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S355NH steel is a fine-grain structural hollow-section grade with a minimum yield strength of 355 MPa for thicknesses up to 16 mm. Under EN 10210-1 and EN 10219-1, it also requires a minimum average Charpy V-notch energy of 40 J at −20 °C.
The two standards use different manufacturing routes and delivery conditions, so their finished sections are not directly interchangeable. This article compares their mechanical properties, chemical limits and impact-test requirements across the hollow-section shapes covered by each standard.
What Is S355NH Steel?
S355NH is a fully killed, fine-grain, non-alloy quality steel. S means structural steel, 355 is the minimum yield strength in MPa at thicknesses up to 16 mm, and H denotes a hollow section. N has a standard-specific meaning: under EN 10210-1, it denotes a normalized or normalized-rolled finished product; under EN 10219-1, it denotes normalized or normalized-rolled feedstock used to produce the cold-formed section.
The H suffix does not restrict the grade to SHS or RHS. The applicable standard determines which forms are covered; this guide to hollow-section shapes and structural uses explains the common CHS, SHS and RHS terminology.
Which Standards Cover S355NH Hollow Sections?
EN 10210-1 covers hot-finished S355NH sections, while EN 10219-1 covers cold-formed welded sections. Similar strength and impact values do not make the products interchangeable.
| Standard | Manufacturing Route | Thickness Range | Key Difference |
| EN 10210-1 | Seamless or welded; formed hot, or formed cold and subsequently heat treated to equivalent metallurgical conditions | S355NH property tables cover t ≤ 65 mm | The finished product is delivered normalized, including normalized rolled |
| EN 10219-1 | Cold-formed welded section without subsequent section heat treatment; the weld seam may be as-welded or heat treated | S355NH property tables cover t ≤ 40 mm | N applies to the feedstock; the finished section remains cold formed |
These are property-table limits, not guaranteed commercial size ranges.
Under EN 10210. The standard covers circular, square, rectangular and elliptical sections; EN 10210-2 gives dimensions and tolerances. For SHS or RHS projects, the available EN 10210 square and rectangular hollow-section sizes can support an initial dimensional review; S355NH availability must still be confirmed.
Under EN 10219. The standard covers cold-formed welded circular, square and rectangular sections; EN 10219-2 gives dimensions, tolerances and sectional properties.
The following values use the 2006 editions. Orders should identify the required edition and national adoption.
What Are the Mechanical Properties of S355NH Steel?
S355NH has a minimum yield strength of 355 MPa up to 16 mm; the requirement falls at greater thicknesses.
| Property | EN 10210 Requirement | EN 10219 Requirement | Technical Relevance |
| Minimum yield strength, ReH | 355 MPa at t ≤ 16 mm; 345 MPa at 16 < t ≤ 40 mm; 335 MPa at 40 < t ≤ 65 mm | 355 MPa at t ≤ 16 mm; 345 MPa at 16 < t ≤ 40 mm | The nominal 355 MPa value does not apply to every wall thickness |
| Tensile strength, Rm | 470–630 MPa at t ≤ 65 mm | 470–630 MPa at t ≤ 40 mm | Defines the specified resistance range in a tensile test |
| Minimum elongation, A | 22% longitudinal; 20% transverse at t ≤ 65 mm | 22% at t ≤ 40 mm, subject to specimen and section-geometry provisions | Indicates ductility under the stated test conditions |
For EN 10219 sections with D/t < 15, or (B + H)/(2t) < 12.5 for square and rectangular sections, minimum elongation falls by two percentage points. Structural resistance still depends on geometry, tolerances, buckling and connection design.
What Are the S355NH Charpy Impact Requirements?
S355NH requires a minimum average Charpy V-notch absorbed energy of 40 J at −20 °C for three full-size specimens. One result may be below 40 J, provided it is not below 28 J.
| Standard | Test Piece Size | Test Direction | Test Temperature | Minimum Average Absorbed Energy | Minimum Permitted Individual Value |
| EN 10210-1 | 10 × 10 × 55 mm | Longitudinal or transverse, at the manufacturer’s discretion | −20 °C | 40 J | 28 J |
| EN 10219-1 | 10 × 10 × 55 mm | Longitudinal or transverse, at the manufacturer’s discretion | −20 °C | 40 J | 28 J |
The 2006 product standards cite EN 10045-1. ISO 148-1:2016 is the current published ISO method, but changing the referenced method requires contractual agreement.
Test Temperature and Impact Energy Acceptance Criteria
The initial set follows the limits in the table. If it fails, the manufacturer may test three further specimens from the same sample. The six results must average at least 40 J, with no more than two below 40 J and no more than one below 28 J.
The −20 °C test condition does not by itself establish service suitability. Brittle-fracture assessment must also consider design temperature, thickness, stress, loading rate and detail type.
Standard and Reduced-Section Charpy Test Pieces
A full-size specimen measures 10 × 10 × 55 mm. If the wall cannot provide a 10 mm width, a reduced width of at least 5 mm is permitted and the energy requirement falls proportionally.
A 7.5 mm specimen requires a 30 J average and 21 J individual minimum; a 5 mm specimen requires 20 J and 14 J. These editions do not require impact testing below 6 mm. If a 5 mm specimen cannot be taken, ferritic grain size is verified under the applicable provisions.
Test Direction and Sample Location
The manufacturer may select longitudinal or transverse specimens unless the order specifies an orientation.
Circular-section specimens are taken away from the weld where present. Square and rectangular specimens come from midway between corners and, for welded products, a side without the weld. EN 10210-1 Option 1.9 permits specified longitudinal corner-region specimens.
Above 12 mm thickness, one specimen side must be no more than 2 mm from a rolled surface. Curvature may limit specimen width in circular or elliptical sections.
What Is the Chemical Composition of S355NH?
The following cast-analysis limits apply. Nitrogen and carbon-equivalent requirements differ by standard.
| Standard | Element | Maximum or Required Content | Technical Relevance |
| Both standards | Carbon, C | 0.20% max. | Influences hardenability and welding assessment |
| Both standards | Silicon, Si | 0.50% max. | Used for deoxidation and may contribute to strength |
| Both standards | Manganese, Mn | 0.90–1.65% | Contributes to strength and affects CEV |
| Both standards | Phosphorus/sulfur, P/S | 0.035%/0.030% max. | Restricted because excessive content can impair toughness and ductility |
| Both standards | Niobium/vanadium, Nb/V | 0.050%/0.12% max. | May support grain refinement and strength |
| Both standards | Total aluminium/titanium, Al/Ti | 0.020% min./0.03% max. | Nitrogen binding and fine-grain control |
| Both standards | Chromium/nickel/molybdenum/copper | 0.30%/0.50%/0.10%/0.35% max. | Included in hardenability and CEV assessment |
| EN 10210-1 | Nitrogen, N | 0.020% max. | Limit for normalized finished sections |
| EN 10219-1 | Nitrogen, N | 0.015% max. | Limit for N-condition feedstock |
| EN 10210-1 | CEV | 0.43% at t ≤ 16 mm; 0.45% at 16 < t ≤ 65 mm | Thickness-dependent input to welding assessment |
| EN 10219-1 | CEV | 0.43% at t ≤ 40 mm | Input to welding assessment for cold-formed sections |
The aluminium minimum does not apply when sufficient nitrogen-binding elements are present. If copper exceeds 0.30%, nickel must be at least half the copper content. Ordered product analysis uses separate tolerances.
Carbon equivalent is calculated as:
CEV = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15
Preheat also depends on thickness, heat input, diffusible hydrogen, restraint and material temperature.
How Does S355NH Compare with S355J2H and S355NLH?
S355NH specifies more impact energy than S355J2H at −20 °C, while S355NLH is tested at −50 °C. They are not directly interchangeable.
| Grade | Steel Classification | Delivery Condition | Test Temperature | Minimum Average Impact Energy | Main Selection Consideration |
| S355J2H | Non-alloy quality structural steel | EN 10210: hot finished; EN 10219: cold formed welded | −20 °C | 27 J | J2 toughness without N-grade requirements |
| S355NH | Fine-grain non-alloy quality steel | EN 10210: normalized, including normalized rolled; EN 10219: N-condition feedstock with a cold-formed finished section | −20 °C | 40 J | Higher specified energy at −20 °C |
| S355NLH | Fine-grain non-alloy quality steel | EN 10210: normalized, including normalized rolled; EN 10219: N-condition feedstock with a cold-formed finished section | −50 °C | 27 J | Lower test temperature |
All three grades specify 355 MPa minimum yield strength up to 16 mm, but differ in chemistry, delivery condition and toughness.
When Should S355NH Be Specified?
Specify S355NH where an EN-based design requires fine-grain hollow sections with 355 MPa-class yield strength and 40 J impact performance at −20 °C. Confirm the route, thickness, fabrication and inspection plan.
| Project Condition | Why S355NH May Be Considered | Limitation or Additional Check |
| Moderate low-temperature exposure | Provides a 40 J average at −20 °C | Check design temperature, wall thickness, stress level and fracture consequence |
| Hot-finished or normalized sections | Available under EN 10210-1 | Confirm seamless or welded route, size and wall thickness |
| Cold-formed welded sections | Available under EN 10219-1 | Account for cold-forming effects and finished-section properties |
| Extensive welding | Specified chemistry and CEV limits support procedure development | Review actual material certificate, joint restraint, hydrogen control and heat input |
| Service below −20 °C | May be considered only with project-specific assessment or additional testing | Evaluate S355NLH or specified lower-temperature Charpy criteria |
| Structures requiring enhanced notch toughness at −20 °C | Specifies a 40 J average Charpy value at the stated test temperature | Complete the project-specific brittle-fracture assessment |
| Fatigue-sensitive structures | May meet the required static-strength and toughness criteria | Charpy energy does not define fatigue resistance; assess stress range, detail category and weld quality under the governing design standard |
| Fixed offshore structures | Its strength class may be relevant during preliminary material comparison | Check EN 10225-3 and the project specification; separate base-metal, weld and heat-affected-zone requirements may apply |
| Proposed grade substitution | Provides a defined basis for comparison | Obtain design approval and review welding and inspection requirements |
An order should state the standard and edition, grade, shape, dimensions, wall thickness, length, route, surface treatment, quantity and inspection document. For SHS or RHS enquiries, buyers can use the listed square and rectangular hollow section formats as a dimensional reference, then specify EN 10210-1 or EN 10219-1 and S355NH explicitly. Agree any additional Charpy or third-party inspection requirements before production.
Buyers can contact BAOLAI with drawings, specifications, dimensions, quantity, testing and documentation requirements to check manufacturing feasibility and quotation conditions.
Frequently Asked Questions
Does S355NH Require Preheating Before Welding?
Not necessarily. Preheat depends on actual CEV, thickness, heat input, diffusible hydrogen, restraint and material temperature. Controls should follow the applicable welding recommendations and qualified procedure, such as EN 1011-2 and EN ISO 15614-1 where applicable.
Can S355NH Be Welded to S275 Steel?
Generally, yes, using a qualified procedure. Joint design, consumables and welding parameters must reflect both materials. Confirm the exact S275 designation because its suffix and product standard affect delivery and impact requirements.
Is S355NH the Same Under EN 10210 and EN 10219?
No. EN 10210-1 supplies a normalized finished section; EN 10219-1 supplies a cold-formed welded section made from N-condition feedstock. They also differ in thickness coverage, nitrogen limits and dimensions, so the order must identify the product standard.
Can S355NH Replace Another Structural Steel Grade Without Design Approval?
No. The engineer must compare the product standard, route, dimensions, section properties, toughness, weldability and inspection requirements. Approval also depends on the governing design and execution specifications.
When Can a Project Require Tougher Charpy Criteria Than the S355NH Grade Minimum?
Lower design temperatures, thicker walls, high stress, dynamic loading or severe fracture consequences may justify tougher criteria. These can include lower test temperatures, higher energy, fixed orientation, corner sampling, or separate weld and heat-affected-zone tests.
