Chemical Basis of the Grade
P265GH is a non alloy pressure vessel steel specified in EN 10028-2 under material number 1.0425. The steel is made as a fully killed, fine grain steel, produced by melting followed by secondary refining and vacuum degassing so that the oxygen, hydrogen and sulphur contents are low and the inclusion content stays at a level that supports toughness. The composition is deliberately simple: carbon is kept low enough to weld without difficulty, manganese provides the strength, and a small molybdenum addition, within the limits of the standard, improves the behaviour of the steel at elevated temperature and during long term service.
The G and H letters in the grade symbol are the reason the steel is ordered for boiler work. They record that elevated temperature properties are guaranteed and verified, so the design engineer can take allowable stresses from the high temperature tables of EN 10028-2 instead of relying on room temperature data alone.
Room Temperature and Elevated Temperature Properties
The room temperature requirements are the foundation of the grade. Yield strength is specified as a function of thickness, with a minimum of 265 MPa for the thin plate range and stepped values for thicker material, and the tensile strength range is 410 to 530 MPa with a minimum elongation of 22 percent on the tensile specimen. Those figures give the designer a predictable strength level together with enough ductility to form heads and shells.
| Property | Typical EN 10028-2 value for P265GH |
|---|---|
| Minimum yield strength | 265 MPa, thickness dependent |
| Tensile strength | 410 to 530 MPa |
| Minimum elongation | 22 percent |
| Delivery condition | Normalized |
| Elevated temperature data | Minimum proof strength tabulated up to 400 C |
| Dimensional tolerances | EN 10029, standard class unless otherwise ordered |
Above room temperature the significant property is proof strength rather than tensile strength. EN 10028-2 lists the minimum 0.2 percent proof strength values at a series of temperatures, and the allowable stress used in a boiler or vessel calculation is derived from those values. This is why the grade is used for components whose metal temperature is moderate but well above ambient: the strength is guaranteed and documented at the temperature that actually governs the wall thickness.
Forming, Welding and Low Temperature Behaviour
The normalized condition gives uniform grain size and stable properties, which shows up in the workshop as consistent bend behaviour. Cold bending of shells and dished heads is carried out without cracking on the common thicknesses, and cold flanging of nozzles and openings is routine. The low carbon and controlled carbon equivalent allow welding with ordinary low hydrogen consumables and standard procedures, although thick sections and high restraint joints still call for preheat and interpass control.
It is important not to confuse the letter G in the grade designation with an ultra low temperature application. The grade is a normal temperature and moderately elevated temperature pressure steel with verified high temperature data. Where equipment must operate well below zero, the design must be supported by impact testing at the minimum design metal temperature, and the plate is ordered with the impact requirements that the applicable design code specifies.
Inspection and Supply
Chemical analysis confirms the composition limits and the fine grain, fully killed practice of the heat.
Tensile testing at room temperature gives the yield strength, tensile strength and elongation for the delivered thickness.
Impact testing is performed where the design requires toughness verification, at the temperature stated in the order.
Thickness, width, length and flatness are checked against EN 10029, normally in the standard tolerance class.
Ultrasonic examination to EN 10160 is ordered for coded pressure equipment, with the acceptance class agreed in advance.
Inspection documents are issued to EN 10204 in the agreed form, with heat number traceability through to the finished component.
Storage practice supports the properties as well. Normalized plate should be kept on supports clear of the ground and handled so that edges and surfaces are not damaged, because surface defects on thin plate are hard to repair and can act as stress raisers in service.
Frequently Asked Questions
Q: What is the minimum yield strength of P265GH?
A: 265 MPa for the thin plate range, with stepped values for greater thickness as tabulated in EN 10028-2. The tensile strength range is 410 to 530 MPa.
Q: Why does the grade carry elevated temperature data?
A: Because the G and H letters in the designation indicate guaranteed and verified properties at high temperature. The proof strength values listed in the standard allow the allowable stress at the design metal temperature to be determined properly.
Q: How is the steel made?
A: As a fully killed fine grain steel, melted and then refined with secondary metallurgy and vacuum degassing so that sulphur, oxygen and hydrogen are low and the inclusion content is controlled.
Q: In which condition is the plate supplied?
A: Normalized, which gives uniform grain size and stable mechanical properties and supports reliable cold forming of heads, shells and nozzles.
Q: Can the plate be used at sub zero temperature?
A: Sub zero service has to be supported by impact testing at the minimum design metal temperature and by the impact requirements of the applicable design code, not by the elevated temperature designation of the grade.
