Differences Between DNV Grades AH36, DH36, and EH36

I. Meaning of Grade Designations (DNV Naming Conventions)

A/D/E: Low-temperature toughness quality grades, corresponding to progressively lower impact test temperatures

H: High Strength

36: Minimum yield strength of 355 MPa (36 kgf/mm²)

The tensile strengths of these three grades at room temperature are identical; the only key differences lie in the low-temperature Charpy impact toughness thresholds, smelting purity, and minimum service temperatures.

II. Differences in Chemical Composition

The base carbon, manganese, and silicon ranges for DNV Grades AH36, DH36, and EH36 are similar; differences are primarily in impurity control, microalloying, and nickel content:

1. DNV Grade AH36

P ≤ 0.030%, S ≤ 0.030%; upper limits for impurities are lenient;

Niobium, vanadium, and titanium microalloying are not mandatory; steel mills may add them as needed;

No mandatory nickel content; lowest cost.

2. DNV Grade DH36

P ≤ 0.025%, S ≤ 0.025%; stricter impurity limits;

Trace amounts of Nb/V/Ti must be added for grain refinement;

Small amounts of nickel may be added to improve low-temperature toughness.

3. DNV Grade EH36

P ≤ 0.025%, S ≤ 0.025%; the strictest impurity limits;

Microalloying is mandatory (combined addition of Nb + V/Ti);

Typically contains 0.4%–0.8% Ni, which significantly improves ultra-low-temperature toughness; this grade has the highest alloying cost.

III. Differences in Mechanical Properties

Comparison of Mechanical Properties

Key Differences

IV. Differences in Delivery Conditions

DNV AH36: Thin plates may be delivered in hot-rolled AR condition; thick plates may be delivered in controlled-roll TMCP or normalized N condition, with the lowest process requirements;

DNV DH36: TMCP is preferred for medium- and heavy-gauge plates; heavy-gauge plates typically require normalizing, and plain hot-rolled plates are prohibited;

DNV EH36: TMCP controlled rolling or normalizing is mandatory for the vast majority of cases; critical components made of heavy-gauge plates require quenching and tempering (Q+T); rolling and heat treatment controls are the most stringent.

V. Differences in Applicable Scenarios and Sea Areas

1. DNV Grade AH36 (NV A36)

Applications: Bulk carriers, container ships, and general oil tankers operating in warm, ice-free waters year-round.

Locations: Upper decks, general ribs, non-waterline secondary bulkheads, and inner bottom plates.

Restrictions: Not for use in seawater areas where temperatures are consistently below 0°C, polar vessels, the main structures of LNG carriers, or the primary load-bearing structures of offshore platforms.

2. DNV Grade DH36 (NV D36)

Applications: Vessels operating in the North Pacific, North Atlantic, and waters with low winter temperatures; conventional offshore platforms.

Locations: Above-waterline outer plates, bottom hull plates, main deck, ballast tanks, and secondary components of medium-sized offshore engineering structures;

Features: Balances strength with low-temperature toughness at -20°C; the most widely used general-purpose high-strength ship plate on the market.

3. DNV Grade EH36 (NV E36)

Applications: Polar-class vessels, ice-strengthened vessels, offshore wind power platforms, FPSOs, and LNG auxiliary structures;

Locations: Ice-zone outer plates, crane bases, thick side plates, critical high-strength joints, and submersible load-bearing components;

Features: Maintains high toughness even at -40°C, eliminating the risk of low-temperature cracking; mandatory for ice-class vessels.

VI. Procurement and Cost Differences

Cost Ranking: AH36 < DH36 < EH36

DNV AH36: Low smelting requirements, relaxed impurity limits, simple rolling process, ample market supply, and the lowest unit price.

DNV DH36: Additional desulfurization and dephosphorization processes; narrower controlled rolling window; slightly higher price.

DNV EH36: Low impurities + nickel alloy + precision TMCP rolling; more inspection items (higher proportion of batch sampling for low-temperature impact testing); highest price; longer delivery lead time.