What Is P235 and Why Look for Equivalents?
P235 is the designation for a family of European pressure-vessel steels covered by EN 10028-2. The number 235 is the minimum yield strength in megapascals at room temperature for thickness up to 16 mm. The most widely used member of the family is P235GH, where GH indicates a grade for elevated-temperature service that is suitable for pressure equipment such as boilers, storage tanks and piping. Because EN grades are often specified on international projects but fabrication may take place in a country using a different standard system, engineers need a reliable mapping from P235 to the equivalent national grades for substitution, certification and inspection purposes.
Core Equivalent Materials
Q245R (GB/T 713) for Pressure Vessels
P235GH is closely matched to Q245R, the Chinese pressure-vessel plate steel, in chemical composition and mechanical properties. Q245R is particularly suitable for medium- and elevated-temperature pressure equipment such as boiler shells, storage tanks and reactors. The two grades have similar yield levels, and both are intended for welded pressure construction.
20G and 20MnG (GB/T 5310) for Boiler Tubes
For seamless pipe applications, P235GH corresponds to 20G (carbon steel boiler tube) or 20MnG (manganese-strengthened boiler tube) used in high-pressure boiler piping systems. The tube forms are used in water-wall, economizer and header circuits where the operating temperature is moderate.
ASTM A283 Gr.C for General Structural Service
In general structural steel work, the yield strength of P235 (235 MPa) is close to that of ASTM A283 Gr.C (205 MPa). However, the applicable temperature range and the design rules differ, so this mapping is only appropriate for non-pressure, ambient-temperature structures.
Comparison of Key Parameters
| Parameter | P235 (EN 10028-2) | Q245R (GB/T 713) | 20G (GB/T 5310) |
|---|---|---|---|
| Yield strength, min | 235 MPa (t <= 16 mm) | 245 MPa (t <= 16 mm) | 225 MPa |
| Tensile strength | 360 - 480 MPa | 400 - 520 MPa | 375 - 500 MPa |
| Carbon content, max | 0.16 % | 0.20 % | 0.24 % |
| Manganese content | 0.60 - 1.20 % | 0.50 - 1.00 % | 0.35 - 0.65 % |
The table shows that P235GH is the most tightly controlled of the three in carbon content, which is why it welds predictably and behaves well at elevated temperature. Q245R offers a slightly higher yield, while 20G is a tube-specific steel whose strength comes from a higher carbon content and thermomechanical treatment.
Differences in Application Scenarios
Q245R
Core use: domestic pressure vessels, storage tanks, reactors and boiler drums, with a design temperature range of about -20 deg C to +475 deg C. Limitation: not recommended for low-temperature service below -20 deg C or above 475 deg C; other grades are needed for cryogenic or ultra-high-temperature duty.
20G / 20MnG
Core use: high-pressure boiler heating-surface tubes, steam pipelines and power-station headers, with working temperature up to about 450 deg C. Advantage: welding performance is better than Q245R in thin-wall tube form, and the grades are optimized for complex welded tube circuits.
ASTM A283 Gr.C
Core use: general structural plates and non-pressure fabrications at ambient temperature. Limitation: no elevated-temperature design values and no impact-test requirement, so it cannot substitute for P235GH in pressure equipment.
Standards and Process Requirements
The route by which each grade is made explains part of the difference in properties. P235GH normally requires electric arc furnace or converter steelmaking with secondary refining outside the furnace, and the plate is delivered in the normalized condition by default. Q245R allows a conventional continuous-casting route and may be supplied hot rolled or normalized. 20G boiler tube requires controlled rolling and controlled cooling, and the tube is delivered normalized and tempered. When substituting one grade for another, verify the delivery condition, the impact-test temperature and the inspection documents, because these are often the real differentiators between nominally similar steels.
Selection Guidance
Choose Q245R when the equipment is a Chinese-coded pressure vessel or tank and the design temperature is within -20 to 475 deg C. Choose 20G or 20MnG when the item is a seamless boiler tube for high-pressure circuits. Choose ASTM A283 Gr.C only for non-pressure structural applications. When the project is designed to EN codes, use P235GH itself and avoid substitution unless the local code explicitly accepts the equivalent grade. Confirm the equivalence with the mill certificate, not with a name-only comparison.
Frequently Asked Questions
What is the difference between P235 and P235GH?
P235 is the family name in EN 10028-2; P235GH is the specific grade with guaranteed elevated-temperature properties and tighter requirements, intended for pressure equipment. In practice, P235 in pressure applications means P235GH.
Can Q245R replace P235GH directly?
For pressure vessels within -20 to 475 deg C, Q245R is a recognized equivalent in terms of strength and weldability, but substitution must be confirmed by the design code and the client, because allowable stresses at temperature, impact test temperatures and inspection levels differ between GB and EN practice.
Is P235GH weldable without special measures?
Yes, P235GH has a low carbon equivalent and is one of the easiest pressure-vessel steels to weld. Preheating is generally not required for thin sections, but for thick walls, low ambient temperatures or highly restrained joints, a moderate preheat and controlled heat input are recommended.
What is the maximum service temperature of P235GH?
The EN 10028-2 standard provides design values up to a defined temperature limit, and the practical maximum for the grade is around 400 - 475 deg C depending on thickness and stress level. Above that, creep-resistant alloy steels such as 15CrMoG or the equivalent EN grades must be used.
Does 20G boiler tube have the same yield strength as P235GH?
No. The minimum yield of 20G is about 225 MPa in thin-wall tube form, slightly below the 235 MPa of P235GH plate. The tensile strength range, however, is comparable. Tube circuits are designed using the tube-specific allowable stresses from the applicable code, so a direct strength comparison between plate and tube grades is not the deciding factor.
Which standard governs P235GH inspection documents?
EN 10028-2 specifies the product, while the inspection documents follow EN 10204, typically with a 3.1 certificate issued by the mill. For pressure equipment, the notified-body requirements of the relevant code or directive also apply.