EN 10222-2 Engineering Guide · Pressure Vessel Forgings
P305GH vs P265GH vs P355GH: Which Boiler Steel Grade Should You Specify?
📅 ⏱ 12-min read✍️ Jiangsu Liangyi Engineering Team🏭 ISO 9001:2015 · 27+ Years Experience
Bottom line: If your design temperature is between 300 °C and 450 °C and wall thickness exceeds 60 mm, P305GH is the correct specification in almost every case. P265GH is adequate for lighter sections below 300 °C. P355GH is reserved for the highest-stress, thickest-section applications where its tighter chemistry is justified. This guide gives you the EN 13445 data and metallurgical reasoning to decide with confidence.
Why Grade Selection Is More Consequential Than It Looks
Every EN 10222-2 pressure vessel steel grade carries the suffix "GH" — standing for Gewährleistete Hochtemperaturfestigkeit, meaning "guaranteed high-temperature strength." That guarantee distinguishes these grades from ordinary structural steels and makes the choice between them technically binding, not just commercial.
P265GH, P305GH, and P355GH are the three grades most commonly confused in procurement. They appear similar on a data sheet but differ in ways that become critical at elevated temperatures, in thick sections, or under cyclic loading. Specifying the wrong grade creates two equally bad failure modes:
Under-specification leads to creep damage, stress-relief cracking after PWHT, or premature fatigue failure — occurring after the equipment has passed hydrostatic test and entered service.
Over-specification (P355GH where P305GH would suffice) adds testing costs, longer lead times, and higher material cost with no engineering return.
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Scope of this guide
We cover forgings produced to EN 10222-2:2017. Plate products (EN 10028-2) and seamless tubes (EN 10216-2) use the same grade designations but with different property tables. Always cross-check the applicable product standard for your form factor. If you are sourcing P305GH open die forgings and seamless rolled rings, our product page covers the full shape range, dimensional limits, and MTC options.
Metallurgy
Chemical Composition — Where the Grades Actually Diverge
All three grades are carbon-manganese steels sharing a broadly similar base chemistry. The differences are subtle on paper but decisive in service. Higher manganese controls hardenability and creep ductility; the carbon equivalent (CE) drives weldability; and tighter sulphur limits in P305GH translate directly into measurable Charpy impact energy gains at −20 °C.
Table 1: Chemical composition limits per EN 10222-2:2017 Table 1. CE per IIW formula: C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15.
Element
P265GH (1.0425)
P305GH (1.0436)
P355GH (1.0473)
Engineering significance
C max %
0.20
0.17 ↓ lowest
0.22
Lower C in P305GH improves weldability; higher C in P355GH raises yield strength
Mn %
0.80 – 1.40
1.10 – 1.50 ↑
1.10 – 1.60
Higher Mn floor in P305GH/P355GH increases hardenability and creep ductility
Si max %
0.40
0.40
0.40
Identical across all three grades
P max %
0.025
0.025
0.025
Same limit in spec; quality producers achieve <0.012% actual via VD + ladle refining
S max %
0.020
0.015 ↓
0.015
Tighter S in P305GH/P355GH improves transverse toughness — critical for thick forgings
Al min %
0.020
0.020
0.020
Grain-refining aluminium — mandatory for fine austenite grain in all three grades
CE (IIW) max
0.43
0.42 ↓ lowest
0.45 highest
P305GH has the lowest CE specification — most weld-friendly of the three
Source: EN 10222-2:2017 Table 1.
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Common misreading on weldability
Many buyers assume P265GH has better weldability because its carbon ceiling is 0.20%. In reality, P305GH's carbon maximum is lower (0.17%), and its manganese floor is higher. This produces a finer-grained, tougher microstructure after normalizing. At the top of specification, P305GH has a lower carbon equivalent than P265GH.
Properties
Mechanical Properties by Grade and Section Thickness
EN 10222-2 specifies mechanical properties as a function of nominal thickness. Note how yield strength drops as section size increases — this is the thickness penalty from insufficient hardenability, and the primary engineering argument for P305GH or P355GH over P265GH in heavy-walled forgings above 60 mm.
P265GHMat. No. 1.0425 · EN 10222-2
ReH (≤ 16 mm)≥ 265 MPa
ReH (100–150 mm)≥ 215 MPa
Rm410 – 530 MPa
A min22%
KV at 0 °C≥ 27 J
Max service temp.350 °C
P305GHMat. No. 1.0436 · EN 10222-2
ReH (≤ 16 mm)≥ 305 MPa
ReH (100–150 mm)≥ 255 MPa
Rm460 – 580 MPa
A min20%
KV at −20 °C≥ 27 J
Max service temp.450 °C
P355GHMat. No. 1.0473 · EN 10222-2
ReH (≤ 16 mm)≥ 355 MPa
ReH (100–150 mm)≥ 280 MPa
Rm490 – 630 MPa
A min20%
KV at −20 °C≥ 27 J
Max service temp.480 °C
✓
Section thickness penalty — key takeaway
Between ≤16 mm and 100–150 mm sections, P265GH loses 50 MPa of yield (−19%), P305GH also loses 50 MPa (−16%). But in absolute terms, P305GH at 150 mm still delivers 255 MPa — 18% more than P265GH at the same thickness. In heavy-walled forgings, the grade gap widens rather than narrows.
High-Temperature Performance
Elevated-Temperature Strength — EN 13445 Allowable Stress Data
The service temperature limits in EN 10222-2 correspond to the temperature at which creep strength drops below the safety factor required by EN 13445, ASME, or AD-Merkblatt design calculations. The table below extracts allowable stress values from EN 13445-2 Annex B — the values your pressure vessel design engineer uses when sizing wall thickness.
Table 2: Allowable stress f (MPa) from EN 13445-2 Annex B Table B.1-2. Reference section ≤ 16 mm. Apply thickness correction factor for heavier sections per EN 13445-2.
Temperature
P265GH f (MPa)
P305GH f (MPa)
P355GH f (MPa)
P305GH vs P265GH
20 °C
177
203
237
+15%
100 °C
157
192
222
+22%
200 °C
139
175
200
+26%
300 °C
122
157
181
+29%
350 °C
113
148
170
+31%
400 °C
~103 (near limit)
138
158
+34%
450 °C
Not rated
120
140
—
480 °C
Not rated
Not rated
120
—
*P265GH guidance value only above 350°C; not recommended for sustained pressure service without specific design justification.
The allowable stress advantage of P305GH over P265GH grows at higher temperatures — from +15% at ambient to +34% at 400 °C. This translates directly into a proportional wall thickness reduction that more than offsets the modest material cost premium between grades.
Fabrication
Weldability — Preheat, CEV, and PWHT Requirements
Many engineers assume P265GH has an inherent weldability advantage. In practice, P305GH's lower carbon ceiling (0.17% vs 0.20%) gives it a lower maximum CEV (0.42 vs 0.43) — meaning it can often be welded with the same or lesser preheat. The actual heat chemistry on the mill test certificate is always the controlling variable.
Parameter
P265GH
P305GH
P355GH
Max CEV (spec)
0.43
0.42 (lowest)
0.45 (highest)
Preheat — t ≤ 25 mm
None typically
None typically
50 – 75 °C
Preheat — t 25–60 mm
50 °C min
50 °C min
75 – 100 °C
Preheat — t > 60 mm
75 °C min
75 °C min
100 – 150 °C
PWHT requirement
Optional ≤ 35 mm
Optional ≤ 35 mm
Mandatory > 30 mm
PWHT temperature
580 – 620 °C
600 – 640 °C
600 – 650 °C
Recommended filler metal
ER70S-6 / E7018
ER70S-6 / E7018
ER80S-D2 / E8018-D1
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PWHT temperature control — thick P305GH sections
For wall thicknesses above 80 mm, maintain PWHT temperature within 600–640 °C. The standard permits up to 680 °C, but Ac1 for P305GH is approximately 720 °C — the margin is narrower than the specification implies. Exceeding 650 °C on heavy sections risks localised softening at the weld HAZ. Specify temperature and hold time explicitly on the purchase order and WPS — never just reference "per EN 10222-2."
Metallurgical Process
Heat Treatment Conditions — +N, +NT, and +QT
EN 10222-2 permits three supply conditions: Normalized (+N), Normalized and Tempered (+NT), and Quenched and Tempered (+QT). The table maps the recommended condition to section and grade.
Section Thickness
P265GH
P305GH
P355GH
≤ 35 mm
+N or +NT
+N or +NT
+NT or +QT
35 – 80 mm
+NT preferred
+NT preferred
+NT or +QT
80 – 150 mm
+NT
+NT mandatory
+NT
> 150 mm
+NT only
+NT only
+NT only
Practical +QT limit
≤ 50 mm (water) / ≤ 80 mm (polymer)
≤ 50 mm (water) / ≤ 80 mm (polymer)
≤ 80 mm (water) / ≤ 100 mm (polymer)
All three grades lack the alloy additions (Cr, Mo, Ni) needed to develop martensitic microstructure at mid-thickness above 80–100 mm. A P305GH forging above 100 mm specified as +QT will show +NT properties at the core regardless of what the certificate states — the physics of heat transfer cannot be overridden by a document.
Real-World Usage
Application Selection — Which Grade Belongs Where
P265GH
Steam drum nozzle pads (t ≤ 40 mm)
Low-pressure steam below 300 °C, light wall. P265GH is adequate and the most economical choice here.
P305GH
Boiler drum manhole flanges (t 60–120 mm)
Cyclic thermal loading, design temperature 380–430 °C, wall above 60 mm. P305GH is the correct choice — P265GH cannot meet yield targets at this section and temperature combination.
P305GH
Heat exchanger tube sheets (Ø up to 4,500 mm)
Tube-pitch drilling creates complex stress fields. P305GH's finer grain and improved transverse toughness under +NT condition gives more reliable notch-root performance than P265GH.
P355GH
High-pressure boiler feedwater pump casings
Discharge pressures above 200 bar, section 100–180 mm. P355GH's higher yield strength reduces wall thickness and total casing weight while maintaining code safety factors.
P265GH
Low-pressure condensate valve bodies (DN50–DN150)
Condensate temperature below 200 °C, low pressure. P265GH is often over-specified here but acceptable — the maximum grade justified by engineering requirements.
P355GH
Supercritical steam valve bodies
250 bar / 480 °C — at the ceiling of P355GH's rating. P355GH is the final C-Mn grade before transitioning to 16Mo3, P11, or P22 for supercritical applications.
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Manufacturer product page
Jiangsu Liangyi Co., Limited manufactures P305GH open die forgings and seamless rolled rings from 30 kg to 30,000 kg, including single-piece tube sheets up to Ø 4,500 mm × 350 mm thick. EN 10204 3.1 MTC is issued as standard; EN 10204 3.2 inspection can be arranged through a customer-nominated third-party inspection body. For the full shape range, dimensional limits, and a 24-hour custom quote, see our 1.0436 (P305GH) forged parts page.
Specification Tool
Grade Decision Guide — Five Questions That Determine Your Answer
Grade Selector — EN 10222-2
Q1: What is your maximum design temperature?
Below 300 °C
P265GH is sufficient for most applications in this temperature range
300 °C – 450 °C
P305GH is the standard specification — covers the majority of boiler and pressure vessel applications
450 °C – 480 °C
P355GH — or consider 16Mo3 for temperatures approaching 530 °C
Q2: What is the nominal wall thickness of your forging?
≤ 40 mm
All three grades viable — let design temperature decide
40 mm – 120 mm
P305GH or P355GH; P265GH loses too much yield strength at this section
> 120 mm
P305GH +NT or P355GH +NT only — +QT is not viable at this mass
Q3: Is this a fatigue-cycled application (manhole, nozzle, valve under thermal cycling)?
No — static load
Grade choice driven by temperature and thickness alone
Yes — cyclic
P305GH or P355GH forging required; grain flow raises fatigue strength 20–30% vs plate
Unknown
Treat as cyclic — upgrading to P305GH costs far less than a fatigue failure in service
Q4: What Mill Test Certificate level does your project require?
EN 10204 3.1
All three grades available with 3.1 MTC as standard — no constraint on grade selection
EN 10204 3.2
Issued by a third-party inspection body nominated by you — confirm arrangements before order placement
ASME / API code
Verify cross-reference with your authorised inspection authority: P305GH ≈ ASTM A350 LF2 Cl.1 in many (not all) applications
Q5: Is total project cost a primary constraint?
Cost-sensitive
P265GH where temperature permits; P305GH for 300–450 °C; avoid P355GH unless the engineering requirement demands it
Performance-critical
Select by engineering requirement — grade premium between P265GH and P305GH is typically <8% of total forging cost
Long-term plant lifecycle
Factor in creep inspection intervals — P305GH often has the lower 20-year lifecycle cost in the 300–450 °C service range
Frequently Asked
Common Questions from Engineers and Procurement Teams
Only if your design temperature is below 300 °C and nominal section thickness is under 40 mm. At higher temperatures or thicker sections, P265GH will not meet the time-dependent (creep) strength requirements mandated by EN 13445. A substitution that passes room-temperature tensile testing may still fail during a PED compliance audit — the allowable stress tables in EN 13445-2 Annex B will flag the deficit at elevated temperature immediately. Document any substitution formally with written acceptance from the responsible design engineer and, where applicable, the notified body.
P305GH (material number 1.0436) is rated to a maximum service temperature of 450 °C under EN 10222-2. The EN 13445-2 allowable stress at 450 °C is 120 MPa for sections up to 16 mm (with thickness reduction factors for heavier sections). Above 450 °C, the carbon-manganese family loses creep strength rapidly and you should consider 16Mo3 (rated to approximately 530 °C by addition of molybdenum) or 13CrMo4-5 / P11 for applications approaching 550 °C.
There is a practical overlap for many applications — both are carbon-manganese forgings for pressure service with Charpy impact testing. However, they are not formally equivalent. Chemistry ranges differ; impact test temperatures differ (P305GH tests at −20 °C under EN 10222-2, while A350 LF2 tests at −46 °C under ASTM A350); and the allowable stress tables under EN 13445 and ASME Section VIII use different safety factor methodologies. Always verify cross-material equivalency through your authorised inspection authority or notified body before substituting in a coded application.
16Mo3 (material number 1.5415) adds approximately 0.25–0.35% molybdenum to the base carbon-manganese chemistry. Molybdenum significantly improves creep resistance by pinning grain boundaries and retarding carbide coarsening at elevated temperature. 16Mo3 is rated to approximately 530–540 °C versus P305GH's 450 °C ceiling. If your design temperature is between 450 °C and 530 °C, 16Mo3 is the natural next step — no exotic alloy additions are required, and weldability remains good with appropriate preheat.
For P305GH forgings above 100 mm nominal wall thickness, Normalized and Tempered (+NT) is the mandatory and only viable supply condition. Quenched and Tempered (+QT) is not technically achievable above approximately 80 mm because P305GH lacks the chromium, molybdenum, and nickel content needed to develop through-thickness martensite at that mass. A P305GH forging exceeding 100 mm specified as +QT will exhibit +NT properties at mid-thickness regardless of what the certificate states, because the physics of heat transfer do not permit full martensite transformation at that section size.
Jiangsu Liangyi Co., Limited issues EN 10204 Type 3.1 inspection certificates as standard on all P305GH forgings. EN 10204 Type 3.2 — which requires validation by an inspection body independent of the manufacturer — can be arranged when the customer nominates a third-party inspection body such as SGS, Bureau Veritas, or TÜV Rheinland. The 3.2 certificate is issued by that independent body, not by Jiangsu Liangyi. Please specify your MTC requirement at the time of inquiry so we can confirm scope and cost.
P305GH is a carbon-manganese steel susceptible to high-temperature hydrogen attack (HTHA) at elevated hydrogen partial pressures. For service above approximately 7 bar H₂ partial pressure and 230 °C, the Nelson curves in API RP 941 apply. At those conditions, P305GH falls outside the safe operating envelope and chrome-moly grades (1.25Cr-0.5Mo or 2.25Cr-1Mo) are required. For low-pressure hydrogen service below the API RP 941 Nelson curve limits, P305GH may be used with appropriate PWHT and hardness controls per NACE MR0175 / ISO 15156.
JL
Jiangsu Liangyi Engineering Team
Jiangsu Liangyi Co., Limited · Jiangyin, Jiangsu, China · Est. 1997
Jiangsu Liangyi Co., Limited is an ISO 9001:2015 certified manufacturer of open die forgings and seamless rolled rings, specialising in EN 10222-2 pressure vessel steels, stainless steels, and nickel alloys. With 27+ years of forging experience and 120,000 t/year production capacity, we supply EPC contractors, pressure vessel fabricators, valve OEMs, and engineering firms in 50+ countries. All technical content on this page is authored by our in-house engineering team based on practical manufacturing experience and published EN/ASTM standards.
ISO 9001:2015EN 10204 3.1 (Standard)27+ Years50+ Countries120,000 t/year
Jiangsu Liangyi Co., Limited has manufactured EN 10222-2 P305GH open die forgings and seamless rolled rings since 1997. From 30 kg valve bodies to 30,000 kg tube sheets — EN 10204 3.1 MTC as standard, 3.2 third-party inspection arrangeable, 24-hour RFQ response.