Longitudinal vs transverse Charpy orientation

A Charpy result is not fully defined by its temperature and absorbed energy. You also need to know the orientation of the test piece relative to the principal direction of working or rolling.

That is the distinction behind longitudinal and transverse CVN specimens.

Longitudinal specimen

A longitudinal test piece has its long axis taken parallel to the principal direction of working/rolling of the product.

For rolled plate, this normally means the specimen axis runs in the rolling direction.

Transverse specimen

A transverse test piece has its long axis taken transverse to the principal direction of working/rolling.

For plate, this normally means the specimen axis is perpendicular to the rolling direction in the plane of the plate.

ISO 377 provides the general framework for location and preparation of samples/test pieces, while the applicable material/product standard determines which orientation is required for the order.

Why orientation changes the result

Rolled steel is not perfectly isotropic. Rolling elongates the microstructure and non-metallic inclusions, and the resulting directional structure can influence toughness.

In many rolled steels, transverse Charpy energy is lower than longitudinal energy. That is a useful general expectation, not a universal conversion rule. Steelmaking cleanliness, reduction ratio, rolling route, thickness, microstructure and inclusion control can all affect the difference.

Therefore:

80 J longitudinal cannot automatically be treated as 80 J transverse.

If the specification requires transverse CVN, a longitudinal result does not demonstrate the same requirement unless the governing document explicitly allows it.

Specimen axis and notch orientation are different concepts

A common source of confusion is using “transverse” to describe both the specimen direction and the notch direction.

The specimen longitudinal axis tells you how the test piece is oriented relative to rolling. The notch orientation/location describes how the V-notch is positioned in the specimen/product and, for weld testing, where the notch samples parent metal, weld metal or HAZ.

Those descriptions should not be mixed.

Plate, sections and pipe can use different conventions

For plate, rolling direction is normally clear. For rolled sections and tubular products, sampling direction and location can be defined differently by the product standard because the geometry and manufacturing direction differ.

Always read the product-specific sampling clause rather than carrying a plate convention across to every product form.

What to ask when an MTC just says “Charpy”

If orientation matters to the project, ask for confirmation of:

• test-piece axis: longitudinal or transverse;
• sampling location;
• test temperature;
• specimen size;
• individual/average energy results;
• governing standard and test unit.

See Charpy V-notch testing: the essentials for the broader test framework.

Procurement takeaway

Treat orientation as part of the Charpy requirement itself. A result can have the correct temperature and energy but still fail the specification if it was taken in the wrong direction.

References and verification sources

• ISO 377:2017 — Location and preparation of samples and test pieces
• ISO 148-1:2016 — Charpy pendulum impact test