P355NH Pressure Vessel & Boiler Steel Plate

What Is P355NH?

P355NH is a normalized, weldable fine-grain steel for pressure purposes to EN 10028-3:2017 (material number 1.0565), specified for boilers, heat exchangers and pressure vessels where elevated-temperature strength and guaranteed notch toughness from −20 °C upward are required. EN 10028-3 P355NH boiler steel plate is delivered normalized, with a guaranteed minimum yield strength of 355 MPa for plates up to 16 mm thick; the +N fine-grain delivery keeps strength, elevated-temperature properties and the −20 °C impact guarantee reproducible from heat to heat. The sections below cover the chemical composition, mechanical properties, equivalent grades and the sizes we can quote ex-stock.

Every character in the designation carries a defined meaning. P stands for steel for pressure purposes; 355 is the specified minimum yield strength of 355 MPa for plates up to 16 mm thick; N denotes the normalized delivery condition; and H marks the grades for which elevated-temperature properties are specified. Material number 1.0565 is the numeric designation of P355NH under the EN 10028 system; it appears on certificates alongside the grade name.

Cross-standard equivalents are indicative only. Differences in impact-test requirements, delivery condition and code acceptance mean that direct substitution must be re-qualified by the design authority.

Key Advantages of P355NH PVQ Plate

1. 355 MPa minimum yield with specified elevated-temperature properties. P355NH guarantees 355 MPa yield strength for plates up to 16 mm, and the H designation means elevated-temperature proof-strength properties are specified, not assumed. Designers get a defined strength basis at room temperature and in service.
2. Normalized fine-grain microstructure for consistent toughness. Normalizing refines the grain and evens the structure across the plate cross-section. The payback is reproducible Charpy values and predictable through-thickness behaviour in thick sections, which keeps fabrication rework down.
3. Good weldability - CEV ≤ 0.43 for t ≤ 60 mm. The maximum carbon equivalent is 0.43 for plates up to 60 mm thick and 0.45 for plates over 60 mm up to 100 mm. P355NH therefore sits inside the envelope that shop welding procedure specifications accept.
4. Complete documentation: EN 10204 3.1 as standard. Every plate is traceable to its heat and ships with an EN 10204 type 3.1 mill certificate as standard. For projects under PED 2014/68/EU the documentation supports conformity assessment, and type 3.2 certification can be added where the client or design code requires independent witnessing.

Typical Applications of P355NH Boiler Plate

P355NH boiler plate goes into pressure parts that run hot, see pressure cycles and must stay ductile down to −20 °C:

• Boiler shells and steam drums - drum and shell plate for fire-tube and water-tube boilers.
• Superheaters and headers - the H designation's elevated-temperature properties apply here.
• Heat exchangers and condensers - shell plate under cyclic pressure.
• Reactor vessels and autoclaves - chemical process vessels built from thick normalized plate.
• High-pressure piping - plate for pressure piping.
• Pulp-and-paper digesters - large continuous-cooking vessels.

P355NH Plate Welding & Fabrication Notes

P355NH is a normalized fine-grain steel with a controlled carbon equivalent, so it welds predictably with shop-standard processes. The guidance below is general; the binding documents for any weld remain the project welding procedure specification (WPS) and the governing fabrication code.

• Welding processes: SMAW, SAW, GMAW and FCAW are all suitable with filler metal matched to the parent-plate strength level.
• Preheat: specify it in the WPS. Judge the requirement case by case on plate thickness, CEV and heat input rather than from a fixed table.
• Cold forming: as a works-practice guide, use a minimum inside bend radius of about 2 × t; verify the exact figure against the relevant EN specification and project requirements.
• Post-weld treatment: where stress relief or re-normalizing is required after welding, carry it out in line with the steelworks' recommendations for P355NH.

Why Choose GNEE Steel?

GNEE carries P355NH steel plate in the normalized condition across the thickness bands boiler and vessel buyers order, and can arrange additional processing on the same order.

• Quotation within 24 hours of receiving your size list.
• Ex-stock plates in the 6–300 mm range with EN 10204 3.1 certificates.
• Normalizing, UT, cutting and beveling consolidated into one order.
• Export packing and supervised loading for sea freight to the destination port.

The P355 Family: P355N vs P355NH vs P355NL1 vs P355NL2

P355NH is one of four grades in the EN 10028-3 P355 family. All four share the normalized fine-grain route and differ in guaranteed impact temperature and, for the low-temperature grades, in phosphorus and sulphur limits.

P and S limits compiled per the current edition of EN 10028-3; the mill test certificate governs.

Choose P355NH when the vessel operates at elevated temperature and must still meet a −20 °C transverse impact guarantee, as boiler drums, heat-exchanger shells and hot-wall process reactors normally do. Step to P355NL1 for −40 °C LPG and low-temperature duty, or to P355NL2 where the design calls for −50 °C with tighter phosphorus and sulphur limits.

FAQ

What is the difference between P355NH and P355GH?

P355GH is a non-alloy steel for elevated-temperature pressure service, specified in EN 10028-2. P355NH is a normalized fine-grain steel in EN 10028-3 with guaranteed impact toughness from −20 °C upward. In practice the P355NH vs P355GH decision turns on the impact-test requirement and the material tables of the governing code; the two grades are not interchangeable.

In which condition is P355NH supplied?

Normalized, written as +N - the delivery condition EN 10028-3 prescribes for this grade, confirmed on the mill test certificate for every plate.

What is the ASME/ASTM equivalent of P355NH?

SA516 Gr.70 is the closest approximation commonly quoted. It remains an approximation: impact-test requirements, delivery condition and code acceptance differ between the ASME/ASTM and EN 10028-3 systems, so any substitution must be re-qualified by the design authority.

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