P355NH is a non-alloy pressure vessel steel grade specified in EN 10028-2. It has good high-temperature strength and toughness, suitable for manufacturing pressure vessels and boilers operating at moderate temperatures. It is widely used in petrochemical, power generation industries.
Mechanical Properties
| Grade | Type | Thickness (mm) | Yield Strength MPa (min) |
Tensile Strength MPa |
Elongation % (min) |
|---|---|---|---|---|---|
| P355 NH | Normalized | ≤ 16 | 355 | 490 - 630 | 21 |
Chemical Composition
| P355 NH | |
|---|---|
| C | 0.18 |
| Si | 0.50 |
| Mn | 1.10 to 1.70 |
| P | 0.025 |
| S | 0.015 |
| Al | 0.020 |
| N | 0.012 |
| Cr | 0.30 |
| Cu | 0.30 |
| Mo | 0.08 |
| Nb | 0.05 |
| Ni | 0.50 |
| Ti | 0.03 |
| V | 0.05 |
P355NH Processing Characteristics
Excellent hot workability：The steel grade features a stable austenite structure in the hot working temperature range of 850–1150℃, with low deformation resistance and uniform plastic flow. It can be smoothly subjected to forging, rolling, bending and other hot forming processes, and the formed workpieces have no obvious internal stress or structural defects, ensuring consistent dimensional accuracy and shape stability of pressure vessel components.
Reliable cold forming performance：With high low-temperature toughness and moderate yield strength, it allows cold bending, stamping and flanging operations without preheating under most forming requirements. For thick plates or complex forming processes, low-temperature preheating (100–200℃) can effectively avoid cold cracking, and the formed parts retain good mechanical properties without secondary heat treatment.
Easy weldability：It is a weldable fine-grained structural steel with low carbon equivalent and controlled impurity content (S, P). It can be welded by common methods such as SMAW, GMAW and SAW without pre-weld heat treatment for thin and medium plates; post-weld stress relief annealing (550–650℃) is only required for thick-walled pressure-bearing structures, ensuring weld joints with high strength, toughness and no cold/hot cracking.
Stable heat treatment response：Normalizing (880–920℃, air cooling) is the main heat treatment process, which refines the ferrite-pearlite structure, optimizes strength and toughness matching, and ensures uniform mechanical properties across the entire steel plate section. The heat treatment process is easy to control, with low sensitivity to cooling rate, suitable for mass production of large and medium-sized pressure vessel parts.
applications
1. Pressure Vessels and Storage Tanks
This is the core application for P355NH, leveraging its excellent resistance to brittle fracture:
Liquefied Gas Tanks: Used for storing LPG (Liquefied Petroleum Gas), butane, and propane.
Chemical Reactors: Utilized in chemical and petrochemical plants for vessels that must withstand constant internal pressure during chemical processing.
Separators & Compressors: Employed in the manufacturing of gas separation units and the outer shells of large-scale industrial compressors.
2. Boilers and Thermal Engineering
Because P355NH maintains its mechanical properties at temperatures up to 400 °C, it is essential for heat-intensive systems:
Boiler Components: Manufacturing of boiler drums, headers, and pressure-bearing pipe fittings.
Heat Exchangers: Used for the shells and internal components of heat exchangers in the power generation and oil refining sectors.
3. Oil, Gas, and Piping Systems
Medium-Pressure Gas Pipelines: Research in 2026 indicates that P355NH is increasingly used in modern gas distribution networks. Its high tensile strength (up to 630-650 MPa) and elongation (>21%) help prevent catastrophic pipe failures during soil shifts or ground movement.
Industrial Pressure Piping: Used for the transport of high-temperature liquids or pressurized gases within industrial complexes.
4. Power and Infrastructure
Energy Sector: Used in steam turbine components and auxiliary pressure-bearing equipment in power plants.
Structural Applications: Occasionally used in bridge components or offshore platforms where a combination of high load-bearing capacity and weldability is required.
5. Specialized Variations
While P355NH is the standard "High-Temperature" (NH) grade, it is part of a family of steels used for different environmental conditions:
P355NH+: Current 2026 industry data shows a trend toward "Plus" versions with micro-alloying (e.g., small additions of Copper) to enhance atmospheric corrosion resistance for outdoor vessels.
P355NL1 & NL2: If the application requires service in sub-zero temperatures (low-temperature toughness), the NL1 or NL2 grades are preferred over the NH grade.
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What is the maximum thickness of P355NH plates?
The maximum thickness of P355NH plates specified in EN 10028-2 is usually 200 mm, but it can be customized according to specific requirements. Thicker plates may need stricter heat treatment and testing to ensure uniform performance through the thickness.
What is the density of P355NH?
The density of P355NH is approximately 7.85 g/cm³, the same as most carbon and low-alloy steels. This value is used for weight calculation in engineering design, material procurement and structural analysis of pressure vessels and other components.
Does P355NH have corrosion resistance?
P355NH has basic corrosion resistance in atmospheric and mild corrosive environments. However, in harsh environments (e.g., acidic, alkaline or saltwater), it needs additional protection like painting, galvanizing or coating to prevent corrosion and extend service life.
What is the tensile strength range of P355NH?
The tensile strength of P355NH ranges from 470 MPa to 630 MPa, as specified in EN 10028-2. This strength level ensures it can withstand high pressure and load in pressure vessel and boiler applications without deformation or failure.
What is the yield strength of P355NH?
P355NH has a minimum yield strength of 355 MPa at room temperature. This means it can resist permanent deformation when subjected to a stress below 355 MPa, which is crucial for maintaining the structural integrity of pressure-bearing components.
Can P355NH be used at low temperatures?
Yes, P355NH can be used at low temperatures down to -20℃. Its minimum impact energy of 30 J at -20℃ ensures it has good toughness and avoids brittle fracture in low-temperature pressure-bearing scenarios, such as cold regions or low-temperature media storage.
What testing methods are used for P355NH?
Common testing methods for P355NH include chemical composition analysis (spectrometry), mechanical tests (tensile, yield, elongation), impact test (Charpy V-notch) at -20℃, and non-destructive testing (ultrasonic, radiographic) to check for internal defects.
What is the elongation requirement of P355NH?
P355NH requires a minimum elongation of 21% in the tensile test. Good elongation ensures the material has sufficient ductility, allowing it to deform plastically before fracture, which is important for absorbing energy during impact or pressure fluctuations.
Is P355NH a low-alloy steel?
P355NH is classified as a non-alloy steel according to EN 10028-2, though it contains trace alloying elements. These trace elements (Cr, Ni, Mo) are added to improve toughness and strength, but their content is below the threshold for low-alloy steels.
What is the hardness of P355NH?
The Brinell hardness (HB) of normalized P355NH is typically between 137 and 179 HB. Hardness testing is used to indirectly assess its strength and microstructure uniformity, ensuring it meets the required mechanical properties for pressure-bearing applications.