What P275NH Steel Plate Is
P275NH is a weldable fine grain pressure vessel steel supplied in the normalised condition and specified in EN 10028-3, the part of the European flat product standard for pressure purposes that covers weldable fine grain steels in the normalised condition. The designation is self describing: P stands for pressure vessel steel, 275 is the minimum specified yield strength in megapascals at the thinner sizes, N means normalised delivery, and H means the steel is impact tested at minus 20 degrees Celsius. The material number is 1.0487.
Grades in the same series differ only in impact test temperature: P275N is tested at 0 degrees Celsius, P275NH at minus 20 degrees Celsius, P275NL1 at minus 40 degrees Celsius and P275NL2 at minus 50 degrees Celsius. All four share the same strength and composition framework, so the choice between them is made on the minimum design metal temperature of the equipment.
Mechanical Properties Specified in EN 10028-3
| Nominal thickness | Minimum yield strength ReH (MPa) | Tensile strength Rm (MPa) |
|---|---|---|
| Up to 16 mm | 275 | 390 to 510 (up to 60 mm) |
| Over 16 to 40 mm | 265 | 390 to 510 |
| Over 40 to 60 mm | 255 | 390 to 510 |
| Over 60 to 100 mm | 235 | 370 to 490 |
| Over 100 to 150 mm | 225 | 360 to 480 |
| Over 150 to 250 mm | 215 | 350 to 470 |
Minimum elongation after fracture is 24 % for thicknesses up to 60 mm and 23 % above 60 mm. Normalising produces a uniform ferritic pearlitic structure and a fine grain size, which is why the grade is used for vessels where a predictable, isotropic property set is required. Because impact energy requirements are stated at the test temperature associated with the suffix letter, a substitution between suffix variants must be supported by the actual test temperature recorded on the inspection document.
Chemical Composition Limits
| Element | Limit (%) | Element | Limit (%) |
|---|---|---|---|
| C | 0.16 max | Mo | 0.08 max |
| Si | 0.40 max | Nb | 0.05 max |
| Mn | 0.80 to 1.50 | Ti | 0.03 max |
| P | 0.025 max | V | 0.05 max |
| S | 0.015 max | Al total | 0.020 min |
| Cr | 0.30 max | N | 0.012 max |
| Cu | 0.30 max | Nb + Ti + V | 0.05 max |
Aluminium is deliberately added as a grain refining element and a minimum total aluminium content is required, while the niobium, titanium and vanadium additions are capped, because micro alloying changes the weldability and the impact behaviour of a normalised pressure steel. Carbon equivalent and weldability are further controlled through the low carbon and manganese range.
Equivalent and Comparable Grades
There is no single worldwide equivalent for P275NH, because equivalence for pressure equipment depends on which property governs the design. The closest ASTM grade is A516 Grade 60, a carbon steel plate for pressure vessels with a minimum yield strength of 220 MPa and a tensile range of 415 to 550 MPa, widely used for similar service at moderate temperature. Within the same European standard family, P265GH of EN 10028-2 sits in the same strength band and is the more familiar choice where impact testing at 0 degrees Celsius is sufficient.
| System | Comparable designation | Comment |
|---|---|---|
| ASTM | A516 Grade 60 | pressure vessel plate, comparable strength level |
| EN 10028-2 | P265GH | non alloy grade, impact tested at 0 degrees Celsius |
| GB | Q245R | normalised pressure vessel plate, nearest Chinese grade |
Older national designations of the same strength class, such as the German DIN 17155 grades and the former British pressure vessel plate grades, have been withdrawn in favour of EN 10028-3 and should not be used for new orders.
How to Select and Specify an Equivalent
Substitution between equivalent grades is an engineering decision, not a commercial one. The comparison should cover five items: the design temperature and the required impact test temperature, the allowable stress derived from the specified minimum yield strength at the governing thickness, the thickness range covered by the alternative standard, the inspection document type, and any additional requirement such as ultrasonic testing or a maximum carbon equivalent for welding.
In practice a fabricator replacing P275NH with another normalised pressure plate should confirm that the alternative is accepted by the design code and the notified body, that the tensile range overlaps, and that the impact test is carried out at a temperature at least as low as that required by the equipment specification.
Frequently Asked Questions
Q: What material is equivalent to P275NH steel plate?
A: The nearest ASTM grade is A516 Grade 60, the nearest Chinese grade is Q245R, and within EN 10028 the related grade P265GH of part 2 occupies the same strength band. None of these is a direct drop in substitute without engineering review.
Q: What does the H in P275NH mean?
A: H denotes that the steel is impact tested at minus 20 degrees Celsius in the normalised condition, as required by EN 10028-3.
Q: What is the yield strength of P275NH?
A: The minimum yield strength is 275 MPa up to 16 mm and decreases with thickness, reaching 215 MPa for thicknesses over 150 mm to 250 mm.
Q: What is the minimum elongation of P275NH?
A: 24 % for thicknesses up to 60 mm and 23 % for thicknesses over 60 mm.
Q: Is P275NH the same as P275NL1?
A: No. The strength and composition framework is the same, but P275NL1 is impact tested at minus 40 degrees Celsius, so it is the appropriate choice for colder service.
Q: Which applications use P275NH plate?
A: Pressure vessels, boilers, storage tanks, heat exchangers and structural pressure parts where a normalised fine grain steel with verified low temperature toughness is required.
