What Is RINA D36 Steel Plate?
RINA D36 is a high strength shipbuilding steel plate approved by the Italian classification society RINA for hull and offshore construction. The grade symbol carries two pieces of information: the letter D defines the impact test temperature of -20 °C, and the number 36 indicates the strength level, historically 36 kgf/mm² and now expressed as a minimum yield strength of 355 MPa. The same strength and toughness combination appears in the IACS unified requirements for higher strength shipbuilding steels, which is why D36 plate from different classification societies can often be cross approved.
The plate is used where ordinary grade A or B hull steel would need excessive thickness. By raising the yield strength to 355 MPa, designers reduce section size, save steel weight and increase deadweight capacity without losing the notch toughness that a ship structure needs in cold water and heavy seas.
Chemical Composition of RINA D36
The table lists maximum ladle analysis values that apply to RINA D36 plate. The chemistry is deliberately lean, with low carbon and low sulphur, so that the plate can be welded with conventional shipyard procedures while keeping the heat affected zone sound.
| Element | Value % | Element | Value % |
|---|---|---|---|
| C | 0.180 max | Nb | 0.02-0.05 |
| Si | 0.10-0.50 | Ni | 0.400 max |
| Mn | 0.90-1.60 | Ti | 0.020 max |
| P | 0.035 max | Cu | 0.350 max |
| S | 0.035 max | Mo | 0.080 max |
| Al | 0.015 min | Cr | 0.200 max |
| V | 0.05-0.10 |
Two formulae are used to control weldability. Crack sensitivity is assessed through the parameter Pcm = C + Si/30 + Mn/20 + Cu/20 + Ni/60 + Cr/20 + Mo/15 + V/10 + 5B, and the carbon equivalent follows Ceq = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15. Both are calculated in percent and are checked against the limits of the applicable shipbuilding rule.
Mechanical Properties and Impact Testing
Yield and tensile requirements are constant across the normal shipbuilding thickness range, while the minimum absorbed impact energy rises with thickness because the through-thickness cooling rate changes during rolling and heat treatment.
| Thickness (mm) | Minimum yield (MPa) | Tensile (MPa) | Elongation (%) | Impact test temperature | Minimum longitudinal energy (J) |
|---|---|---|---|---|---|
| 8-50 | 355 | 490-620 | 21 | -20 °C | 34 |
| 51-70 | 355 | 490-620 | 21 | -20 °C | 41 |
| 71-100 | 355 | 490-620 | 21 | -20 °C | 50 |
Impact testing is carried out on Charpy V-notch specimens taken in the longitudinal direction. Because the D grade is certified at -20 °C, the plate is accepted for hull structures that operate in cold climates and for structural members where brittle fracture would be unacceptable.
Heat Treatment and Delivery Condition
RINA D36 may be supplied in a normalized, normalized plus controlled rolled, thermomechanically processed or quenched and tempered condition, depending on thickness and on what the approved manufacturing procedure allows. Normalizing improves toughness and weldability and is the traditional route for plate rolled from the as-rolled condition, while quenching and tempering raises strength and hardness and allows heavier sections or higher design stresses. The delivery condition must be stated on the inspection certificate, because subsequent hot forming or welding procedure qualification depends on it.
Main Applications
Hull structures: shell plating, decks, inner bottoms and bulkheads of sea going vessels.
Ship structural details subject to high local stress, such as hatch coamings, brackets and foundations.
Offshore platforms, pontoons and floating production units, where low temperature toughness and corrosion resistance are both required.
Marine engineering equipment including cranes, davits and deck machinery.
General structural fabrication for freshwater and marine environments.
Because the grade is approved by a classification society, the plate is normally delivered with a works certificate endorsed for hull use and, when requested, with a society stamp for the specific hull structure class.
Frequently Asked Questions
Q: What does the letter D in RINA D36 mean?
The letter D indicates that the impact test temperature of the grade is -20 °C, while 36 indicates the minimum yield strength level of 355 MPa.
Q: What is the minimum yield strength of RINA D36?
The minimum yield strength is 355 MPa for plate from 8 mm up to 100 mm thickness, with a tensile strength range of 490-620 MPa and a minimum elongation of 21 %.
Q: What impact energy does RINA D36 require?
Minimum longitudinal Charpy V-notch energy is 34 J for 8-50 mm plate, 41 J for 51-70 mm plate and 50 J for 71-100 mm plate, all tested at -20 °C.
Q: How is RINA D36 delivered?
It can be supplied normalized, normalized plus controlled rolled, thermomechanically processed or quenched and tempered depending on thickness and the approved manufacturing route.
Q: Which formulae control weldability?
Crack sensitivity is controlled through Pcm and the carbon equivalent Ceq, both calculated from the ladle analysis of the plate and checked against the applicable shipbuilding rule.
Q: Where is RINA D36 plate used?
It is mainly used for hull plating, decks, bulkheads and structural details of ships, as well as offshore platforms and marine deck equipment.
