What Is P235GH Boiler Quality Steel Plate?
P235GH is a non-alloy, boiler quality steel plate supplied under the European pressure vessel plate standard EN 10028-2. In the designation, P stands for pressure vessel application, 235 is the minimum yield strength in MPa at room temperature, and GH marks a steel with specified properties at room temperature and at elevated temperature. The grade is one of the most widely used plate materials for boiler shells, pressure vessel shells, steam drums and heat exchanger components operating in the temperature range where a fine grain, weldable carbon steel is sufficient.
The performance of the grade comes from a carefully balanced chemistry rather than from alloy additions. Fine grain practice, controlled aluminium and nitrogen levels, and a normalized delivery condition give the plate a combination of strength, ductility and toughness that stays stable through forming, welding and long term service at elevated temperature.
Chemical Composition
Typical ladle analysis limits for P235GH plate are listed below. Aluminium is added for grain refinement and is specified with a minimum value, while nitrogen is capped so that free nitrogen does not impair toughness and ageing resistance.
| Element | Content (%) |
|---|---|
| C | 0.16 max |
| Si | 0.35 max |
| Mn | 0.60 - 1.20 |
| P | 0.025 max |
| S | 0.015 max |
| N | 0.012 max |
| Al | 0.020 min |
| Cr | 0.30 max |
| Cu | 0.30 max |
| Mo | 0.08 max |
| Nb | 0.02 max |
| Ni | 0.30 max |
| Ti | 0.03 max |
| V | 0.02 max |
Mechanical Properties
Because a pressure vessel shell is designed on allowable stress, the yield strength of P235GH is specified as a function of product thickness. The table below shows the minimum yield strength and the corresponding tensile strength range for the standard production thicknesses.
| Product thickness | Yield strength min (MPa) | Tensile strength (MPa) |
|---|---|---|
| up to 16 mm | 235 | 360 - 480 |
| over 16 mm to 40 mm | 225 | 360 - 480 |
| over 40 mm to 60 mm | 215 | 350 - 480 |
| over 60 mm to 100 mm | 200 | 340 - 480 |
| over 100 mm to 150 mm | 185 | 340 - 470 |
| over 150 mm to 250 mm | 175 | 330 - 470 |
Tensile testing is carried out at room temperature on every delivery, and elevated temperature proof strength testing is performed when it is specified in the order, because the allowable stress of a boiler component is governed by the hot strength of the steel rather than by its room temperature properties alone.
Performance Characteristics
Strength and toughness. P235GH combines a moderate yield strength with high ductility, which allows shells and domes to be formed and welded without the risk of cracking that comes with higher strength grades. The normalized condition refines the ferrite grain size and produces a uniform microstructure through the plate thickness.
Welding performance. The low carbon content and low carbon equivalent make the grade straightforward to weld by manual metal arc, submerged arc, gas metal arc and tungsten inert gas processes. Preheating is generally unnecessary for thin and medium sections, and post weld heat treatment is applied to relieve stresses in heavy or highly restrained fabrications rather than to restore properties.
Forming and machining. The plate can be sheared, flame cut, plasma cut, bent, rolled into shells and drilled with conventional workshop equipment. Cold forming of thick plate is carried out with respect for the minimum bend radius, and formed parts may be stress relieved afterwards.
Corrosion behaviour. P235GH is an unalloyed carbon steel and does not gain corrosion resistance from alloying, so it is used with coatings, linings or a corrosion allowance in aggressive service. Where the process medium is acidic, alkaline or chloride bearing, the appropriate protection system must be selected by the vessel designer rather than expected from the base metal itself.
Delivery Condition and Applications
P235GH plate is normally delivered normalized, and it can also be ordered hot rolled for applications where normalizing is not required by the design code. Plates are supplied cut to size, with sheared or machined edges, and with additional options such as ultrasonic examination, third party inspection and impact testing at low temperature.
Typical applications include:
Boiler shells, drums and headers
Pressure vessel shells, ends and nozzle reinforcement
Heat exchangers and steam condensers
Storage tanks and process vessels in chemical and petrochemical plants
Piping components and structural parts of fired equipment
FAQ about P235GH Boiler Quality Steel Plate
Q: Which standard covers P235GH plate?
P235GH flat products are specified in EN 10028-2, the European standard for flat products made of steels for pressure purposes with specified elevated temperature properties.
Q: What is the minimum yield strength of P235GH?
235 MPa for plate up to 16 mm thick, decreasing stepwise to 175 MPa for thicknesses above 150 mm up to 250 mm.
Q: What is the difference between P235GH and P265GH?
P265GH is the next grade up in the same standard, with a higher minimum yield strength of 265 MPa for thin plate and slightly higher carbon and manganese ranges.
Q: Is P235GH suitable for high temperature service?
Yes. The GH suffix indicates that properties at elevated temperature are specified, and the allowable stress at design temperature is taken from the elevated temperature proof strength values of the standard.
Q: How is P235GH plate delivered?
Plates are normally delivered in the normalized condition, either as rolled or normalized according to the order, with mill certificates and any supplementary inspection requirements recorded on the certificate.
Q: Does P235GH resist corrosion on its own?
No. It is a carbon steel, so corrosion resistance is provided by coatings, linings or a corrosion allowance specified by the designer for the particular process medium.
