What P235GH and P265GH Have in Common
P235GH and P265GH are non-alloy quality steels for pressure purposes, supplied as flat products under the European standard EN 10028-2, which covers steels with specified elevated temperature properties. Both grades are delivered in the normalised condition, both are intended for welded pressure equipment such as vessels, boilers and heat exchangers, and both are chosen for their combination of moderate strength, good ductility and predictable high temperature behaviour. The gh suffix marks the elevated temperature property route, so these grades are ordered whenever a design code requires proof strength values at service temperature rather than only at room temperature.
The difference between them comes down to strength level. P265GH is the stronger grade and is specified when the design pressure, diameter or temperature pushes the wall thickness beyond what the lower grade can carry economically.
Both are non-alloy, weldable pressure steels supplied in the normalised condition.
Both are specified with 0.2% proof strength values at elevated temperatures for design calculations.
Both are used for shells, heads, nozzles and tube plates in welded pressure equipment.
Chemical Composition and Carbon Equivalent
| Element (max, %) | P235GH | P265GH |
|---|---|---|
| Carbon (C) | 0.16 | 0.20 |
| Silicon (Si) | 0.35 | 0.40 |
| Manganese (Mn) | 0.60-1.20 | 0.80-1.40 |
| Phosphorus (P) | 0.025 | 0.025 |
| Sulphur (S) | 0.015 | 0.015 |
The clearest compositional difference is carbon: about 0.16% maximum in P235GH against about 0.20% in P265GH, with manganese raised in the stronger grade to develop the extra strength. Because carbon and manganese are the two elements that drive both strength and hardenability, they also drive the carbon equivalent, and that is why the welding behaviour of the two steels differs even though both are classed as readily weldable. Sulphur and phosphorus are held to the low levels expected of pressure steels, which protects toughness and reduces the risk of hot cracking and lamellar defects in thick welded joints.
Mechanical Properties
| Property | P235GH | P265GH |
|---|---|---|
| Minimum yield strength | 235 MPa | 265 MPa |
| Tensile strength | 360-500 MPa | 410-570 MPa |
| Typical carbon content | about 0.16% | about 0.20% |
| Delivery condition | Normalised | Normalised |
The 30 MPa gap in minimum yield strength is what the design engineer works with. On a large diameter vessel, moving from P235GH to P265GH can reduce the required wall thickness and therefore the weight and welding volume of the shell, which is often the deciding factor on a project. The reverse trade is ductility and weldability: with less carbon, P235GH retains higher elongation and lower hardenability, so it tolerates welding with a simpler procedure, fewer preheat requirements and less risk of a hard heat affected zone.
Elevated Temperature Performance
Both grades belong to the EN 10028-2 family precisely because they carry specified proof strength values above room temperature, which allows a design to be verified against the relevant pressure equipment code at the actual metal temperature rather than with a room temperature allowable. The stronger grade does not automatically have better high temperature strength in relative terms, since the design calculation uses the absolute values tabulated for each grade and thickness. In practice, the choice between them at elevated temperature is made on the required wall thickness and on the temperature limits set by the applicable design code, and both are commonly used in boiler and heat exchanger service where the metal temperature stays within the range the standard tabulates.
P235GH: heat exchangers, low pressure boilers, low temperature and low pressure pipeline systems for fluids and gases.
P265GH: high pressure steam boilers, pressure vessels and industrial pipelines carrying hot fluids.
Weldability and Fabrication
P235GH is the easier of the two to weld. Its lower carbon content keeps the carbon equivalent down, so thinner sections can normally be welded without preheat, and the resulting heat affected zone is softer and more forgiving. P265GH remains a weldable pressure steel, but its higher carbon and manganese mean a higher carbon equivalent, so a qualified welding procedure will typically specify preheat, interpass temperature control and sometimes post-weld heat treatment on thick sections. Both grades are supplied normalised, and that condition should be preserved in fabrication: heavy hot forming or welding that effectively re-austenitises a component may call for re-normalising to restore the specified properties before the final pressure test.
Qualify the welding procedure for the actual grade and thickness rather than relying on the parent steel designation alone.
Control heat input to protect toughness in the heat affected zone of the stronger grade.
Keep the mill certificate for each plate so that the proof strength values used in design remain traceable to the delivered material.
Confirm the applicable rules for preheat and post-weld heat treatment when thickness increases.
FAQ: P235GH and P265GH
Q: What is the difference between P235GH and P265GH?
P265GH is the stronger grade, with a minimum yield strength of 265 MPa against 235 MPa for P235GH, and a higher tensile band of 410-570 MPa against 360-500 MPa.
Q: Which grade is easier to weld?
P235GH. Its carbon content of about 0.16% against about 0.20% in P265GH gives a lower carbon equivalent, so preheat is less often needed and the heat affected zone is more forgiving.
Q: Are P235GH and P265GH the same as ASTM A516 grades?
They are European non-alloy pressure steels under EN 10028-2, while ASTM A516 is a separate specification. A substitution between them must be checked against the applicable design code and the specified strength and temperature data.
Q: What condition are these plates supplied in?
Both grades are normally supplied in the normalised condition, which is what gives them their predictable strength and toughness for pressure equipment.
Q: When should P265GH be selected instead of P235GH?
When the design pressure, diameter or temperature requires more strength than P235GH can provide within an acceptable wall thickness, or when a lighter vessel is a project priority.
Q: Can the two grades be welded to each other?
Yes, dissimilar joints between them are common. The welding procedure should be qualified for the stronger grade and for the thickness involved, with consumables selected to match the lower strength side.
