P355NH steel is a normalized, weldable fine-grain steel grade specifically designed for pressure purposes under the European standard EN 10028-3.
The designation itself reveals the material's core identity: "P" stands for pressure purposes, "355" indicates a minimum yield strength of 355 MPa (for thicknesses up to 16 mm), "N" denotes normalized condition, and "H" specifies suitability for elevated-temperature service. The grade is also identified by steel number 1.0565 in the European numbering system.
As a non-alloy quality steel with specified elevated-temperature properties, P355NH steel is engineered to perform reliably in environments where operating temperatures can reach up to 400°C. The normalization heat treatment refines the grain structure, producing a uniform microstructure that enhances both mechanical properties and welding characteristics. This makes P355NH a preferred choice over conventional carbon steels when applications demand a combination of moderate strength, good ductility, and resistance to thermal degradation over prolonged service periods.
GNEE Steel supplies P355NH steel plates in thicknesses ranging from 6 mm to 300 mm, widths from 1,500 mm to 4,050 mm, and lengths from 3,000 mm to 15,000 mm. We also offer customized cutting, edge preparation, and ultrasonic testing (UT) services to meet specific project requirements.
Our P355NH plates are produced in strict accordance with EN 10028-3 standards and come with full EN 10204 3.1 mill test certificates, ensuring complete material traceability from melt to delivery. In this comprehensive guide, we will walk you through every aspect of P355NH steel-from chemical composition and mechanical properties to real-world applications and quality assurance-so you can specify and source with confidence.
Chemical Composition of P355NH Steel (EN 10028-3)
| Element | Content (Max %) |
|---|---|
| Carbon (C) | 0.18 |
| Silicon (Si) | 0.50 |
| Manganese (Mn) | 1.10 – 1.70 |
| Phosphorus (P) | 0.025 |
| Sulfur (S) | 0.015 |
| Chromium (Cr) | 0.30 |
| Nickel (Ni) | 0.50 |
| Molybdenum (Mo) | 0.08 |
| Niobium (Nb) | 0.05 |
| Titanium (Ti) | 0.03 |
| Vanadium (V) | 0.10 |
| Nitrogen (N) | 0.012 |
| Aluminum (Al) | 0.020 (min) |
| Copper (Cu) | 0.30 |
| Nb + Ti + V | ≤ 0.12 |
Mechanical Properties of P355NH Steel – Room Temperature
| Nominal Thickness (mm) | Min. Yield Strength ReH (MPa) | Tensile Strength Rm (MPa) | Min. Elongation A (%) |
|---|---|---|---|
| ≤ 16 | 355 | 490 – 630 | 22 |
| 16 > to ≤ 40 | 345 | 490 – 630 | 22 |
| 40 > to ≤ 60 | 335 | 490 – 630 | 22 |
| 60 > to ≤ 100 | 315 | 470 – 610 | 21 |
| 100 > to ≤ 150 | 305 | 460 – 600 | 21 |
| 150 > to ≤ 250 | 295 | 450 – 590 | 21 |
*Data referenced from EN 10028-3 and verified supplier datasheets*
Impact Energy of P355NH Steel – Transverse (KV, J)
| Test Temperature | Typical Min. Impact Energy (J) |
|---|---|
| -20 °C | 27 – 30 |
| 0 °C | 35 – 40 |
| +20 °C | 39 – 50 |
Elevated Temperature Properties of P355NH Steel
What distinguishes P355NH steel from standard structural steels is its qualification for elevated-temperature service-the "H" in the designation explicitly indicates this capability. According to EN 10028-3, P355NH is designed to maintain its mechanical integrity at operating temperatures up to 400°C, making it suitable for steam boilers, hot water systems, and high-temperature process equipment.
The normalized microstructure plays a pivotal role here. Unlike as-rolled steels that may experience microstructural degradation under sustained thermal exposure, the stable grain structure of normalized P355NH resists creep deformation and maintains yield strength at elevated temperatures.
This is particularly important in applications such as:
- Steam boiler drums and shells operating at temperatures between 200 °C and 350 °C
- Process heat exchangers in petrochemical plants
- Hot liquid storage and transport vessels
- Reactor pressure components in chemical synthesis units
For project engineers and fabricators, this means that P355NH steel can be specified with confidence across a wide operating temperature band without the added cost of higher-alloy grades like P460NH-provided the design stresses and temperatures fall within the grade's validated range.
P355NH vs. P355NL1 and P355NL2 – Understanding the Differences
When reviewing EN 10028-3 grades, it is helpful to understand where P355NH fits relative to its family members.
The key distinction lies in the low-temperature impact testing requirements:
- P355NH: Impact test at -20 °C, optimized for elevated-temperature applications (up to ~400 °C)
- P355NL1: Impact test at -40 °C, suitable for low-temperature pressure vessels and cold-region installations
- P355NL2: Impact test at -50 °C, offering superior ultra-low-temperature toughness for cryogenic-adjacent service
GNEE Steel stocks and supplies all three variants, and our technical team can help you determine which grade best matches your project's operating conditions, design code requirements, and environmental factors.
Processing and Testing Services for P355NH Steel
Beyond supplying standard plate dimensions, GNEE Steel offers value-added processing and testing services that streamline project fabrication:
- Ultrasonic Testing (UT): In-house ultrasonic inspection per EN 10160 or ASTM A578 to verify internal soundness
- HIC / SSC Testing: Hydrogen Induced Cracking and Sulfide Stress Cracking testing per NACE MR0175 for sour service applications
- Through-Thickness Tensile Testing (Z-grade): Z15, Z25, Z35 testing for applications requiring resistance to lamellar tearing
- Fixed-Size Cutting: Precision cutting to your exact dimensions, reducing on-site processing and scrap
- Surface Preparation: Shot blasting to Sa 2.5 and shop priming for corrosion protection during transit and storage
These services reflect GNEE Steel's commitment to being more than a stock supplier-we are a comprehensive partner for pressure vessel steel procurement, capable of delivering fabrication-ready material that reduces your downstream costs and lead times.
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FAQ
What is the maximum operating temperature for P355NH steel?
P355NH steel is designed for elevated-temperature service and is most widely applied in applications operating up to approximately 400 °C. For sustained operations at temperatures approaching or exceeding this range, consulting the relevant design code (e.g., EN 13445) and considering alternative higher-alloy grades is recommended.
Can P355NH steel be used in sour service (H₂S) environments?
P355NH steel is not inherently qualified for sour service; however, supplementary HIC (Hydrogen Induced Cracking) and SSC (Sulfide Stress Cracking) testing per NACE MR0175 can be arranged upon request. GNEE Steel can supply P355NH plates with HIC/SSC testing for applications involving wet H₂S service, subject to order-specific technical review.
What is the difference between P355N, P355NH, and P355NL1?
All three grades have the same minimum yield strength and belong to the EN 10028-3 family, but they differ in temperature qualification: P355N is for general pressure purposes (impact test at -20 °C), P355NH is optimized for elevated-temperature service (up to ~400 °C, impact at -20 °C), and P355NL1 is intended for low-temperature applications (impact test at -40 °C).
Does GNEE Steel supply P355NH pipes and fittings?
GNEE Steel primarily supplies P355NH steel plates in flat product form. For P355NH seamless pipes (EN 10216-3), welded pipes (EN 10217-3), and butt-welding fittings (EN 10253-2), we recommend consulting our pipe division for availability.
Ready to source P355NH steel for your next project? Contact GNEE Steel today. Send us your specifications-grade, dimensions, quantity, and destination-and our team will respond with a competitive quotation within hours. You can reach us via email, phone, or the inquiry form on our website. Let GNEE Steel be your reliable, long-term partner for pressure vessel steel solutions.
