The Specification of P275NH steel plate

Under the EN 10028 standard, P275NH steel plate and sheet are classified as steels for boilers and pressure vessels. P275NH is a normalized, fine-grain pressure vessel steel designed for elevated-temperature service, widely used in the manufacture of pressure vessels, boilers, heat exchangers, and pipes for hot liquids.

Thanks to its controlled chemical composition and stable mechanical properties, P275NH offers a good balance of strength, ductility, weldability, and high-temperature performance, making it suitable for medium-pressure applications.

Standard: EN 10028-2

Steel type: Non-alloy quality steel for pressure purposes

Delivery condition: Normalized (N)

Material number: 1.0487

Typical service temperature: Elevated temperature applications

Main applications: Boilers, pressure vessels, hot liquid pipelines

Technical note: The low carbon content combined with controlled micro-alloying elements ensures excellent weldability and sufficient creep resistance for elevated-temperature service.

Mechanical properties vary with thickness and are guaranteed according to EN 10028 requirements.

*Values marked with (*) indicate transverse test direction results.

Explanation: P275NH steel is not primarily intended for low-temperature service, but it still provides reliable toughness at room and moderately reduced temperatures, ensuring operational safety during pressure fluctuations.

Boilers and Boiler Drums

P275NH steel plates are widely used in the fabrication of industrial boilers and boiler drums, where materials are required to withstand internal pressure and continuous exposure to elevated temperatures.
Thanks to its normalized fine-grain structure and stable mechanical properties, P275NH ensures structural integrity, uniform strength distribution, and reliable long-term performance in boiler shells, headers, and pressure-containing components.

Pressure Vessels and Reactors

P275NH is commonly applied in pressure vessels, reactors, and separators operating under moderate pressure and elevated temperature conditions.
Its controlled chemical composition provides good weldability and resistance to deformation, making it suitable for cylindrical shells, dished ends, and internal structural parts used in chemical processing, petrochemical storage, and energy systems.

Heat Exchangers

In shell-and-tube and plate-type heat exchangers, P275NH steel plates are used for shells, tube sheets, and pressure-bearing components.
The steel's balanced strength and ductility allow it to perform reliably under thermal cycling and pressure fluctuations, ensuring safe heat transfer in power plants, refineries, and industrial heating systems.

Hot Water and Steam Pipelines

P275NH steel is suitable for manufacturing hot water pipelines and steam transport systems, where resistance to thermal stress and internal pressure is essential.
Its normalized condition enhances dimensional stability, reducing the risk of cracking or deformation during long-term operation at elevated temperatures.

Petrochemical and Power Plant Equipment

P275NH steel plates are extensively used in petrochemical facilities and power generation plants, including components such as pressure tanks, heat recovery units, and auxiliary pressure systems.
The material provides a cost-effective solution for equipment that requires consistent mechanical performance, compliance with EN pressure vessel standards, and ease of fabrication.

EN 10028 P275NH steel plate and sheet are normalized pressure vessel steels offering dependable strength, good weldability, and stable performance at elevated temperatures.

With its well-balanced chemical composition and thickness-dependent mechanical properties, P275NH is a cost-effective solution for boiler and pressure vessel fabrication where high-temperature resistance and structural reliability are required.

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1. Q: What is the fundamental difference between P275N, P275NH, P275NL1, and P275NL2?
A: The core distinction lies in their guaranteed impact toughness temperatures and application temperature ranges, which result from differences in chemical composition control and delivery condition requirements.
* P275N: Guarantees impact toughness at room temperature and down to -20°C. Suitable for general pressure vessels and boilers (-20°C to +350°C).
* P275NH: Builds upon P275N with stricter chemical controls (e.g., lower S, P content) to ensure mechanical property stability at elevated temperatures. Suitable for higher temperature service (up to +400°C), such as steam headers and high-temperature vessels.
* P275NL1: Guarantees impact toughness down to -50°C (longitudinal specimens). Designed for low-temperature environments (e.g., -40°C to +350°C).
* P275NL2: Guarantees impact toughness down to -60°C (longitudinal specimens) with even tighter control of S and P. Intended for more severe cryogenic applications (e.g., -50°C to +350°C), such as LNG-related equipment.

2. Q: Why is controlling heat input and performing PWHT particularly important when welding P275NH plate?
A: P275NH is designed for high-temperature service.
* Controlling Heat Input (typically recommended ≤35 kJ/cm): Prevents excessive grain growth in the Heat-
* Mandatory PWHT Requirement: Primarily aims to eliminate welding residual stresses. Under high-temperature and high-pressure conditions, residual stresses can promote stress corrosion cracking or creep damage. PWHT significantly reduces these stresses, enhancing the long-term safety and dimensional stability of the structure at high temperatures.

3. Q: How is the allowable stress for P275N steel plate determined at different design temperatures?
A: The room temperature yield strength cannot be used directly. It is essential to consult the allowable stress values at the design temperature provided in the relevant pressure vessel design codes (e.g., ASME BPVC Section II-D, EN 13445-2). These values are derived from the material's strength properties at elevated temperatures, considering factors like creep and oxidation, and then divided by a safety factor. For example, the allowable stress for P275N at 350°C is significantly lower than its value at room temperature.

4. Q: When purchasing P275NL1/NL2 plate, what is the most critical acceptance test besides room temperature mechanical properties?
A: The most critical test is the Low-Temperature Impact Toughness (Charpy V-notch, CVN). Strict adherence to contract and standard (EN 10028-3) requirements is necessary:
* Verify Test Temperature: Is it -40°C, -50°C, or another specified temperature?
* **Verify SpecVerify Specimen Orientation: Transverse (T) or Longitudinal (L). Standard requirements for longitudinal specimens are typically higher than for transverse. The guaranteed values for NL1 and NL2 primarily apply to longitudinal specimens.
* Verify Acceptance Value: Confirm that the minimum impact energy (J) meets the requirement. This is the key indicator to prevent brittle fracture at low temperatures.

5. Q: What does the "Normalized" condition of P275N steel plate imply, and how does it affect fabrication?
A: "Normalized" is the standard delivery condition. It means the plate is reheated above its austenitizing temperature after rolling and then cooled uniformly in air.
* Purpose: To refine grain structure, homogenize the microstructure, improve mechanical properties and toughness, and relieve internal stresses.
* Impact on Fabrication: Subsequent hot forming (e.g., hot rolling into shells) or welding (equivalent to localized reheating and cooling) alters the material's condition. If the hot working temperature enters the normalizing range and is followed by air cooling, it may have a "normalizing effect." However, excessive temperatures or improper cooling can degrade properties. Therefore, for critical pressure parts subjected to significant hot work, re-normalizing heat treatment may be required to restore the specified properties.

6. Q: The yield strength of P275N plate varies with thickness. How is this considered in design?
A: EN 10028-3 clearly specifies the minimum yield strength (ReH) values for different thickness ranges (e.g., decreasing from 275 MPa for ≤16mm to 235 MPa for >100mm). This reflects the "thickness effect" where thicker sections cool slower, leading to a slight reduction in strength.
* In Design: The corresponding minimum yield strength value for the actual thickness range of the plate being used must be selected for calculations.
* In Procurement and Certification: The manufacturer's test certificate must provide the actual measured yield strength for the batch, corresponding to its thickness. This value must be ≥ the standard's specified minimum for that thickness.

7. Q: Can P275N be used interchangeably with common carbon steels (e.g., Q235B, Q345R) or American standard materials (e.g., SA516 Gr.60)?
A: They are not directly interchangeable. So-called "equivalent" grades are for approximate reference only.
* Different Standard Systems: P275N conforms to the European standard (EN). Its chemical composition, mechanical properties, test methods, and acceptance criteria differ from Chinese (GB) or American (ASTM/ASME) standards.
* Differences in Key Properties: Even if the strength levels are similar, there can be variations in the alloying system, impact toughness requirements, and applicable temperature ranges.
* Correct Procedure: Any material substitution must be re-calculated and approved by the design authority, ensuring the new material fully complies with all requirements of the original design code. Compatibility with the welding procedure must also be re-evaluated.