What S355J0WP Weather Resistant Steel Is
S355J0WP is a structural weathering steel defined in EN 10025-5, the part of the European standard that covers technical delivery conditions for structural steels with improved atmospheric corrosion resistance. The designation breaks down into a minimum yield strength of 355 MPa, an impact test temperature of 0 °C, and a phosphorus-alloyed composition indicated by the letter P.
The grade is supplied mainly as hot rolled plate and is further formed into profiled sheets, cladding panels and fabricated sections. In service it is normally left unpainted. Exposed alternately to rain and air, the surface develops a dense oxide layer that adheres tightly to the steel, restricts further oxygen access and slows the corrosion rate to a fraction of that of ordinary structural steel.
The WP family is distinguished from the W family by chemistry rather than by strength. Phosphorus is the principal alloying addition, which raises the corrosion resistance economically in thinner sections. The trade-off is that phosphorus also raises the ductile-to-brittle transition temperature, so the grade is normally specified for sheet and plate in moderate thicknesses and is not intended for heavy sections or for low-temperature impact duty.
Chemical Composition
Typical ladle analysis for the phosphorus-alloyed weathering grades of EN 10025-5 is shown below. Limits are maximum values unless a range is given.
| Element | S355J0WP / S355J2WP |
|---|---|
| C | 0.12 max |
| Si | 0.75 max |
| Mn | 1.00 max |
| P | 0.06 - 0.15 |
| S | 0.030 max |
| Cu | 0.25 - 0.55 |
| Cr, Ni and other additions | May be added to meet the corrosion requirement |
Compared with the W grades, the phosphorus content is deliberately much higher and the carbon content is capped lower to compensate. This combination gives good strength with acceptable toughness in thin and medium gauges, and it is the reason the WP grades are frequently selected for roofing, cladding and formed components rather than for heavy welded structures.
Mechanical Properties
| Property | S355J0WP (t ≤ 16 mm, typical specified minimum) |
|---|---|
| Minimum yield strength ReH | 355 MPa |
| Tensile strength Rm | 470 - 630 MPa |
| Elongation A | 22 % minimum, longitudinal |
| Impact energy | 27 J at 0 °C for the J0 variant; 27 J at -20 °C for the J2 variant |
Yield and tensile values fall as thickness increases, so the allowable stress should always be read from the table for the actual plate gauge rather than from the headline 355 MPa figure. The J0 and J2 suffixes indicate impact test temperature only; the two variants share the same chemistry and corrosion behaviour.
Plate and Panel Size Range
| Item | Range |
|---|---|
| Thickness | 0.5 mm (cold rolled sheet) up to 200 mm (hot rolled plate) |
| Width | 600 - 3000 mm, or as required |
| Length | 4 - 12 m, or cut to order |
| Thickness tolerance | Normally ±0.1 mm for sheet and closer control on request |
| Technique | Hot rolled for plate, cold rolled for sheet |
| Surface treatment | Clean, shot blasted or painted to customer specification |
| Export packing | Waterproof paper and steel strip, seaworthy package suitable for all transport modes |
Fabrication and Welding Notes
Use welding consumables matched to the weathering grade so that the weld metal weathers at a rate similar to the parent plate.
Keep heat input under control and avoid excessive grain growth, since high phosphorus content reduces toughness in the heat affected zone.
Remove weld spatter and slag completely; residues hold moisture and become corrosion initiation sites.
Form panels with generous bend radii, since the grade has lower ductility than plain carbon structural steel.
Design for drainage and air circulation; standing water and trapped moisture prevent the protective oxide layer from forming.
Cut edges exposed to weather develop the same patina as the rolled surface, so edge protection is normally unnecessary.
Applications of S355J0WP Plate and Panels
Roofing, cladding and profiled facade panels on buildings and stations.
Bridge parapets, sign gantries and highway furniture.
Railway rolling stock components and wagon bodies.
Containers, silos and hoppers exposed to the atmosphere.
Landscape architecture, planters, screens and decorative structures.
Industrial ducting, fan housings and chimney cladding.
The grade is chosen whenever a long maintenance interval matters more than initial material cost. Because no paint system is required, inspection and repainting work is eliminated for decades, which is a decisive advantage on structures with difficult access.
FAQ
Q: What does the designation S355J0WP mean?
S355 indicates a minimum yield strength of 355 MPa, J0 indicates impact testing at 0 °C, and W with P indicates an atmospheric corrosion resistant steel alloyed mainly with phosphorus.
Q: What is the difference between S355J0WP and S355J0W?
The WP grade is alloyed with 0.06 - 0.15 % phosphorus and is used in thinner sections, while the W grade restricts phosphorus and relies on chromium, nickel and copper additions for heavier plate.
Q: Can S355J0WP be welded?
Yes, using matching weathering steel consumables and controlled heat input; because of the phosphorus content the grade is normally limited to moderate thicknesses.
Q: Does the plate need to be painted?
No. The grade is designed for bare exposure, where it forms a protective oxide layer; painting is only required for appearance reasons or in strongly acidic environments.
Q: What sizes are available?
Cold rolled sheet from 0.5 mm and hot rolled plate up to 200 mm, in widths of 600 - 3000 mm and lengths of 4 - 12 m, with cut-to-length service.
Q: How is the steel packed for shipment?
Standard seaworthy export packing with waterproof paper and steel strip, suitable for container, break bulk and rail transport.
