place
DH460 is the workhorse of high-stress marine structures where 460 MPa yield is sufficient: hull strength members of large commercial ships, deck and bottom structures, bulkheads, and offshore jacket components. DH550 is selected where weight savings justify the premium: jack-up rig legs and racks, crane pedestals, FPSO turret and mooring structures, and the most heavily loaded hull details of large containerships and offshore support vessels. Both grades are approved for service temperatures down to -20°C through the D-grade impact requirement.
Certification follows RINA Rules for the Classification of Ships (Part B, Hull and Stability, materials requirements), implemented in accordance with IACS Unified Requirements. The steel must be produced at a mill approved by RINA for the specific grade and delivery condition; each plate is supplied with RINA-certified mill test certificates covering ladle analysis, CEV/Pcm, and the required tensile and Charpy tests, with traceability maintained per IACS UR W11 and test procedures per IACS UR W2. Plate thickness tolerances follow IACS UR W13, and through-thickness (Z-quality) requirements, where specified, follow IACS UR W14.
FAQ
1. What does "D" mean in RINA D460 / D550?"D" is the impact toughness grade: the steel must pass Charpy V-notch testing at -20°C. In the same IACS system, E means -40°C and F means -60°C. The numbers 460 and 550 are the minimum yield strengths in MPa.
2. Is "RINA D460" the same as "RINA DH460"?
Yes. DH460 is the formal designation per IACS UR W16 (H = high strength); D460 is the widely used short form. The same applies to D550 / DH550.
3. What is the impact energy requirement at -20°C?
For plates wider than 600 mm, the requirement is transverse: 31 J for DH460 and 37 J for DH550 (average of three specimens), with longitudinal values of 46 J and 55 J respectively. The plate is tested transverse to the rolling direction.
4. Can DH550 be supplied in normalized condition?
No. Per IACS UR W16, grades above 460 MPa yield (including DH550) are supplied TMCP or quenched and tempered only. Normalized delivery is permitted for DH460.
5. How do the two grades compare for welding?
Both are weldable, but DH550 demands more care: its maximum CEV (0.56 in QT) and Pcm (0.28) are higher than DH460 (0.50 CEV and 0.25 Pcm in N/NR). Welding procedure specifications must set controlled heat input and preheat, typically qualified under the applicable RINA or IACS weldability scheme before production.
6. Which grade should I specify?
Specify DH460 when 460 MPa yield meets the design stress and you want the widest delivery-condition choice and the easiest welding. Specify DH550 when the design allows thinner plate through higher strength - the typical driver is weight reduction on offshore equipment or large vessels - and your fabrication shop can hold the tighter welding parameters.
