RINA D500 Shipbuilding Steel Plate

Technical Reviewer: Jack | SHH STEEL Material Solutions Department · Updated: 2026-10-28

RINA D500 is the −20 °C grade at the 500 N/mm² extra-high-strength level. RINA names its extra-high-strength hull steels in the official form without an “H”: toughness letter A, D, E or F followed by the minimum yield in N/mm², so D500 rather than an AH-style name. They are covered in Part D (Materials and Welding) of the Rules for the Classification of Ships on the basis of IACS UR W16. The 500 level is mainly an offshore and special-vessel level; mainstream merchant hulls rarely go this high.

Equivalent grades: ASTM A131 (no direct grade at this strength) · ABS DH50 / DQ51 · DNV NV D500 · LR DH50 · BV D500 · CCS DH500 · NK KD500 · KR RD51 · GB 712 Grade DH500.

UR W16 values: ReH ≥ 500 N/mm², Rm 610–770 N/mm², A ≥ 16 %, Charpy at −20 °C. The D letter is what the class table usually asks for once the plate gets thick, so it is the most common EHS letter on ship structure.

D500 is produced TM or QT, and only at a mill whose RINA approval names this grade, condition and thickness range. Approval for AH36 or for a lower EHS level does not extend to it automatically.

Extra-high-strength plate is less common on RINA’s core passenger-ship work than AH/DH36, but it appears on the largest ships, on cranes and lifting gear, and widely on offshore and special units classed by RINA.

D500 is rolled to order, not held as open stock. SHH STEEL places the order with a RINA-approved Chinese mill, books the RINA survey, and adds UT, dual class or 3.2 witness on request. Typical uses: offshore units, heavy-lift and special vessels; seldom mainstream merchant hulls.

How RINA names it. For extra-high-strength steel RINA drops the H and writes the yield in full — D500 — which is why the same plate appears as DH500 in IACS UR W16 and some product standards. Both describe the same 500 N/mm² level with −20 °C toughness.

Maximum thickness is set by the mill approval. As a guide, TM D500 is often approved to about 50–80 mm and QT thicker, but the approval certificate is the limit (UNCERTAIN). At this level, most enquiries are 20–100 mm QT plate for offshore and lifting structure.

Product (check) analysis column: RINA Rules Part D specify heat (ladle) limits; no numeric product-analysis tolerance is tabulated in the rule text reviewed, so product (check) limits are agreed on the order or taken from the approved mill specification and certificate.

The table gives the UR W16 envelope. RINA fixes the exact limits for each mill at approval, so the approval document and the order govern (UNCERTAIN against the Part D text). From 500 upward, Ni and Mo become regular additions and the heavier gauges are made QT.

The D letter at this level shares the A/D/E chemistry envelope; the toughness difference comes mainly from process route and steel cleanliness. Every intentionally added element must appear on the certificate together with Ceq, CET or Pcm, because the welding procedure depends on them.

Boron, when added, works in parts per million and is effective only when nitrogen is tied up, usually by titanium; that is why B, Ti and N should be read together on the certificate.

Tests are taken per heat-treatment batch or per rolled length as the approval requires; thick plate may need extra mid-thickness tests. Compared with DH40 the yield rises by 110 N/mm². That gain only pays off if the welded joint keeps up, so check that the qualified procedure reaches matching strength and toughness in weld metal and HAZ, not just in the plate.

Tensile specimens are taken transverse to the rolling direction for plate wider than about 600 mm, as UR W11/W16 practice requires; the certificate should show the specimen orientation. For QT plate, Rp0.2 is often reported instead of ReH because the yield point is not pronounced.

Charpy specimens are normally taken at quarter thickness and tested at −20 °C. Delivery is TM or QT; the choice changes mill, price, flatness and welding behaviour, so state it on the order. QT is the usual route at this level, particularly in thick plate; TM may be possible in thinner gauges where the approval allows.

Strain-ageing or CTOD data are not part of the basic grade; ask for them only if your yard or owner specification requires them.

TM plate gets its strength from controlled rolling and accelerated cooling, so it starts with low carbon and good weldability, but can lose some strength if heated above the mill’s limit. QT plate is austenitised, quenched and tempered, which gives uniform properties in thick sections; the tempering temperature then becomes the ceiling for any later heat treatment.

Minus tolerance follows IACS UR W13; plus tolerance and flatness follow the agreed standard. QT plate is generally flatter than heavy TM plate but harder to straighten afterwards, so agree the flatness class at enquiry. Do not flame-straighten EHS plate above the mill’s stated temperature without approval — it can undo the TM or tempering treatment.

UR W13 also allows local grinding of surface defects and sets how the average thickness of a plate is checked; the measurement points and acceptance method should be agreed at enquiry if the yard has its own procedure. For EHS plate, thickness is usually measured by ultrasonic gauge at the mill and recorded on request; ask for it if the design relies on the minimum thickness.

RINA D500 is not held as open stock. The table shows the thickness and width combinations we most often book into a mill campaign; expect roughly 6–10 weeks from order to RINA-certified plate (commercial estimate).

Packing: bundled by size with steel strapping, marked with grade and heat number, shipped in containers (≤ 11.8 m) or break bulk to Mediterranean and other ports.

Processing before shipping. We cut D500 to drawing by plasma or oxy-fuel, bevel edges for welding, shot-blast and prime with shop primer, and mark each piece with grade, heat number and part number so that RINA traceability survives cutting. Cut parts ship with a cutting list that cross-references every piece to its original plate and certificate.

All sit in the same UR W16 band. The names differ (with or without “H”, R- or K-prefix, LR yield/10 numbers), and only the RINA mark counts for a RINA-classed structure.

Neighbours are D460 below and D550 above. Within level 500 the letter sets the test temperature: A 0 °C, D −20 °C, E −40 °C, F −60 °C. Changing level needs RINA plan approval.

As a rough guide for a yield-governed member, 30 mm of DH40 becomes about 23.4 mm of D500. Buckling, fatigue and corrosion margins often limit the real saving, so the gain is usually smaller (estimate, not a rule value).

Other RINA grades are listed under RINA Steel Plates; offshore-specific grades under offshore platform steel plates.

In RINA practice, EHS grades are usually concentrated in a few highly stressed areas rather than used everywhere. That keeps the number of welding procedures down: the yard only needs D500 procedures for the members where it pays.

Typical uses: offshore units, heavy-lift and special vessels; seldom mainstream merchant hulls.

The yard welds D500 only under a RINA-approved WPS qualified on this grade, using low-hydrogen consumables that reach matching strength and −20 °C toughness in the weld metal. Heat input must be limited to protect HAZ toughness in QT plate, and preheat is usually needed on thick sections. Do not hot-form or stress-relieve above the tempering temperature without agreement from the mill and RINA.

Why the D letter here. D500 is tested at −20 °C and is chosen for thick strakes in temperate service and ships that occasionally trade to colder waters. DH is often the best value grade where the class table and the owner leave a choice between AH and EH. When building blocks mix letters, keep D500 plates physically separated and colour-marked in the yard so that a lower letter is never fitted by mistake.

HAZ softening can occur in TM plate under very high heat input, and HAZ hardening in QT plate under very low heat input, so the qualified range in the WPS should be respected on both sides. Hydrogen control — dry consumables, clean joints and controlled preheat — matters more as strength rises.

The certificate gives full alloy analysis, Ceq/CET/Pcm, tensile results, −20 °C Charpy results, condition of supply, UT result and plate numbers, with the RINA surveyor’s endorsement.

On receipt, check the D500 stamp and RINA mark, impact temperature, UT report and endorsement. Dual class with another IACS society and 3.2 witness are available if booked before testing.

RINA approval of the manufacturer. A mill is approved by RINA for named grades, steelmaking route, delivery condition and maximum thickness, after approval tests and periodic renewal. Before placing an order for D500, ask to see that the approval scope actually lists this grade and condition up to the thickness you need — this is the single most useful check a buyer can make (approval document format UNCERTAIN).

• Writing AH500 instead of the official D500, or leaving out RINA
• Leaving TM vs QT open
• No UT requirement
• Ceq/Pcm not requested
• Ordering from a mill whose RINA approval does not cover the grade or thickness
• Expecting an ASTM A131 dual certificate (none exists at this level)

EHS plate is rolled for you, so a wrong order line costs a full rolling cycle. Check it twice.

With EHS plate the expensive errors are the ones that cannot be fixed after rolling: wrong route, wrong thickness range for the mill approval, or missing UT.

If your yard has never bought from a Chinese mill under RINA survey, we can arrange a trial lot, share sample certificates in advance, and let your inspector or the RINA surveyor visit the mill during rolling and testing.

State RINA D500, TM or QT, sizes and quantities, UT level, dual class, certificate type and port, and send to SHH STEEL.

Sample line: “Plate to RINA Rules for the Classification of Ships, Part D, grade D500, QT, 40 × 2500 × 10000 mm, 8 pcs, UT EN 10160 S1E1, RINA-endorsed certificate with Pcm, EN 10204 3.2.”

Order checklist:

• Society and rule book: RINA Rules for the Classification of Ships, Part D
• Grade: D500
• Condition of supply (TM or QT)
• Sizes and quantity per size; flatness class if tighter than standard
• Certificate: RINA-endorsed, EN 10204 3.1 or 3.2
• Extras: UT, Z-direction, dual class, shot-blast/prime, cutting
• Delivery terms and destination port

RINA D500 is extra-high-strength hull steel under RINA’s Rules for the Classification of Ships, Part D (Materials and Welding): yield 500 N/mm², tensile 610–770 N/mm², Charpy −20 °C. A RINA-classed ship accepts it only with the RINA mark and an endorsed certificate.

SHH STEEL supplies RINA D500 from RINA-approved Chinese mills, with cutting, UT and EN 10204 3.2 on request. Send grade, sizes, quantities and port for a quotation.