P355NH steel (1.0565): properties, composition, equivalents
P355NH (1.0565, ex WStE355) is the EN 10028-3 normalized fine-grain pressure-vessel steel: 355 MPa yield, 490–630 MPa tensile, Rp0.2 to 400 °C, 27 J at −20 °C. Data, N/NH/NL1/NL2 family, A516-70/SA-516 equivalents.
What is P355NH?
P355NH is the 355 MPa class of EN 10028-3, the European standard for normalized, weldable fine-grain steels for pressure purposes. Grain refinement with aluminium, niobium and vanadium (Nb + Ti + V ≤ 0.12 %) gives the toughness that plain C-Mn steel cannot reach at this strength: 27 J at −20 °C transverse for the NH and N variants, −40 °C for NL1 and −50 °C for NL2. The H suffix adds a guaranteed yield table up to 400 °C (210 MPa at 400 °C). Werkstoff number 1.0565; the DIN 17102 name WStE355 is still common.
It is the standard plate for LPG spheres and bullets, air receivers, pressure vessels in refineries and chemical plants, and — as P355NL1/NL2 — for ammonia, propane and other refrigerated-gas storage. Because carbon stays ≤ 0.20 % and CEV ≤ 0.43 %, welding is straightforward for a 355 MPa steel.
The ASME counterparts are A516-70 (lower yield, 260 MPa) and A537 Class 1 (345 MPa, normalized) — both 'near'; JIS SPV355 is identical in intent.
P355NH chemical composition
| Element | Mass % | Note |
|---|---|---|
| C | ≤ 0.2 | |
| Si | ≤ 0.5 | |
| Mn | 1.1 – 1.7 | |
| P | ≤ 0.025 | |
| S | ≤ 0.01 | |
| Al | ≥ 0.02 | total; fine-grain treatment |
| N | ≤ 0.02 | |
| Cr | ≤ 0.3 | |
| Cu | ≤ 0.3 | |
| Mo | ≤ 0.08 | |
| Nb | ≤ 0.05 | |
| Ni | ≤ 0.5 | |
| Ti | ≤ 0.03 | |
| V | ≤ 0.1 | Nb + Ti + V ≤ 0.12 |
EN 10028-3:2017 Table 1; Cr + Cu + Mo ≤ 0.45. CEV max 0.43 % (≤ 60 mm), 0.45 % (60–100 mm). P355N (1.0562) same chemistry without elevated-temperature yield; P355NL1 (1.0566): P/S 0.025/0.010, impact −40 °C; P355NL2 (1.1106): Ni ≤ 0.50, impact −50 °C.
P355NH mechanical properties
| Thickness / condition | Yield strength ReH / Rp0.2 MPa (ksi) | Tensile strength Rm MPa (ksi) | Elongation A % | Hardness |
|---|---|---|---|---|
| ≤ 16 mm, +N | 355 (51.5) | 490–630 (71.1–91.4) | 22 | ≈ 150–190 HB (typ.) |
| > 16 ≤ 40 mm | 345 (50.0) | 490–630 (71.1–91.4) | 22 | — |
| > 40 ≤ 60 mm | 335 (48.6) | 490–630 (71.1–91.4) | 22 | — |
| > 60 ≤ 100 mm | 315 (45.7) | 480–620 (69.6–89.9) | 21 | — |
| > 100 ≤ 150 mm | 295 (42.8) | 470–610 (68.2–88.5) | 21 | — |
| Rp0.2 at 100 °C (≤ 60 mm) | 314 (45.5) | — | — | — |
| Rp0.2 at 200 °C | 284 (41.2) | — | — | — |
| Rp0.2 at 300 °C | 250 (36.3) | — | — | — |
| Rp0.2 at 400 °C | 210 (30.5) | — | — | — |
EN 10028-3 Tables 2–4; transverse for plate. Impact (transverse): NH/N ≥ 27 J at −20 °C, ≥ 40 J at 0 °C, ≥ 55 J at +20 °C; NL1 ≥ 27 J at −40 °C; NL2 ≥ 27 J at −50 °C. Longitudinal values are ~15 J higher.
Impact toughness
P355NH requires a minimum Charpy V-notch energy of 27 J at -20 °C (transverse (P355NH / P355N); NL1 −40 °C, NL2 −50 °C). The letter after N shows the toughness class: H = elevated temperature, L1/L2 = low temperature.
P355NH equivalent grades
| Grade | System | Match | Why / differences |
|---|---|---|---|
| IS 2041 R355 | IS (India) | Identical | IS 2041 (pressure-vessel plate) grade R355. |
| SPV355 | JIS (Japan) | Identical | JIS G3115 SPV355: yield 355 MPa, Rm 520–640 MPa; SPV355N (normalized). |
| A516 Gr. 70 | ASTM / ASME | Near | ASTM/ASME A516-70: yield 260 MPa, Rm 485–620 MPa, C ≤ 0.27–0.31 — the common US vessel plate, but lower yield and no micro-alloy fine-grain guarantee. Order normalized with Charpy (S5) for a closer match. |
| A537 Cl. 1 | ASTM / ASME | Near | Normalized C-Mn-Si vessel plate: yield 345 MPa (≤ 65 mm), Rm 485–620 MPa — the nearest US equivalent by yield and condition. |
| A737 Gr. B | ASTM / ASME | Near | Nb micro-alloyed vessel plate, yield 345 MPa, Rm 485–620 MPa. |
| P355GH | EN (European) | Near | 1.0473 (ex 19Mn6): EN 10028-2 non-fine-grain grade with the same strength; higher C (0.22), CEV 0.45. |
| S355N | EN (European) | Near | EN 10025-3 structural fine-grain twin without pressure-equipment certification. |
| Q345R / 16MnDR | GB/T (China) | Near | GB/T 713 Q345R: yield 345 MPa, Rm 510–640 MPa, impact 0 °C; 16MnDR (GB/T 3531) for −40 °C ≈ P355NL1. |
| 09G2S | GOST (Russia/CIS) | Near | GOST 5520 09G2S vessel plate: yield 305–345 MPa, Rm 460–490 MPa. |
| P355QH | EN (European) | Functional | EN 10028-6 quenched & tempered version for thick sections. |
Identical = same composition and mechanical limits within rounding. Near = one limit differs (e.g. carbon max or impact temperature). Functional = interchangeable for most uses after an engineering check. Full cross-reference for P355NH →
Old and superseded designations
| Old name | Standard | Note |
|---|---|---|
| WStE355 | DIN 17102 (withdrawn 1996) | W = warmfest (elevated temperature) → P355NH. |
| StE355 | DIN 17102 | → P355N (1.0562). |
| TStE355 | DIN 17102 | T = tieftemperatur → P355NL1 (−40 °C). |
| EStE355 | DIN 17102 | → P355NL2 (−50 °C). |
| Fe E 355 KG / KW / KT | EN 10028-3:1992 (ISO 9328) | |
| BS 1501-225-490B / LT | BS 1501 (withdrawn) |
Product forms and tolerance standards
Product forms: plate (EN 10028-3), seamless tube (EN 10216-3 P355NH), welded tube (EN 10217-3), forgings (EN 10222-4 P355QH), fittings (EN 10253-2).
Dimensional tolerances: plate: EN 10029; tube: EN 10216-3 / EN ISO 1127.
Key property values
P355NH yield strength
355 MPa (51.5 ksi) ≤ 16 mm, 345 MPa to 40 mm, 335 MPa to 60 mm, 315 MPa to 100 mm, 295 MPa to 150 mm. Elevated temperature (≤ 60 mm): 314 MPa at 100 °C, 284 at 200 °C, 250 at 300 °C, 210 MPa at 400 °C.
P355NH tensile strength
490–630 MPa (71–91 ksi) to 60 mm, 480–620 MPa to 100 mm, 470–610 MPa to 150 mm.
P355NH impact toughness
Transverse 27 J at −20 °C, 40 J at 0 °C, 55 J at +20 °C; P355NL1 27 J at −40 °C; P355NL2 27 J at −50 °C (and 40 J at −20 °C).
P355NH hardness
Not specified; normalized plate ≈ 150–190 HB. HAZ hardness after welding ≤ 350 HV with proper procedure; NACE MR0175 ≤ 22 HRC is met in the base metal.
Physical properties
Density 7.85 g/cm³, E = 212 GPa (20 °C), expansion 12.2 × 10⁻⁶/K (20–100 °C), conductivity ≈ 45 W/m·K.
Heat treatment
Delivery +N (normalized 890–950 °C or normalizing rolled). PWHT / stress relief 550–600 °C; do not exceed 620 °C (loss of Nb/V precipitation strengthening). Hot forming requires re-normalizing.
Weldability
Good weldability (CEV ≤ 0.43 %): E46/G46 low-hydrogen consumables; preheat per EN 1011-2 above ~25 mm (typically 75–125 °C). PWHT at 550–600 °C where the vessel code requires it (EN 13445 thickness thresholds, or H₂S/caustic service). Limit heat input to ~3.5 kJ/mm to keep HAZ toughness; for NL1/NL2 qualify procedures with impact tests at the design temperature.
Machining, forming and heat treatment
Machinability ≈ 60 % (similar to S355). Cold forming of heads and shells within EN 13445 limits (≤ 5 % strain without re-normalizing); hot forming 1050–900 °C then normalize 890–950 °C. Flame cutting with 100 °C preheat above 30 mm.
Typical applications
- LPG storage spheres, bullets and road tankers
- Air receivers and compressed-gas vessels
- Refinery and chemical process vessels, columns, separators
- Refrigerated gas storage (ammonia, propane, ethylene at −50 °C as P355NL2)
- Heat-exchanger shells and channels
- Seamless pressure tubes for boilers and pipelines (EN 10216-3)
- Hydraulic accumulators and high-pressure cylinders (as P355NH or P355QH)
Frequently asked questions
What is the difference between P355N, P355NH, P355NL1 and P355NL2?
Same chemistry and strength. N = normalized, impact 27 J at −20 °C; NH adds guaranteed yield up to 400 °C; NL1 guarantees 27 J at −40 °C; NL2 guarantees 27 J at −50 °C (with Ni ≤ 0.50 %). Choose by service temperature range.
Is P355NH the same as WStE355?
Yes. WStE355 (DIN 17102) became P355NH (1.0565) in EN 10028-3:1992. StE355 → P355N, TStE355 → P355NL1, EStE355 → P355NL2.
What is the ASTM equivalent of P355NH?
ASTM/ASME A537 Class 1 (normalized, 345 MPa yield) is the closest; A516 Grade 70 is commonly substituted but has only 260 MPa yield, so wall thickness must be re-checked.
What is the yield strength of P355NH at 400 °C?
210 MPa (≤ 60 mm). At 100/200/300 °C: 314/284/250 MPa.
Can P355NH be used below −20 °C?
Not on its own guarantee. Order P355NL1 (−40 °C) or P355NL2 (−50 °C); for −100 °C and below, nickel steels (EN 10028-4) are required.
Related grades
Verified against EN 10028-3:2017; EN 10028-3:2017 Tables 1–4; EN 10028-1:2017; ASME SA-516 / SA-537 (comparison). Last checked: September 2026.