EN 10025-5 S355J2WP Weathering Steel Testing Requirements

Every S355J2WP plate comes with a mill certificate claiming it meets EN 10025-5. But what tests actually back that claim? Understanding the testing requirements helps you verify what you're buying and avoid costly mistakes.

Chemical analysis.

Every heat must be tested to confirm the alloying elements that make S355J2WP a weathering steel. Copper (0.25–0.55%), chromium (0.40–0.80%), and nickel (≤0.65%) are mandatory. Carbon, silicon, manganese, phosphorus, and sulfur are also checked. Without these elements in the right ranges, you don't have weathering steel—you have plain carbon steel with a forged label.

Tensile testing.

One tensile test per heat is standard. The test confirms minimum yield strength (355 MPa for plates up to 16mm), tensile strength (470–630 MPa), and elongation (≥20%). The test specimen is taken from the actual plate, so the results reflect real material, not just a recipe.

Impact testing (Charpy V-notch at -20°C).

The J2 designation requires Charpy impact testing at -20°C. Three specimens from the same plate are tested. The average must be at least 27J, with no single value below the standard's minimum. For plates under 10mm, subsize specimens are used with proportionally lower requirements. This test confirms the steel won't become brittle in cold weather.

Bend testing.

Not always mandatory, but often specified for formed components. The test bends a specimen 180° around a former. No cracks on the outside radius. This confirms ductility for forming and bending operations.

Ultrasonic testing (supplementary).

UT checks for internal defects like laminations, inclusions, or porosity. It's not required by EN 10025-5 but is commonly specified for critical applications—bridges, heavy load members, or parts with high welding demands. If your project needs UT, order it explicitly at the quoting stage.

Dimensional and surface checks.

Every plate is measured for thickness, width, length, flatness, and straightness to EN 10029 tolerances. Surface quality is visually inspected for laps, cracks, seams, or excessive scale. Heavy grinding beyond tolerance is a cause for rejection.

What the mill certificate must show:

Grade designation (S355J2WP)

Heat number (traceability to production batch)

Chemical analysis (heat analysis and product analysis)

Tensile test results (yield, tensile, elongation)

Impact test results (temperature -20°C, energy values, specimen size)

Reference to EN 10025-5

Mill name, certificate number, and date of issue

What to verify when the certificate arrives.

Impact temperature is -20°C—not 0°C, not room temperature

Copper, chromium, and nickel are within EN 10025-5 limits

Yield strength matches the thickness-dependent table (not always 355 MPa for thicker plates)

Heat number is consistent across all pages

Common oversights.

Assuming standard tests are always done (supplementary tests like UT or extra impact samples must be requested in advance)

Missing product analysis column—the test may only show heat analysis, but product analysis confirms the finished plate chemistry

Overlooking specimen size for Charpy tests (subsize specimens have lower energy requirements)

One practical tip. For critical applications, witness the testing or hire an independent lab to retest a sample from your delivered plates. The cost is small compared to the cost of a field failure.