P355Q Steel Plate for Pressure Vessel and Boiler

What is P355Q?

P355Q is a fine-grained, weldable, quenched and tempered (Q&T) pressure vessel steel plate conforming to European standard EN 10028-6:2017. The core of its manufacturing process is the quenching and tempering (Q+T) heat treatment, engineered to achieve an optimal combination of high tensile strength and superior low-temperature impact toughness.

Where P355Q Plate Is Used?

• Boiler drums and steam collectors - thick-walled pressure parts where the QT structure earns its keep through a combination of high allowable stress and resistance to brittle fracture during start-up and shut-down cycles.
• Chemical and petrochemical reactors and columns - vessels subject to both pressure and process temperature swings, typically fabricated to EN 13445.
• Storage tanks and spheres - for oil, gas, LPG and chemical media where the minimum design metal temperature stays within the grade's −20 °C toughness limit.
• Heat-exchanger shells and separators - cylindrical pressure parts where the plate is rolled, welded and often post-weld heat treated.

Selection Suggestion:

• European code project, design temp down to −20 °C, want thinner walls → P355Q.
• European code project, conventional design, normalized plate is acceptable → P355NH may be the economic choice.
• ASME project → the designer will normally call an SA grade such as SA537 Cl.2 rather than an EN grade; EN plate can only be used if the code case or the purchaser permits it.
• Design temp below −20 °C → step up within the same family to P355QL1 (−40 °C) or P355QL2 (−60 °C).

Substituting any of these for another across code systems requires written approval from the design engineer; the table is a selection guide, not an equivalence certificate.

P355Q Fabrication and Welding Guidelines

Because the material is delivered in the quenched and tempered (Q&T) condition, proper handling practices must be followed during fabrication to preserve its mechanical properties.

1. Cutting

• Plasma cutting or laser cutting is recommended.
• If oxy-fuel cutting is utilized, preheating to 80–100°C is recommended for heavy gauge plates (e.g., thickness > 30 mm).

2. Cold Forming

• The steel exhibits good cold formability. Bending radii should adhere to standard design recommendations.

3. Welding

• Preheating: Generally required. Preheating temperature should be maintained at approximately 80–120°C, depending on plate thickness and joint restraint. Interpass temperature should be strictly controlled below 200°C.
• Filler Metal Selection: Specify low-hydrogen welding consumables matched to the strength of the base metal.

Covered Electrodes (SMAW): Electrodes complying with EN ISO 2560-A: E 42 4 B 4 2 H5 or EN ISO 18275-A: E 38 4 B 4 2 H5.

Solid Wires / Fluxes (GMAW / SAW): Wires conforming to EN ISO 14171-A: S 42 3 M21 4 H5 or EN ISO 26304-A: G 42 5 M21 4Mo H5, paired with suitable fluxes.

• Heat Input Control: Moderate heat input is recommended to avoid excessive heat input, which can cause softening in the Heat-Affected Zone (HAZ).
• Post-Weld Heat Treatment (PWHT): Stress-relief annealing at 550–580°C is recommended for heavy plate thicknesses or highly restrained joint configurations.

Why Choose us?

1. Flexible size customization: Cut-to-length, slitting, plasma flame cutting, CNC bending and rolling processing per client drawing requirements
2. Our exclusive export standard packaging includes: waterproof film + moisture-proof paper + solid wood pallet + corner protectors.
3. Small free samples can be provided for composition/mechanical testing; 12-month warranty, replacement and refund for non-human-caused quality issues.

FAQ

What is the lowest design temperature for P355Q plate?

The standard guarantees 27 J Charpy at −20 °C. Practical design temperatures usually stop around −20 °C; below that, designers move to P355QL1 (−40 °C) or P355QL2 (−60 °C).

Does P355Q need post-weld heat treatment (PWHT)?

PWHT is a design and code decision, not an automatic requirement. Where code rules or the project spec call for it, typical practice is in the 580–620 °C range - always per the approved WPS and below the tempering temperature, since excessive PWHT can lower the plate's strength. See our P355Q buying and quality guide for more on welding.

Why is P355Q more expensive than P355NH?

The QT heat treatment and the cleaner steel required for reliable quenching add process cost. You pay for the higher strength in thicker sections and the guaranteed −20 °C toughness - decide by design need, not by price per tonne alone.