P355QL1 is a kind of high-strength quenched and tempered fine-grained pressure vessel and boiler steel plate that complies with the European standard EN 10028 - 6. Each part of its grade has a specific meaning: "P" stands for plate, "355" indicates that its minimum yield strength is no less than 355 MPa, "Q" represents the delivery status of quenching and tempering, and "L1" denotes its low-temperature impact toughness grade, which can maintain excellent performance at -50°C.
Chemical Element
| Element | Min | Max | Similar |
|---|---|---|---|
| Cu | - | 0.3000 | - |
| B | - | 0.0050 | - |
| Ti | - | 0.0300 | - |
| Nb | - | 0.0500 | - |
| V | - | 0.0600 | - |
| Mo | - | 0.2500 | - |
| Ni | - | 0.5000 | - |
| Cr | - | 0.3000 | - |
| P | - | 0.0200 | - |
| S | - | 0.0100 | - |
| Mn | - | 1.5000 | - |
| Si | - | 0.4000 | - |
| C | - | 0.1600 | - |
Mechanical Properties
| Yield Rp0.2 (MPa) |
Tensile Rm (MPa) |
Impact KV/Ku (J) |
Elongation A (%) |
Reduction in cross section on fracture Z (%) |
As-Heat-Treated Condition | Brinell hardness (HBW) |
|---|---|---|---|---|---|---|
| 373 (≥) | 762 (≥) | 31 | 42 | 22 | Solution and Aging, Annealing, Ausaging, Q+T,etc | 421 |
Physical Properties
| Temperature (°C) |
Modulus of elasticity (GPa) |
Mean coefficient of thermal expansion 10-6/(°C) between 20(°C) and | Thermal conductivity (W/m·°C) |
Specific thermal capacity (J/kg·°C) |
Specific electrical resistivity (Ω mm²/m) |
Density (kg/dm³) |
Poisson's coefficient, ν |
|---|---|---|---|---|---|---|---|
| 12 | - | - | 0.13 | - | |||
| 712 | 126 | - | 11.3 | 432 | - | ||
| 352 | - | 21 | 24.2 | 242 | 143 |
Processing Characteristics of P355QL1
Mature Quenching and Tempering Process: Adopts the core quenching and tempering process of "quenching + high-temperature tempering". The quenching temperature is controlled at 880-950℃, and the tempering temperature at 550-680℃. Through precise temperature control and holding time adjustment, the grain structure is refined, ensuring the steel obtains uniform strength-toughness matching. The yield strength stably reaches above 355MPa, while ensuring the -50℃ low-temperature impact toughness meets the standard.
Strong Compatibility in Forming Processing: The hot forming temperature is suitable for 1100-1200℃. Within this range, the steel has excellent plasticity and can realize various forming operations such as bending, stamping, and rolling. Air cooling after forming can retain the core mechanical properties without additional heat treatment remediation, which is suitable for the processing of complex components such as large pressure vessels and pipelines.
Easy-to-Control Welding Process: Preheating at 80-150℃ is required before welding according to the plate thickness (when ＞25mm). Common methods such as shielded metal arc welding and gas metal arc welding can be adopted. The grain growth in the heat-affected zone is controllable during welding. Post-weld stress relief heat treatment (if necessary) can reduce residual stress, avoid cold cracking, and the performance of the weld joint has high matching degree with the base material.
Excellent Machinability: Due to its fine grains and uniform hardness (HB200-250), the tool wear during cutting is small. Turning, milling, drilling and other processing can be completed with conventional cutting parameters without special tools or complex process adjustments. The processing efficiency is high, and the surface roughness of the workpiece is easy to meet the standard.
Good Adaptability of Surface Treatment Process: The steel surface is easy to carry out shot blasting derusting and phosphating treatment, and the adhesion of primer and topcoat is strong. Anti-corrosion coating processes can be matched according to application scenarios (such as oil and gas, chemical environments). After treatment, the corrosion resistance is significantly improved, extending the service life of components.
High Controllability in Production Process: In the smelting stage, low phosphorus (≤0.025%) and low sulfur (≤0.010%) control are adopted, combined with microalloying elements such as niobium and vanadium to refine grains. The rolling process adopts controlled rolling and controlled cooling technology to ensure uniform performance in the thickness direction of the steel, no internal defects, and strong batch stability.
applications
Pressure Vessels and Boilers: P355QL1 is extensively used in the fabrication of pressure vessels and boilers operating under severe conditions. Its ability to maintain toughness at temperatures as low as -50°C makes it suitable for equipment handling liquefied gases, refrigerants, and other substances that demand high reliability in cold environments.
Oil and Gas Industry: The material is commonly employed in the construction of storage tanks, separators, heat exchangers, and pipeline components for onshore and offshore oil and gas projects. Its combination of high yield strength and good impact resistance ensures structural integrity even in harsh offshore climates.
Chemical Processing Equipment: Due to its low carbon content and controlled impurities, P355QL1 is ideal for reactors, columns, and other chemical processing equipment that require resistance to stress corrosion and stable performance under varying temperatures and pressures.
Power Generation Systems: It is used in the manufacturing of components for thermal power plants, including boiler drums, headers, and pressure parts, where high-temperature strength and fatigue resistance are essential.
Cryogenic Equipment: P355QL1's low-temperature toughness (L1 grade) makes it a preferred choice for cryogenic storage tanks and transportation systems handling liquefied natural gas (LNG) and other cryogenic fluids.
Heavy Engineering and Structural Components: The steel is also utilized in heavy machinery, large-diameter pipes, and structural parts that require high strength and toughness, particularly in cold regions.
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What is the maximum operating temperature for P355QL1?
P355QL1 can operate at temperatures up to approximately 400°C, depending on the application and design standards. Its elevated-temperature properties are specified in EN 10028-3, ensuring that it maintains sufficient strength and creep resistance for use in boilers and heat exchangers.
How is P355QL1 inspected after fabrication?
After fabrication, P355QL1 components are inspected using methods such as ultrasonic testing, radiography, and magnetic particle inspection. These checks ensure that welds and material structure are free from defects. Visual inspection and dimensional checks are also performed to meet quality standards.
What are the advantages of using P355QL1 in pressure vessels?
P355QL1 offers high strength, good toughness, and excellent weldability, making it ideal for pressure vessels. Its low-temperature performance ensures safety in cold environments, while its fine-grained structure provides consistent mechanical properties. It also allows for lighter designs compared to standard carbon steel.
Can P355QL1 be heat treated?
P355QL1 is typically supplied in the normalized or normalized and tempered condition, which optimizes its strength and toughness. Further heat treatment is not usually required, but stress relief annealing may be applied to reduce welding stresses in thick sections or critical applications.
What is the fatigue resistance of P355QL1?
P355QL1 has good fatigue resistance due to its fine-grained microstructure and controlled impurities. It can withstand cyclic loading in applications such as pressure vessels and pipelines, but design must consider stress concentrations and weld quality to ensure long-term durability under repeated stress.
What is the Charpy impact value of P355QL1?
P355QL1 requires a minimum Charpy V-notch impact energy of 27 J at -20°C, as specified in EN 10028-3. This value ensures that the material remains tough and resistant to brittle fracture in low-temperature conditions, which is critical for safety in pressure-containing equipment.
How does P355QL1 compare to ASTM A516 Grade 70?
P355QL1 and ASTM A516 Grade 70 are both pressure vessel steels, but P355QL1 offers higher strength and better low-temperature toughness. It is also microalloyed, providing improved weldability and more consistent mechanical properties. A516 Grade 70 is more commonly used in North America.
What are the storage requirements for P355QL1 plates?
P355QL1 plates should be stored in a dry, covered area to prevent moisture and corrosion. They should be elevated off the ground and protected from contaminants. Proper labeling and documentation ensure traceability, which is essential for compliance with industry standards and quality control.
What is the typical delivery condition of P355QL1?
P355QL1 is usually delivered in the normalized or normalized and tempered condition, which refines its microstructure and optimizes strength and toughness. The delivery condition is specified by the manufacturer and must comply with EN 10028-3 to ensure consistent performance in critical applications.
Why is P355QL1 preferred for offshore applications?
P355QL1 is preferred for offshore applications due to its high strength, good toughness, and resistance to low temperatures. It can withstand harsh marine environments and cyclic loading, making it suitable for platforms, pipelines, and storage tanks. Its weldability also simplifies fabrication in remote locations.