EN 10025-5 S355J2WP Weathering Steel Plate Testing Requirements Explained

S355J2WP doesn't arrive on site with a simple "good enough" stamp. It comes with a mill certificate that proves the material meets EN 10025-5. But what tests actually back up that certificate? Here's what happens in the lab and what you should check.

Chemical analysis – every heat.

Every production heat undergoes spectrographic analysis to verify alloy chemistry. Key elements checked: carbon, silicon, manganese, phosphorus, sulfur, copper, chromium, and nickel. The test ensures copper stays at 0.25–0.55%, chromium at 0.40–0.80%, and nickel at ≤0.65%. Without these, you don't have weathering steel.

Tensile testing – per heat and thickness.

Tensile tests confirm yield strength, tensile strength, and elongation. One test per heat is standard, but multiple tests may be required for different thickness ranges. The test specimen is machined from the actual plate. Results must meet EN 10025-5 minimums for the ordered thickness.

Impact testing – the J2 requirement.

Charpy V-notch testing at -20°C is mandatory. Three specimens are tested from the same plate location. The average must be at least 27J, with no single value below the standard's acceptable minimum. For thinner plates (under 10mm), subsize specimens are used with proportionally lower requirements. The test temperature and energy values must be clearly stated on the certificate.

Bend testing – when required.

Not always mandatory, but often specified for formed parts or certification. The test bends a specimen 180° around a former of specified diameter. No cracks on the outside radius. This confirms ductility and forming capability.

Ultrasonic testing – supplementary but recommended.

UT to EN 10160 checks for internal defects—laminations, inclusions, or porosity. Not required by the grade standard, but often specified for critical applications (bridges, pressure parts, heavy load members). If you need UT, specify it at the time of ordering.

Dimensional inspection – every plate.

Thickness, width, and length are measured to EN 10029 tolerances. Flatness and straightness also checked. Heavy grinding of surface defects beyond EN 10029 limits is cause for rejection.

Surface quality inspection – visual check.

Visual inspection catches laps, cracks, seams, or excessive scale. For weathering steel, surface condition is especially critical because the patina forms on the as-rolled surface. Heavy scarfing or grinding can remove the chemistry-rich outer layer, delaying patina formation.

What the certificate must show.

Grade designation (S355J2WP)

Heat number

Plate dimensions

Chemical analysis (heat and product analysis)

Tensile test results (yield, tensile, elongation)

Impact test results (temperature, energy values, specimen size)

EN 10025-5 reference

Mill name and certificate number

Lateral "DWT" (drop-weight tear) testing is not standard for EN 10025-5. If your project requires it, specify it separately—most mills don't run it by default.

Practical tip for buyers.

When the certificate arrives, don't just file it. Verify:

Impact test temperature is -20°C (not 0°C or room temperature)

Copper and chromium are present and within specified limits

Yield strength matches the standard table for your plate thickness

Certificate number and heat number are consistent across all pages