Impact testing of structural plate: orientation, temperature and frequency

When a plate specification says “Charpy impact tested,” three separate questions still have to be answered:

1. At what temperature?
2. In which specimen orientation?
3. At what testing frequency or test-unit basis?

These are independent variables. Knowing the grade name alone does not always answer all three.

1. Test temperature

The Charpy test temperature is controlled by the material grade/quality and governing product standard, plus any project-specific requirement.

For common EN structural grades, toughness letters such as JR, J0, J2 and K2 are part of the grade-quality system. Fine-grain N/NL and M/ML families have their own toughness designations and requirements.

For the grade-name logic, see:

• JR, J0, J2 and K2 explained
• N, NL, M and ML explained

A project can impose a lower test temperature or additional toughness requirement. Therefore the PO/project specification always takes precedence over a generic assumption based only on the steel name.

2. Longitudinal vs transverse orientation

The orientation refers to the long axis of the Charpy specimen relative to the principal rolling direction of the plate.

• Longitudinal specimen — specimen axis parallel to rolling direction.
• Transverse specimen — specimen axis perpendicular to rolling direction.

Transverse values are often more demanding because rolled products can show directional differences in toughness.

Do not assume that a request for “CVN” automatically means transverse testing. The applicable product standard and purchase specification determine the required orientation.

If a project specifically requires transverse Charpy testing, write that requirement explicitly into the RFQ/PO and inspection plan.

3. Testing frequency

Impact-test frequency is a separate issue from temperature and orientation.

The governing standard normally defines testing through a test unit or sampling basis. Depending on the product standard and order, a test unit can be related to factors such as heat, grade, thickness range, delivery condition and quantity.

This means:

one set of Charpy results on an MTC does not necessarily mean that every individual plate was impact tested.

If the project requires one test per plate, per mother plate, per heat-treatment batch or another tighter frequency, that needs to be stated explicitly.

Thickness matters, but not in only one way

Plate thickness can affect several impact-test details:

• applicable mechanical-property table;
• sampling location;
• availability of full-size Charpy specimens;
• use of sub-size specimens where permitted;
• test-unit grouping.

Thickness by itself does not tell you the test temperature or orientation. Those still come from the governing grade/standard and purchase specification.

What does the Charpy test actually measure?

The conventional Charpy test measures the energy absorbed when a notched specimen fractures under pendulum impact.

ISO 148-1 specifies the Charpy pendulum impact test method for metallic materials. The product standard then tells you whether the test is required and what acceptance requirement applies to the grade/product.

So there are two layers:

• test method — how the Charpy test is performed;
• product requirement — temperature, orientation, energy and sampling requirements for the material being purchased.

What should appear on the MTC?

Where impact testing is required, a useful MTC review checks for:

• test temperature;
• specimen orientation;
• specimen size where relevant;
• individual and/or reported absorbed-energy values as required;
• traceability of the test unit to the supplied plate;
• governing product standard and grade.

Do not accept a row labelled only “Impact test: Pass” if the purchase specification requires detailed reported values.

Common procurement mistakes

“S355 means Charpy at one fixed temperature”

No. S355 is a strength family. The quality/delivery-condition suffix and product standard determine the toughness requirement.

“Thickness over 40 mm automatically means transverse CVN”

Not as a universal rule. Thickness can change property requirements and sampling, but orientation must be checked in the applicable standard/project specification.

“If the plate is UT tested, Charpy is covered”

No. EN 10160 UT addresses internal discontinuities. Charpy addresses impact toughness.

“One Charpy set means every plate was tested”

Not necessarily. Check the defined test unit and any project-specific frequency.

MetalMate takeaway

When reviewing impact requirements for structural plate, always separate temperature, orientation and frequency. Then check specimen size and acceptance energy. Treat each as an explicit requirement rather than assuming that “CVN tested” answers everything.

Related Knowledge

• JR, J0, J2 and K2 impact-toughness suffixes
• N, NL, M and ML delivery-condition families
• EN 10160 ultrasonic testing of steel plate

References

• ISO, ISO 148-1:2016 — Metallic materials — Charpy pendulum impact test — Part 1: Test method: https://www.iso.org/standard/63802.html
• NEN, EN 10025-2:2019 — Non-alloy structural steels: https://www.nen.nl/en/nen-en-10025-2-2019-en-262497
• NEN, EN 10025-3:2019 — Normalized/normalized rolled fine grain structural steels: https://www.nen.nl/en/nen-en-10025-3-2019-en-262498
• NEN, EN 10025-4:2019+A1:2022 — Thermomechanically rolled fine grain structural steels: https://www.nen.nl/en/nen-en-10025-4-2019-a1-2022-en-304866