P355NH is a normalized, weldable fine-grain structural steel produced according to the European standard EN 10028-3. It is specifically designed for manufacturing pressure vessels, boilers, and pipes that operate in elevated temperature environments, typically up to 400 °C.
Key Specifications
Standard: EN 10028-3 (Steels for pressure purposes).
Material Number: 1.0565.
Designation: "P" stands for Pressure, "355" indicates a minimum yield strength of 355 MPa (for thickness ≤ 16mm), and "NH" signifies it is normalized and intended for high-temperature service.
Delivery Condition: Normalized (heated to 900–950 °C and air-cooled) to achieve a uniform fine-grain structure.
Chemical composition
| Variant | Cast | Weldability | C % | Si % | Mn % | P % | S % | Cr % | Ni % | Mo % | V % | Ti % | Cu % | Al % | Nb % | N % | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 2714 | CC | CEV 0.43max | Min | 0.01 | 0.01 | 1.10 | 0.000 | 0.000 | 0.00 | 0.00 | 0.00 | 0.000 | 0.000 | 0.00 | 0.020 | 0.000 | 0.0000 |
| Pcm 0.27max | Max | 0.18 | 0.50 | 1.70 | 0.025 | 0.010 | 0.30 | 0.50 | 0.08 | 0.100 | 0.030 | 0.30 | - | 0.050 | 0.0120 |
Mechanical Properties
| Variant | Condition | Format | Dimension [mm] | Yield strength min [MPa] | Tensile strength [MPa] | Elongation A5 [%] | Impact (ISO-V) strengthmin |
|---|---|---|---|---|---|---|---|
| Rp0.2 * Reh, ** Rel | |||||||
| 2714 | +AR | Round bar | 25 < 35 | 355* | 490-630 | 22 | -20 °C 40 J (long) |
| Round bar | 35 < 50 | 345* | 490-630 | 22 | -20 °C 40 J (long) | ||
| Round bar | 50 < 70 | 325* | 490-630 | 22 | -20 °C 40 J (long) | ||
| Round bar | 70 < 100 | 315* | 470-610 | 21 | -20 °C 40 J (long) | ||
| Round bar | 100 < 150 | 295* | 450-590 | 21 | -20 °C 40 J (long) | ||
Transformation temperatures
| Temperature °C | |
|---|---|
| MS | 432 |
| AC1 | 717 |
| AC3 | 847 |
P355NH Applications
Petrochemical and chemical industries: It is the core material for manufacturing pressure-bearing equipment like reactors, heat exchangers, separators and spherical tanks, and is widely used in low-temperature storage and transportation devices such as LNG storage tank inner tanks, liquid nitrogen/oxygen tanks, ethylene cracking cold boxes and propylene distillation towers, adapting to the harsh working conditions of deep cooling and high pressure in chemical production.
Power generation industry: Applied to fabricate key components including boiler drums, nuclear reactor pressure shells, high-pressure water pipes of hydropower stations and turbine volutes, maintaining stable mechanical properties at high temperatures up to 400℃ and ensuring the safe operation of power equipment under high-pressure and high-temperature conditions.
Energy storage and marine engineering: Used for hydrogen energy storage and transportation containers, air separation equipment low-temperature adsorbers, offshore platforms and ship structural parts, with excellent low-temperature toughness to resist the low-temperature impact of marine and energy storage environments.
Pharmaceutical and food industries: Adopted to make sanitary pressure vessels, storage tanks and pipelines that meet industry hygiene standards, realizing the safe storage and transportation of pharmaceutical raw materials and food raw materials with its stable material properties and good processability.
processing
1. Heat Treatment & Normalization
P355NH is primarily supplied in a normalized (+N) condition. If it undergoes further processing, the following guidelines apply:
Normalization: Re-normalization is required if hot forming occurs or if cold deformation exceeds 5%. The process involves heating to 900–950 °C, holding for approximately 1 minute per mm of plate thickness after temperature equalization, and cooling in still air.
Stress Relief Annealing: Recommended at 580–620 °C (typically for 90 minutes) to reduce residual stresses after welding, particularly for complex structures or when specified by regulations.
2. Welding Protocols
P355NH is characterized by excellent weldability but requires precision to avoid defects like "sticking" or lack of fusion.
Processes: Manual arc (with basic-coated electrodes), Submerged Arc Welding (SAW), Gas Metal Arc Welding (GMAW), and TIG (often recommended for thin-walled structures) are standard.
Preheating: Generally not required for standard ambient temperatures. However, if the temperature is below +5 °C, preheating to approximately 150 °C is necessary. For thicker sections, preheating between 150–200 °C for one hour is recommended.
Heat Input Control: Critical to maintain toughness. Linear energy should be limited (e.g., ≤25 kJ/cm for joints ≤20mm thick; ≤35 kJ/cm for 20–50mm).
Hydrogen Removal: To prevent cold cracking, a post-weld "hydrogen bake" at 250–300 °C for 2 hours may be applied.
3. Forming and Cutting
Cold/Hot Forming: P355NH offers good properties for both. If hot forming is performed, it must be followed by normalization to restore the fine-grain microstructure.
Cutting: Suitable for all standard thermal cutting methods including laser, plasma, and oxy-propane, as well as waterjet cutting.
Machinability: Generally good, though its low carbon content can lead to "smearing" (built-up edges). High cutting speeds and sharp tools with positive rake angles are recommended to improve chip breaking.
Get an valued quotation for P355NH, Contact GNEE Steel.
What is P355NH?
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.
Which standard defines P355NH?
P355NH is defined by the European standard EN 10028-2, which specifies technical delivery conditions for non-alloy and alloy steels for pressure purposes. This standard regulates its chemical composition, mechanical properties, heat treatment and testing requirements.
What are the main chemical components of P355NH?
The main chemical components of P355NH include C (≤0.20%), Si (≤0.35%), Mn (1.00-1.60%), P (≤0.025%), S (≤0.015%), and trace elements like N, Cu, Cr, Ni, Mo to ensure its performance.
What are the mechanical properties of P355NH?
P355NH has a minimum yield strength of 355 MPa and a minimum tensile strength of 470-630 MPa. It has good impact toughness, with a minimum impact energy of 30 J at -20℃, meeting the requirements of low-temperature pressure-bearing environments.
What is the application temperature range of P355NH?
P355NH is suitable for service temperatures between -20℃ and 400℃. It maintains stable mechanical properties within this range, making it ideal for pressure vessels, boilers and pipelines that work under moderate temperature and pressure conditions.
Is P355NH a weldable steel?
Yes, P355NH has excellent weldability. It can be welded using common methods like arc welding, gas welding and resistance welding. Proper preheating (usually 80-150℃) and post-weld heat treatment are recommended to avoid weld cracks and ensure joint performance.
What heat treatment is required for P355NH?
P355NH is usually supplied in the normalized condition (heating to 890-950℃, holding for a certain time, then air cooling). Normalization improves its microstructure, enhances toughness and ensures uniform mechanical properties across the material.
What is the difference between P355NH and P355N?
The main difference lies in the impact test temperature. P355NH requires impact testing at -20℃, while P355N is tested at 20℃. Both meet the same yield and tensile strength requirements, but P355NH has better low-temperature toughness.
Can P355NH be used in pressure vessels?
Absolutely. P355NH is specially designed for pressure vessel manufacturing. Its high strength, good toughness and resistance to moderate temperatures make it suitable for storing and transporting gases, liquids and other media under pressure in various industries.
What industries commonly use P355NH?
P355NH is widely used in petrochemical, power generation (thermal power plants), chemical, oil and gas, and boiler manufacturing industries. It is used to make pressure vessels, boilers, heat exchangers and pipelines for high-pressure and high-temperature media.