1. Controlled Preheating Techniques
ABS mandates preheating for steels with high carbon equivalents (CEV > 0.38%) or thicknesses > 25mm to avoid hydrogen-induced cracking (HIC).
Temperature Ranges:
AH36: 50–100°C
EH40: 100–150°C
Thick Plates (>50mm): Up to 200°C
Methods:
Electric resistance heating mats for uniform heat distribution.
Localized flame heating for small repairs.
Monitoring: Infrared thermometers ensure compliance with ABS Table 4-3 (Preheat Requirements).
Preheating slows cooling rates, reducing HAZ brittleness. ABS requires preheat records for audit trails.
2. Low-Hydrogen Welding Consumables
ABS prohibits cellulose-based electrodes (e.g., E6010) for high-strength steels, requiring low-hydrogen processes:
Filler Metals:
SMAW: AWS E7018 (for AH/DH36)
FCAW: AWS E81T1-Ni2 (for EH40)
SAW: Flux-wire combinations with ≤4ml/100g diffusible hydrogen.
Storage: Electrodes must be stored in 110–150°C ovens to prevent moisture absorption.
Certification: ABS-approved consumables (e.g., ABS-Approved 3Y45) undergo rigorous diffusible hydrogen testing (<5ml/100g).
Mismatched filler metals can cause undermatching (weak welds) or overmatching (residual stress).
3. Joint Design and Groove Preparation
ABS requires bevel angles, root gaps, and back-gouging tailored to plate thickness and steel grade:
V-Groove vs. U-Groove:
Thickness < 20mm: 60° V-groove (single-sided weld).
Thickness > 40mm: 20° U-groove (reduces weld volume by 30%).
Back-Gouging: Mandatory for complete joint penetration (CJP) welds in critical zones (e.g., hull seams). Carbon arc gouging must be followed by grinding to remove HAZ carburization.
Misalignment Tolerance: ABS limits angular distortion to ≤3° and peak-to-peak offset to ≤10% of plate thickness.
Laser scanning is increasingly used to verify joint geometry pre-weld.
4. Post-Weld Heat Treatment (PWHT)
For thick sections (>50mm) or high-restraint joints, ABS requires PWHT to relieve residual stresses:
Stress Relieving:
Temperature: 580–620°C for AH36; 600–650°C for EH40.
Duration: 1 hour per 25mm thickness.
Methods:
Furnace PWHT for large subassemblies.
Local induction heating for onsite repairs.
Documentation: ABS requires time-temperature charts certified by third-party inspectors.
PWHT also improves toughness in the HAZ, critical for Arctic-class vessels.
5. Non-Destructive Testing (NDT) Protocols
ABS mandates multi-method NDT based on joint criticality:
Radiographic Testing (RT): For full-penetration welds in Grade D/EH steels (per ABS Ch.6, Sec.2).
Ultrasonic Testing (UT): Detects subsurface flaws in thick-plate butt welds (≥15mm). Phased-array UT (PAUT) is now ABS-approved for higher accuracy.
Magnetic Particle Testing (MT): For fillet welds in high-stress zones (e.g., bracket connections).
Acceptance Criteria: ABS rejects welds with cracks, lack of fusion, or slag inclusions >4mm.
Automated NDT (e.g., robotic UT crawlers) is gaining traction to reduce human error.
Conclusion
ABS-compliant welding demands procedural rigor, from preheat controls to advanced NDT. Shipyards investing in automated welding (e.g., FCAW robots) and digital QA systems achieve both compliance and cost efficiency.
