P355GH steel (1.0473): properties, composition, equivalents
P355GH (1.0473, ex 17Mn4/HIII) is the top non-alloy grade of EN 10028-2: 355 MPa yield, 490–630 MPa tensile, guaranteed proof strength to 400 °C. Composition, elevated-temperature table, A516-70 comparison and why S355GH does not exist.
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What is P355GH?
P355GH is the strongest non-alloy grade in EN 10028-2 and the one specified when a pressure vessel has to carry more load than P265GH allows without moving to an alloyed or fine-grain steel. The G stands for *Gütestahl* qualities for pressure purposes and the H for elevated temperature: the standard publishes a guaranteed 0.2 % proof strength at 50 °C intervals up to 400 °C, and that table — not the room-temperature yield — is what a vessel designer calculates with.
The grade is a carbon-manganese steel: up to 0.22 % C with 1.10–1.70 % Mn, aluminium-killed and normalized. It is supplied mostly as plate from 5 to 150 mm, and also as seamless and welded tube, forgings and fittings, all carrying the same designation across EN 10216-2, EN 10222-2 and EN 10253-2 — which is why a complete vessel can be built in one grade.
A note on the name: S355GH does not exist. The S prefix belongs to structural steels in EN 10025, the P prefix to pressure steels in EN 10028. A drawing or enquiry that says S355GH almost always means P355GH, and a supplier who ships S355J2 against it has delivered a structural plate with no elevated-temperature data and no pressure certification.
P355GH chemical composition
| Element | Mass % | Note |
|---|---|---|
| C | ≤ 0.22 | ≤ 0.20 for thickness ≤ 16 mm |
| Si | ≤ 0.6 | |
| Mn | 1.1 – 1.7 | |
| P | ≤ 0.025 | |
| S | ≤ 0.015 | |
| Cr | ≤ 0.3 | |
| Cu | ≤ 0.3 | |
| Mo | ≤ 0.08 | |
| Ni | ≤ 0.3 | |
| Nb | ≤ 0.05 | |
| Ti | ≤ 0.03 | |
| V | ≤ 0.02 | |
| Al | ≥ 0.02 | total Al, for grain refinement |
Cr + Cu + Mo + Ni ≤ 0.70 %. The manganese range is what separates P355GH from P265GH: more Mn, more strength, slightly more care in welding.
P355GH 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) | 21 | ≈ 150–190 HB (typ.) |
| > 16 ≤ 40 mm, +N | 345 (50.0) | 490–630 (71.1–91.4) | 21 | |
| > 40 ≤ 60 mm, +N | 335 (48.6) | 490–630 (71.1–91.4) | 21 | |
| > 60 ≤ 100 mm, +N | 315 (45.7) | 480–620 (69.6–89.9) | 20 | |
| > 100 ≤ 150 mm, +N | 295 (42.8) | 470–610 (68.2–88.5) | 20 |
Transverse test pieces, normalized condition. Elevated-temperature proof strength is the reason the grade exists — see the properties section.
Impact toughness
P355GH requires a minimum Charpy V-notch energy of 27 J at −20 °C °C (longitudinal, ≤ 60 mm). 27 J at −20 °C longitudinal; 40 J at 0 °C on agreement. Above 60 mm the values are agreed at order.
P355GH equivalent grades
| Grade | System | Match | Why / differences |
|---|---|---|---|
| A516 Grade 70 | ASTM / ASME | Near | ASTM A516 Grade 70 (SA-516-70): yield 260 MPa (38 ksi), Rm 485–620 MPa. Similar tensile band and service role, but the yield is markedly lower and ASTM gives allowable stresses through ASME Section II-D rather than a guaranteed elevated-temperature proof strength. |
| SPV355 | JIS (Japan) | Near | JIS G3115 SPV355: 355 MPa yield pressure-vessel plate; chemistry and impact regime differ in detail. |
| A537 Cl. 1 | ASTM / ASME | Functional | Normalized C-Mn pressure plate with 345 MPa yield — the closest US grade by strength, used where A516-70 is not strong enough. |
| P355NH | EN (European) | Functional | EN 10028-3 weldable fine-grain grade at the same yield. Choose NH where low-temperature toughness matters more than elevated-temperature service; GH where the vessel runs hot. |
| 16Mo3 | EN (European) | Functional | Molybdenum-alloyed creep-resistant grade for service above 400 °C, where P355GH's guaranteed proof strength table ends. |
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 P355GH →
Old and superseded designations
| Old name | Standard | Note |
|---|---|---|
| 17Mn4 | DIN 17155 | the German boiler-plate designation replaced in 1992 |
| HIII | DIN 17155 | older trade name, still quoted in tenders |
| Fe 510 KW | EURONORM | withdrawn |
Product forms and tolerance standards
Product forms: plate (EN 10028-2, dominant), strip and sheet (EN 10028-2), seamless tube for pressure (EN 10216-2 as P355GH), welded tube (EN 10217-2), forgings (EN 10222-2 as P355GH), fittings (EN 10253-2).
Dimensional tolerances: Plate thickness to EN 10029 class A or B; flatness class N or S. Normalized (+N) delivery is standard above 16 mm..
Key property values
P355GH 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): 306 MPa at 100 °C, 278 at 200 °C, 235 at 300 °C, 196 MPa at 400 °C.
Tensile strength
490–630 MPa up to 60 mm, 480–620 MPa to 100 mm, 470–610 MPa to 150 mm. Elongation A ≥ 21 % (20 % above 60 mm), transverse.
Impact toughness
27 J at −20 °C longitudinal as standard to 60 mm. Transverse values and lower test temperatures are agreed at order; for genuinely low-temperature service the fine-grain P355NL1 or P355NL2 grades of EN 10028-3 are the correct choice.
Delivery condition
Normalized (+N) is standard and mandatory above 16 mm. Normalizing forming (+NR) is permitted by agreement. Simulated post-weld heat treatment data is supplied on request for vessels that will be stress-relieved.
Density and physical data
7.85 kg/dm³; modulus of elasticity 212 GPa at 20 °C, 199 GPa at 200 °C, 186 GPa at 400 °C; thermal conductivity ≈ 46 W/mK; specific heat ≈ 460 J/kgK.
Weldability
Readily weldable by all common processes. Carbon equivalent CEV ≤ 0.45 to 30 mm and ≤ 0.47 above, which puts preheat at 100–150 °C for thick sections and below 5 °C ambient. Use basic low-hydrogen consumables matched to the plate (for example E 46 4 B or S 46 4 for SAW); hydrogen control matters more here than on P265GH because the higher manganese raises hardenability in the heat-affected zone. Post-weld heat treatment at 530–620 °C is normal practice for pressure vessels and is required by most design codes above certain thicknesses; when PWHT is planned, order the plate with simulated PWHT test data so the mechanical values after heat treatment are documented rather than assumed.
Machining, forming and heat treatment
Machines like a normalized C-Mn steel at 150–190 HB: cutting speeds roughly 15 % below mild steel, carbide tooling, generous coolant on drilling. Oxy-fuel and plasma cutting are routine; the cut edge should be ground back 1–2 mm before welding on thick plate. Cold forming is possible but the bending radius should be at least 2.5 × thickness, and heavy cold work before PWHT needs to be declared because it affects the final properties.
Typical applications
- Pressure vessels, receivers and separators designed to EN 13445 or AD 2000
- Steam drums, headers and boiler shells below the creep range
- Heat exchanger shells and tube plates
- Refinery and petrochemical vessels operating to 400 °C
- Pipework and fittings in the same grade through EN 10216-2 and EN 10253-2
- Storage tanks for hot media where P265GH would need a thicker wall
Frequently asked questions
Is S355GH the same as P355GH?
S355GH is not a designation in any current standard. The S prefix is for structural steels (EN 10025), the P prefix for pressure steels (EN 10028). An enquiry for S355GH is almost always meant as P355GH — confirm it before ordering, because S355J2 plate carries no elevated-temperature data.
What is the difference between P265GH and P355GH?
Manganese and strength: P265GH has 0.50–1.40 % Mn and 265 MPa yield, P355GH has 1.10–1.70 % Mn and 355 MPa. At 400 °C the guaranteed proof strengths are 145 and 196 MPa, so P355GH lets a vessel wall be roughly a quarter thinner at the same pressure.
What is the ASTM equivalent of P355GH?
A516 Grade 70 is the usual substitution by service, but its yield is 260 MPa against 355 MPa. Where the design needs the yield rather than the tensile, A537 Class 1 at 345 MPa is closer.
Is P355GH the same as 17Mn4 or HIII?
Yes, in practice. 17Mn4 and HIII are the DIN 17155 designations replaced by P355GH in EN 10028-2; material certified to the EN grade satisfies an old 17Mn4 requirement.
Does P355GH need post-weld heat treatment?
Most pressure design codes require PWHT above a thickness threshold, typically 30–35 mm for C-Mn steels. Stress relieving at 530–620 °C is standard; order plate with simulated PWHT test data if the vessel will be heat treated.
Up to what temperature can P355GH be used?
The guaranteed proof strength table ends at 400 °C. Above that the grade is outside its design basis and a creep-resistant steel such as 16Mo3 or 13CrMo4-5 takes over.
Related grades
Verified against EN 10028-2:2017; EN 10028-2:2017 Table 4 and Table 6; EN 10029 (plate tolerances); EN 10204 (inspection documents). Last checked: September 2026.