ABS B and ABS E are two of the four ordinary-strength hull structural steel grades (A, B, D, E) defined in the ABS Rules for Materials and Welding (Part 2), Chapter 1, Section 2, and in IACS W11, the common rule that all IACS member societies apply to shipbuilding steel. Both plates are certified by the American Bureau of Shipping (ABS) and carry the same strength requirements. The property that separates them is Charpy V-notch impact toughness, measured at different test temperatures. This article explains the verified rule values, the chemical and metallurgical reasons behind them, and how to select between the two grades for a given hull application.
The Core Difference: Charpy V-Notch Impact Test Temperature
Impact testing measures a plate's resistance to brittle fracture. The test temperature is set to match the coldest service condition the steel may see. Under ABS 2-1-2/Table 4, the four ordinary-strength grades are tested at the following temperatures:
Grade A - no impact test for plates up to 50 mm; for thicker plates a 20°C test applies unless the material is fine-grain treated and normalized (ABS 2-1-2/Table 4, Note 3).
Grade B - Charpy V-notch test at 0°C.
Grade D - Charpy V-notch test at -20°C.
Grade E - Charpy V-notch test at -40°C.
Grade B is therefore a general-purpose grade for ambient-temperature service, while Grade E is the toughest ordinary-strength grade and is specified where the structure must absorb impact energy at -40°C. Because -40°C sits far below the typical service range of most merchant ships, Grade E covers polar and ice-class operations with a wide safety margin.
It is important to correct a common misunderstanding: Grade B does have a specified impact test requirement. The 0°C test applies whenever Grade B plate is required to be impact tested under ABS 2-1-2/Table 5, and IACS W11 Table 6 states that Charpy tests are generally not required only for Grade B plates 25 mm thick or less. ABS additionally waives impact tests for plates under 6 mm (2-1-1/11.11). In practice, this means a 40 mm killed Grade B plate is Charpy tested at 0°C, exactly as a 40 mm Grade E plate is tested at -40°C - the difference is only the temperature.
ABS A, B, D and E Ordinary-Strength Grades at a Glance
| Grade | Impact test temperature | Average energy, t ≤ 50 mm (longitudinal / transverse) | Deoxidation and condition of supply | Typical applications | Marking |
|---|---|---|---|---|---|
| A | 20°C (plates over 50 mm only; none for t ≤ 50 mm) | - (t ≤ 50 mm); 34/24 J (50–70 mm); 41/27 J (70–100 mm) | Killed or semi-killed; any condition up to 50 mm | Secondary structures and members in mild service | AB/A |
| B | 0°C | 27/20 J | Killed or semi-killed; any condition up to 50 mm | General hull structures, inner hulls and deck members in temperate routes | AB/B |
| D | -20°C | 27/20 J | Killed; fine-grain treated over 25 mm; normalized, controlled rolled or TMCP over 35 mm | Shell plating and higher-stress members in moderate cold service | AB/D |
| E | -40°C | 27/20 J | Killed and fine-grain treated; normalized or TMCP up to 100 mm | Critical members, ice-going vessels, polar and low-temperature service | AB/E |
Chemical Composition: ABS Grade B vs Grade E
| Element (max. %, unless noted) | ABS Grade B | ABS Grade E |
|---|---|---|
| Carbon (C) | 0.21 | 0.18 |
| Manganese (Mn), min. | 0.80 (1) | 0.70 |
| Silicon (Si) | 0.35 | 0.10–0.35 (2) |
| Phosphorus (P) | 0.035 | 0.035 |
| Sulfur (S) | 0.035 | 0.035 |
| Carbon + Mn/6 | 0.40 | 0.40 |
| Deoxidation | Killed or semi-killed (killed over 50 mm) | Killed and fine-grain treated at all thicknesses |
Mechanical Property: ABS Grade B vs Grade E
| Property | ABS Grade B | ABS Grade E |
|---|---|---|
| Minimum yield strength (N/mm²) | 235 | 235 |
| Tensile strength (N/mm²) | 400–520 | 400–520 |
| Minimum elongation, A5 (%) | 22 | 22 |
| Charpy V-notch test temperature | 0°C | -40°C |
| Avg. energy, t ≤ 50 mm (J, long. / trans.) | 27 / 20 | 27 / 20 |
| Avg. energy, 50 < t ≤ 70 mm (J, long. / trans.) | 34 / 24 | 34 / 24 |
| Avg. energy, 70 < t ≤ 100 mm (J, long. / trans.) | 41 / 27 | 41 / 27 |
ABS B or ABS E: How to Choose
Selection follows the operating temperature of the structure and the consequence of a brittle failure. Work through these criteria in order:
- Service temperature. If the hull structure is designed for a minimum service temperature at or above 0°C, Grade B is sufficient. Any design that sees sub-zero temperatures - ballast water at high latitudes, ice-strengthened hulls, polar or Arctic service - requires Grade D (-20°C) or Grade E (-40°C).
- Structural criticality. Grade E is specified for critical members where a fracture would propagate into a major failure: bottom and side shell in ice zones, stringers and girders in the bow region, and connections in high-stress areas. Grade B is used for general hull structure, inner hulls, decks and secondary members where the risk of brittle fracture is low.
- Classification and ice class. Vessels built to ice classes or polar codes (for example IACS Polar Class or ice-strengthened notations) require the lower impact temperatures. The class rules will state the grade; Grade E is the ordinary-strength grade that satisfies the -40°C requirement.
- Thickness and supply condition. Plates over 50 mm in Grade B must be normalized, controlled rolled or TMCP (ABS 2-1-2/Table 5). Grade E is always killed and fine-grain treated and is supplied normalized or TMCP up to 100 mm, which gives more stable through-thickness properties.
- Cost and lead time. Grade E commands a higher price because of the tighter composition, mandatory grain refinement, normalized/TMCP processing and piece-by-piece impact testing. Grade B is the economical choice whenever the design temperature permits it.
- Welding. Both grades are readily weldable with normal shipyard procedures. The lower carbon of Grade E gives a small additional margin against hydrogen-induced cracking in thick-section welds, but preheat decisions are still driven by thickness, restraint and consumables.
As a rule of thumb: if a specification calls for Grade B and the service temperature is ambient, buy Grade B. If the service temperature can fall below 0°C, or the member is critical in an ice-class hull, specify Grade E. Upgrading Grade D to Grade E is also common practice where the supply chain prefers a single grade, because Grade E meets every Grade D requirement plus the -40°C test.
Certification, Marking and Traceability
ABS-certified plates carry the stamping AB followed by the grade - AB/B for Grade B and AB/E for Grade E (ABS 2-1-2/13.1). Each plate is traceable to its heat through the mill test certificate, which records the ladle analysis, tensile results, impact results and the condition of supply, and is issued under ABS survey. Steel is produced only at works approved by ABS for the grade and thickness supplied; the approval procedure is set out in ABS Part 2, Appendix 4.
Because ABS and the China Classification Society (CCS) both apply IACS W11, the grade system is identical across the two societies: ABS Grade E corresponds to CCS E, tested at the same -40°C with the same 27/20 J acceptance values, and the same correspondence holds for Grades A, B and D. Plates for vessels classed by CCS are commonly supplied with CCS certificates, and dual ABS + CCS certification is available from most mills when a project is to be classed by both societies. When ordering, confirm with the mill that the certificate society, grade and impact temperature match the class notation on the vessel drawings.
FAQ
1. Which grade is tougher, ABS B or ABS E?
Grade E. Both grades must absorb the same energy (27 J average longitudinal for plates up to 50 mm), but Grade E must do so at -40°C while Grade B is tested at 0°C. Grade E is produced with a lower carbon limit, killed and fine-grain practice, and normalized or TMCP supply, which together provide the low-temperature toughness.
2. Does ABS Grade B require a Charpy impact test?
Yes, when the test is required by the supply condition. ABS 2-1-2/Table 4 specifies the 0°C test for Grade B, and Table 5 defines when it applies. Exemptions are limited: plates 25 mm thick or less are generally not impact tested (IACS W11 Table 6, Note 4), plates under 6 mm are exempt (ABS 2-1-1/11.11), and semi-killed Grade B up to 50 mm is supplied without impact testing (ABS 2-1-2/Table 5).
3. What impact energy must ABS E plate meet at -40°C?
For plates up to 50 mm thick, the average absorbed energy is 27 J longitudinal or 20 J transverse; for 50–70 mm it is 34/24 J, and for 70–100 mm it is 41/27 J (ABS 2-1-2/Table 4). One individual test value may be lower than the average provided it is at least 70% of the required average.
4. Is ABS E the same as CCS E?
Yes. Both societies apply IACS W11 to ordinary-strength hull structural steel, so CCS E is tested at -40°C with the same chemical, tensile and impact requirements as ABS E. The marking differs (AB/E vs CCS E), and the certificate must be issued by the society that will class the vessel.
5. Why is ABS E more expensive than ABS B?
Grade E requires a tighter carbon limit (0.18% max vs 0.21%), killed and fine-grain deoxidation at all thicknesses, normalized or TMCP supply, and impact testing on every piece (ABS 2-1-2/Table 5). Each of these steps adds mill cost, which is why Grade E is ordered only where the design temperature makes it necessary.
