Does P355NH require post-weld heat treatment ?

P355NH is a high-quality non-alloy pressure vessel steel grade that fully complies with the European standard EN 10028-2, which sets strict technical specifications for steels used in pressure-bearing equipment. Boasting excellent high-temperature strength and superior toughness even under fluctuating temperature conditions, this steel grade is well-suited for manufacturing a wide range of pressure vessels, boilers, and related pressure-bearing components that operate stably under moderate temperature (typically -20℃ to 400℃) and high-pressure working environments. Due to its reliable mechanical properties and good processability, it is widely applied in key industries such as petrochemical, thermal power generation, and chemical engineering, playing a crucial role in equipment for oil refining, gas processing, and steam production systems.

Equivalent Grades of EN 10028-3 P355NH (1.0565) Steel Plate:

P355NH Boiler Plate Steel Chemical Composition:

P355NH Boiler Steel Plate Mechanical Property:

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.

P355NH Applications

Serves as a core material for petrochemical and chemical pressure-bearing equipment, including reactors for crude oil cracking and chemical synthesis, heat exchangers for medium heat transfer, high-pressure spherical tanks for gas and liquid storage, and separators for material purification, adapting to high-pressure and alternating temperature working conditions in production.

Applied to key power generation equipment across thermal, nuclear and hydropower sectors, such as boiler drums, nuclear reactor pressure shells, hydropower high-pressure water pipes and turbine volutes, maintaining stable mechanical properties at high temperatures to ensure safe and continuous operation of power units.

Used in new energy storage and marine engineering components, including high-pressure hydrogen storage and transportation containers, low-temperature adsorbers for air separation equipment, offshore platform structural parts and ship pressure pipelines, with excellent low-temperature toughness to resist marine low-temperature and impact loads.

Fabricates sanitary pressure-bearing equipment for pharmaceutical and food industries, such as raw material storage tanks, closed transportation pipelines and sterile pressure vessels, meeting industry hygiene standards to avoid material pollution during storage and processing.

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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 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 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.

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 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.

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.

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.