1. Charpy V-Notch Impact Test (CVN) at Low Temperatures
Purpose:
Measures fracture toughness to prevent brittle failure in cold environments.
Required due to Grade E's use in polar waters and high-stress zones.
LR Requirements:
Minimum absorbed energy: 27J at -40°C (vs. 0°C for Grade B).
Test frequency: One set per heat treatment batch (LR Rules, Pt.3, Ch.2.4).
Sample orientation: Transverse (most stringent condition).
Testing Method:
ASTM E23 / ISO 148-1 standard.
Three specimens tested per batch; average must meet 27J, with single value ≥20J.
Why Critical?
Ensures structural integrity in Arctic operations where ductile-to-brittle transition is a risk.
2. Tensile Testing (Yield Strength, Tensile Strength, Elongation)
Purpose:
Confirms mechanical strength and ductility.
LR Grade E vs. Ordinary Steel:
| Property | LR Grade E | Ordinary (Grade B) |
|---|---|---|
| Yield Strength (min) | 355 MPa | 235 MPa |
| Tensile Strength | 490-620 MPa | 400-520 MPa |
| Elongation (min) | 21% (GL ≥50mm) | 22% (GL=5.65√So) |
Test Procedure (ISO 6892-1 / ASTM A370):
Full-thickness specimens tested in longitudinal and transverse directions.
Strain rate control for accurate yield point detection.
Why Critical?
Ensures load-bearing capacity in heavy hull sections.
3. Bend Testing (Ductility Verification)
Purpose:
Evaluates weldability and formability without cracking.
LR Requirements:
180° bend test with mandrel diameter = 3× thickness (for t ≤ 20mm).
No cracks >3mm allowed after bending.
Test Types:
Face bend (weld face in tension).
Root bend (weld root in tension).
Why Critical?
Ensures fabrication suitability for complex hull shapes.
4. Ultrasonic Testing (UT) for Internal Defects
Purpose:
Detects laminations, inclusions, and voids that weaken structural integrity.
LR Requirements:
100% automated UT scanning for plates ≥15mm thick.
Acceptance criteria: No indications >50mm in length.
Testing Method:
Shear-wave UT for subsurface flaws.
Calibration blocks with artificial defects (e.g., side-drilled holes).
Why Critical?
Prevents catastrophic failure from undetected internal flaws.
5. Chemical Composition Analysis (CEV & Pcm Control)
Purpose:
Ensures weldability and strength consistency.
Key Elements (LR Grade E vs. Ordinary Steel):
| Element | LR Grade E (Max %) | Grade B (Max %) |
|---|---|---|
| Carbon (C) | 0.18 | 0.21 |
| Sulfur (S) | 0.025 | 0.035 |
| Phosphorus (P) | 0.025 | 0.035 |
Carbon Equivalent (CEV) Limits:
CEV ≤ 0.43% (IIW formula) to prevent cold cracking.
Pcm ≤ 0.25% (Japanese formula) for better weldability.
