The Short Answer
Yes, P235GH is a carbon steel. More precisely it is a non-alloy quality steel for pressure purposes, standardised in EN 10028-2. The letter P indicates pressure purposes, the number 235 is the minimum yield strength at room temperature in MPa, and the suffix GH shows that specified elevated temperature properties are guaranteed.
Where P235GH Sits in EN 10028-2
EN 10028-2 covers flat products of non-alloy and alloy steels with specified elevated temperature properties for pressure purposes. P235GH is the entry grade of that family: it is a low carbon, fine grain steel supplied as plate for boilers, pressure vessels, heat exchangers, storage tanks and associated pressure equipment. It is normally ordered as plate and then formed, rolled and welded into shells, heads and similar components.
Because the standard is written for pressure equipment rather than for general construction, the allowed stress values are tabulated across a temperature range, and impact properties are guaranteed. That is what distinguishes P235GH from a plain structural grade even where the yield strength is similar.
Chemical Composition
The composition is controlled to keep carbon low for weldability and to keep phosphorus and sulfur low for toughness. Typical limits are shown below.
| Element | Typical requirement, % |
|---|---|
| Carbon (C) | 0.16 max |
| Silicon (Si) | 0.35 max |
| Manganese (Mn) | 0.60 - 1.20 |
| Phosphorus (P) | 0.025 max |
| Sulfur (S) | 0.015 max |
| Aluminium (Al), total | 0.020 min for fine grain treatment |
| Nitrogen (N) | 0.012 max |
| Cr, Cu, Mo, Ni | Small residual limits only |
The aluminium addition and the nitrogen cap are what produce a fine grain structure, and the low sulfur level is what allows the grade to meet its impact requirement at room temperature.
Mechanical Properties
| Property | Typical requirement |
|---|---|
| Minimum yield strength ReH | 235 MPa for thinner plate, stepping down as thickness increases |
| Tensile strength Rm | 360 - 480 MPa |
| Elongation A | 24% min |
| Impact energy, Charpy V-notch | 27 J min at 20 degrees Celsius |
| Delivery condition | Normalised, or as agreed for the product form |
Yield strength is thickness dependent: a thin plate reaches the full 235 MPa, while heavier sections are permitted a lower minimum value as the section thickens. Those step-downs must be applied when the design calculation is made, because a vessel designed on the thin-plate value may not be valid for a thick-wall component.
P235GH and Related Grades Compared
| Grade | Standard | Minimum yield strength | Tensile strength |
|---|---|---|---|
| P235GH | EN 10028-2 | 235 MPa | 360 - 480 MPa |
| P265GH | EN 10028-2 | 265 MPa | 410 - 530 MPa |
| S235JR | EN 10025-2 | 235 MPa | 360 - 510 MPa |
| P295GH | EN 10028-2 | 295 MPa | 460 - 580 MPa |
S235JR is often quoted as an equivalent because it also reaches a 235 MPa minimum yield strength, but it is a structural steel under EN 10025-2 and is not supplied with the elevated temperature property set that pressure equipment design requires. P265GH and P295GH are the next steps up in strength within the same pressure family. For equivalents in other systems, P295GH is commonly compared with ASTM A516 Grade 70, a pressure vessel plate grade for similar service.
Applications and Fabrication
Boilers and steam systems: shells, drums and headers where moderate strength and good weldability are needed.
Pressure vessels and heat exchangers: plate components designed to the applicable pressure equipment code.
Storage tanks and process equipment: non-corrosive to mildly corrosive duties, with the corrosion allowance set by the designer.
Fabrication: readily formed cold and hot, welded with conventional carbon steel consumables, and normally supplied normalised for consistent toughness.
Because the grade is intended for pressure service, welding procedures, heat treatment and non-destructive examination are governed by the applicable design code, not by the material standard alone. Ordering information should therefore state plate thickness, delivery condition, required impact testing temperature and any code-required certification.
Frequently Asked Questions
Q: Is P235GH carbon steel or alloy steel?
It is a carbon steel: a non-alloy quality steel for pressure purposes, with only small residual limits on alloying elements.
Q: What does the GH suffix mean in P235GH?
It indicates that elevated temperature properties are specified, which is why the grade is used for pressure equipment design.
Q: What is the difference between P235GH and S235JR?
Both reach 235 MPa minimum yield strength, but P235GH is a pressure purpose plate grade under EN 10028-2 while S235JR is a structural grade under EN 10025-2.
Q: What is P235GH equivalent to in ASTM?
There is no exact match. Closest comparisons are made with ASTM A516 pressure vessel plate grades, with equivalence judged case by case.
Q: Why is the yield strength of P235GH shown as a range of values?
Because the guaranteed minimum yield strength decreases as plate thickness increases, so the value must be taken for the actual thickness.
Q: Is P235GH suitable for low temperature service?
Its impact requirement is set at room temperature, so low temperature duty needs a grade with guaranteed low temperature toughness.
