P355M steel (also known by the material number 1.8821) is a European standard (EN 10028-5) weldable, fine-grained structural steel designed for pressure vessels and boilers, delivered in a thermo-mechanically rolled condition. The "P" signifies its use in pressure vessels, the "355" indicates a minimum yield strength of 355 MPa, and "M" denotes the thermo-mechanical rolling heat treatment and impact testing at -20°C.
| Grade : | P355M | |
| Number: | 1.8821 | |
| Classification: | Alloy special basic steel | |
| Standard: |
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| Equivalent grades: | No information |
Chemical composition
| C | Si | Mn | Ni | P | S | Mo | V | N | Nb | Ti | Al | - |
| max 0.14 | max 0.5 | max 1.6 | max 0.5 | max 0.025 | max 0.01 | max 0.2 | max 0.1 | max 0.015 | max 0.05 | max 0.05 | max 0.02 | Cr+Cu+Mo < 0.6, V+Nb+Ti < 0.15 |
Mechanical properties
| Rm - Tensile strength (MPa) | 450-610 |
| Nominal thickness (mm): | to 40 | 40 - 63 |
| ReH - Minimum yield strength (MPa) | 355 | 345 |
| KV - Impact energy (J) transverse, | -20° 27 |
0° 40 |
+20° 60 |
| A - Min. elongation at fracture (%) | 22 |
applications
Pressure vessels and storage tanks for the oil and gas industry
Boilers and heat exchangers in power plants and industrial facilities
Large-diameter pipes and pipeline components
Heavy machinery and structural parts requiring high strength and toughness
Offshore structures and components exposed to harsh environmental conditions
Thick-walled fabrications where good weldability and formability are essential
P355M Steel: Processing
Thermomechanical rolling (TMR): As the core production process, P355M undergoes controlled heating to 1050-1150℃, followed by hot rolling with precise deformation control. The rolling process is matched with accelerated cooling (ACC) to refine grain size, forming a uniform fine-grained microstructure. This process eliminates the need for subsequent normalization, reducing production cycles and costs while ensuring high strength and toughness.
Welding processing: Compatible with common welding methods including SMAW (shielded metal arc welding), GMAW (gas metal arc welding), SAW (submerged arc welding), and FCAW (flux-cored arc welding). Preheating to 50-100℃ is usually required to prevent cold cracking, and post-weld heat treatment (PWHT) is not necessary for most applications, which simplifies on-site and factory fabrication.
Forming processing: Possesses good cold and hot formability. Hot forming can be conducted at 800-900℃ to reduce forming resistance, suitable for bending, stamping, and forging complex components. Cold forming is feasible for thin to medium thickness plates, with appropriate ductility to avoid cracking during shaping operations.
Machining processing: Exhibits satisfactory machinability. It can be processed by turning, milling, drilling, and grinding with standard cutting tools. Proper cutting parameters (moderate cutting speed, feed rate, and depth of cut) are recommended to reduce tool wear and ensure processing accuracy, meeting the dimensional requirements of precision components.
Surface treatment: For corrosion protection, common surface treatments include shot blasting, pickling, coating, and galvanizing. Shot blasting removes surface oxides and impurities to improve coating adhesion, while pickling eliminates rust and scale. Coating or galvanizing is applied in harsh environments to enhance corrosion resistance and extend service life.
Equivalent Grades
P355M belongs to a family of EN 10028 standards for flat steel products for pressure purposes. Other related grades include:
P355ML1 and P355ML2: These grades are also thermo-mechanically rolled, but designed for even lower temperature applications, with impact testing at -40°C and -50°C respectively.
P355GH: A normalized steel grade used for high-temperature service up to 400°C.
ASTM A572 Grade 50: Considered a similar grade in the US ASTM standard for structural applications, with comparable mechanical properties.
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What is the density of P355M steel?
The density of P355M steel is approximately 7.85 g/cm³, the same as most carbon and low-alloy steels. This density value is widely used in weight calculation and structural design of steel components.
Can P355M be used in offshore oil and gas platforms?
Yes, P355M is suitable for offshore oil and gas platforms. Its high strength, good weldability, and low-temperature toughness can withstand harsh marine environments and pressure loads, ensuring structural stability and safety.
What is the sulfur content limit in P355M?
The maximum sulfur content in P355M steel is 0.015%. Sulfur forms brittle inclusions, which seriously affect weldability and toughness, so low sulfur content is essential for ensuring the steel's quality.
How to store P355M steel plates to prevent corrosion?
P355M steel plates should be stored in a dry, well-ventilated warehouse, away from moisture and corrosive media. They should be placed on wooden pallets to avoid contact with the ground, and covered with waterproof cloth if stored outdoors.
Can P355M be cold-formed?
P355M can be cold-formed under appropriate conditions. However, cold forming may increase internal stress and reduce toughness, so it is recommended to perform stress relief annealing after cold forming to restore mechanical properties.
What is the difference between P355M and P355ML?
P355ML is a thermomechanically rolled version of P355M. P355ML has finer grain structure, better toughness, and higher strength than P355M, suitable for more demanding low-temperature and high-pressure applications.
Does P355M need to be normalized?
P355M may need normalization (heating to 890-950℃, holding, then air cooling) in some cases, especially for thick plates. Normalization refines grain structure, improves uniformity of mechanical properties, and reduces internal stress.
What is the maximum operating temperature for P355M?
The maximum recommended operating temperature for P355M is around 400℃. Beyond this temperature, its strength and toughness will gradually decrease, which may affect the safety and service life of the components.
Can P355M be used for structural steel beams?
Yes, P355M can be used for structural steel beams, especially in projects requiring high strength and low-temperature resistance (such as cold regions). Its good weldability and ductility facilitate beam fabrication and installation.
What is the hardness of P355M steel?
The Brinell hardness (HB) of P355M steel is usually between 137 and 179. This moderate hardness balances strength and ductility, making it easy to process (cutting, drilling) and weld.