P355N is a weldable, normalized fine-grain steel plate specified in EN 10028-3 for pressure vessel applications. It provides high yield strength, good tensile properties, dependable impact resistance, and acceptable corrosion resistance, which is why it is one of the most widely used pressure vessel steels in Europe. Normalizing refines the grain structure and stabilizes the mechanical properties through the thickness, making the plate reliable for welded fabrication. This article covers the composition, mechanical properties, dimensions, and equivalents of P355N.
Overview of EN 10028-3 P355N Steel
EN 10028-3 covers weldable fine-grain steels for pressure purposes in the normalized delivery condition, including the P275, P355, and P460 families, which are distinguished by minimum yield strength for plates up to 16 mm thick and by impact test temperature. The N in P355N indicates the normalized or normalized-rolled condition. Within the grade, the sub-grades NH, NL1, and NL2 guarantee impact energy at 0 degrees Celsius, minus 20 degrees Celsius, and minus 40 degrees Celsius respectively, allowing designers to match the steel to the service temperature.
Chemical Composition and Carbon Equivalent
The maximum composition of P355N is carbon 0.20 percent, silicon 0.50 percent, manganese 0.90 to 1.70 percent, phosphorus 0.030 percent, and sulfur 0.025 percent. Nitrogen is limited to 0.020 percent, and the aluminum minimum of 0.020 percent supports fine-grain treatment. Microalloy limits are chromium 0.30 percent, copper 0.30 percent, molybdenum 0.08 percent, niobium 0.005 percent, nickel 0.50 percent, titanium 0.03 percent, and vanadium 0.10 percent. The carbon equivalent, calculated as carbon plus manganese over six plus the sum of chromium, molybdenum, and vanadium over five plus the sum of nickel and copper over fifteen, remains low enough for normal welding procedures.
Mechanical Properties by Thickness
For plates up to 35 mm thick, the minimum yield strength is 355 MPa and the tensile strength is 490 to 630 MPa with 22 percent minimum elongation. The yield strength steps down to 345 MPa for 35 to 50 mm, 325 MPa for 50 to 70 mm, 315 MPa for 70 to 100 mm, and 295 MPa for 100 to 150 mm, with tensile strength 470 to 610 MPa and 450 to 590 MPa respectively for the thicker ranges. Minimum impact energy in the standard grade is 40 J at minus 20 degrees Celsius, 47 J at 0 degrees Celsius, and 55 J at plus 20 degrees Celsius, with the NH, NL1, and NL2 sub-grades guaranteeing performance at their respective test temperatures.
Typical Dimensions
P355N plates are commonly available in thicknesses from 6 mm to 300 mm, widths from 1500 mm to 4050 mm, and lengths from 3000 mm to 15000 mm. The wide dimension range covers everything from small dished ends to large vessel shells and heat exchanger plates. Exact availability depends on the mill's rolling program, and dimensional tolerances should be verified against EN 10029.
Equivalent Grades and Applications
International equivalents of P355N include Fe E355 in European nomenclature, A St52 in Germany, A52CP in France, Fe510-1-KW in Italy, SS 21 06 01 in Sweden, and SPV 355 in Japan. These equivalents are not automatically interchangeable, because testing rules and sub-grades differ, so each should be verified against the applicable standard. P355N is widely used for pressure vessels, boiler drums, storage tanks, heat exchangers, and pipework components that require good strength combined with reliable low-temperature impact properties.
Frequently Asked Questions
1. What does the N in P355N mean?
The N indicates the normalized or normalized-rolled delivery condition, which refines the grain structure and stabilizes mechanical properties.
2. What is the difference between P355N, P355NH, P355NL1, and P355NL2?
They share the same strength and composition basis but guarantee impact energy at different temperatures: NH at 0 degrees Celsius, NL1 at minus 20 degrees Celsius, and NL2 at minus 40 degrees Celsius.
3. What is the minimum yield strength of P355N?
The minimum yield strength is 355 MPa for plates up to 35 mm thick, decreasing with thickness to 295 MPa for the 100 to 150 mm range.
4. What impact energy does P355N guarantee?
The standard grade guarantees minimum impact energy of 40 J at minus 20 degrees Celsius, 47 J at 0 degrees Celsius, and 55 J at plus 20 degrees Celsius.
5. What thickness range is available?
P355N plates are available from 6 mm to 300 mm thick, in widths of 1500 to 4050 mm and lengths of 3000 to 15000 mm.
6. Which international grades are equivalent to P355N?
Equivalent designations include Fe E355, A St52, A52CP, Fe510-1-KW, SS 21 06 01, and SPV 355, though each must be checked against its own standard before substitution.