RINA DH32 Shipbuilding Steel Plate

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

RINA DH32 takes the 32 strength level down to −20 °C toughness. RINA Part D lists it among the higher-strength hull steels with the IACS designation unchanged. Level 32 is the entry high-tensile level. It is popular on ferries and superyachts, where a modest strength gain over mild steel trims weight high up in the ship without changing welding practice much. Minimum yield is 315 N/mm², tensile 440–590 N/mm², elongation 22 %.

Equivalent grades: ASTM A131 Grade DH32 · ABS DH32 · DNV NV D32 · LR DH32 · BV DH32 · CCS D32 / DH32 · NK KD32 · KR RD32 · GB 712 Grade DH32.

In RINA’s high-tensile series the letter sets the Charpy temperature (AH 0 °C, DH −20 °C, EH −40 °C, FH −60 °C) and the number sets the yield (32 → 315, 36 → 355, 40 → 390 N/mm²). DH32 is the D letter at level 32. Typical RINA-classed uses: thick bottom and keel strakes, sheer strakes and stringers of passenger ships, ro-ro side shell and naval-auxiliary hulls that need −20 °C.

RINA is the Genoa-based society that classes much of the Italian fleet and a large share of the world’s cruise ships and ferries, many of them built at Fincantieri and other Italian and Mediterranean yards. That background shows in the steel: passenger ships use large areas of thin plate in decks and superstructure, so flatness, weld distortion and consistent supply count as much as the grade letter.

SHH STEEL supplies DH32 from Chinese mills whose RINA approval covers high-tensile hull steel in the ordered condition and thickness, with the RINA survey at the mill. Common 36-level sizes are held in stock; the rest is rolled to order.

How RINA names it. For higher-strength steel RINA uses the IACS form: H for high tensile, the toughness letter in front and the strength level behind, so DH32 = letter D, level 32. Buyers sometimes shorten it to “D32”, but on RINA paperwork the H stays.

Level 32 gives about a third more yield than mild steel at a small price premium, and its weldability is close to mild steel, so it is an easy first step for yards moving superstructure or ferry decks to high-tensile.

Traded DH32 is usually 6–60 mm thick and 2000–3000 mm wide. Passenger-ship hulls use a lot of 8–20 mm plate in this grade, which most RINA-approved mills roll routinely.

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.

Ladle limits are the IACS UR W11 values for higher-strength hull steel, applied by RINA in Part D (not checked against a RINA edition — UNCERTAIN). Mills often melt DH and EH from the same heat and sort plates by impact results; the certificate must show the grade actually certified, not the heat’s best case.

For TM plate ask for Ceq on the certificate, and Pcm too if your welding procedure is qualified on it. At level 32, most mills reach the strength with Nb alone. Check-analysis tolerances are agreed case by case.

Flat 200 mm test pieces — minimum elongation by thickness:

AH32, DH32, EH32 and FH32 share these tensile values; only the Charpy temperature and, for FH, the chemistry differ. Compared with mild steel, DH32 gives 80 N/mm² more yield, which is the margin the designer spends on thinner 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 TM plate, a yield/tensile ratio is often around 0.8–0.9; there is no class limit unless the order adds one (indicative).

Required energy rises with thickness: a 70–100 mm DH32 plate must average 46 J longitudinal at −20 °C, against 31 J up to 50 mm. DH plate is normally N or TM; as-rolled DH is limited to thin gauges by the supply table.

Condition of supply sets batch size and test frequency, so it belongs on the order. If the owner’s specification adds strain-aged impact tests or Z-direction properties, those are extra requirements and must be priced and booked in advance.

The minus tolerance follows IACS UR W13 as RINA applies it; plus tolerance, flatness and dimensions follow the agreed standard (EN 10029 or GB/T 709). Weight-optimised high-tensile designs — and passenger ships are among the most weight-sensitive — leave little margin, so measure thickness at several points on receipt. Thin high-tensile deck plate distorts more easily during welding than thicker plate; ordering a tighter flatness class can save fairing work later.

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 RINA passenger-ship work we suggest stating both the minus tolerance class and the flatness class on the order for any plate under 10 mm.

Quantities change weekly — confirm before booking. Plates are sold as RINA DH32 with the RINA mark and endorsed certificate. Anything outside the stock list goes into the next mill campaign: about 4–6 weeks to certified plate.

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 DH32 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 of these share the UR W11 DH32 requirements. Each society accepts only its own mark, so if you need RINA plus a second society, book both surveyors before the plates are tested.

Think of the series as a grid: moving right (AH32, DH32, EH32, FH32) lowers the test temperature, moving down (DH32, DH36, DH40) raises the yield. The RINA material class table fixes the letter from structural category and thickness; the scantling calculation fixes the number. Substituting a higher letter at the same number is normally accepted; a lower letter is not.

DH32 is the usual grade for the thick bottom and sheer strakes that the class table promotes from AH. It costs little more than AH and much less than EH. Above 390 N/mm², RINA’s extra-high-strength series starts at D420 (IACS UR W16). See RINA Steel Plates.

Level 32 is often chosen for thinner upper decks and superstructure fronts where buckling, not yield, governs, so the full 355 N/mm² of level 36 would not be used.

Typical uses: thick bottom and keel strakes, sheer strakes and stringers of passenger ships, ro-ro side shell and naval-auxiliary hulls that need −20 °C.

Welding: use RINA-approved high-tensile consumables of grade 3Y or higher (typical UR W17 mapping — confirm in the WPS). Preheat and heat input follow the RINA-approved procedure and the Ceq on the certificate. High-heat-input electrogas or one-side submerged-arc welding of thick DH32 needs a procedure qualified at that heat input.

Forming: TM plate gets part of its strength from controlled rolling and cooling. Keep line heating within the mill’s temperature limit — typically quoted around 650 °C for accelerated-cooled plate (UNCERTAIN, mill-specific).

Why the D letter here. DH32 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 DH32 plates physically separated and colour-marked in the yard so that a lower letter is never fitted by mistake.

The certificate lists ladle chemistry including microalloys, Ceq for TM plate, tensile results, Charpy results at −20 °C, condition of supply and plate numbers, with the RINA surveyor’s endorsement.

On receipt: check the stamp reads DH32 with the RINA mark, the Charpy temperature and thickness band match the plate, and the endorsement is present. We can add EN 10204 3.2 witness, UT to EN 10160 or ASTM A578, Z-direction tests and dual class with another IACS society.

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 DH32, 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 only “DH32” without RINA, so the plate arrives with another society’s mark
• Leaving the letter off (“36 grade”), so toughness is undefined
• Accepting a normal-strength A/B/D/E certificate against a high-tensile order
• No Ceq on the certificate for TM plate
• Substituting AH32 without class approval
• Charpy band for the delivered thickness not checked

A clear order line — grade, rule book, condition, certificate — prevents nearly all of them.

With DH32 the expensive errors are mixed letters within a delivery, missing Ceq for TM plate, and plates whose thickness falls into a higher Charpy band than the test covered.

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 DH32, condition of supply, sizes and quantities, UT / Z-direction, dual class, certificate type and port, and send to SHH STEEL.

Sample line: “Hull plate to RINA Rules for the Classification of Ships, Part D, grade DH32, TM, 12 × 2500 × 12000 mm, 40 pcs, RINA-endorsed certificate with Ceq, EN 10204 3.2, CFR Monfalcone.”

Order checklist:

• Society and rule book: RINA Rules for the Classification of Ships, Part D
• Grade: DH32
• Condition of supply (AR / N / TM as allowed)
• 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 DH32 is higher-strength hull steel under RINA’s Rules for the Classification of Ships, Part D (Materials and Welding): yield 315 N/mm², tensile 440–590 N/mm², Charpy −20 °C. A RINA-classed ship accepts it only with the RINA mark and an endorsed certificate.

SHH STEEL supplies RINA DH32 from RINA-approved Chinese mills, with cutting, UT and EN 10204 3.2 on request. Send grade, sizes, quantities and port for a quotation.