Answer
When inspecting a water ballast tank (WBT) with an attending surveyor (e.g., during an intermediate, annual, or special renewal survey), your structure must demonstrate meticulous safety management and specific structural targeting.
Pre-Inspection & Safety Preparation (Non-Negotiable)
Risk Assessment & Permit Isolation: Issue a comprehensive Enclosed Space Entry Permit and lock out/tag out (LOTO) all ballast pumps and cross-flooding lines connected to the tank.
Atmosphere Validation: Ventilate the tank completely and test the atmosphere at multiple levels (top, middle, bottom) using calibrated gas detectors. Ensure oxygen content is at exactly (O2 at 21%, LEL at 0%, CO at 0%, Chlorine – 0 ppm( max permissible limit- 0.5 ppm)
Access & Communication: Ensure illumination is set up (explosion-proof LED string lights) and establish a dedicated stand-by watchkeeper at the hatch with a portable VHF radio, a rescue harness, and an EEBD.
Technical & Structural Checkpoints During Inspection
You and the surveyor will look for structural degradation, primarily focusing on high-stress concentration zones:
Anodes and Cathodic Protection: Inspect the wasting rate of sacrificial zinc/aluminum anodes. If more than 50% is consumed, note them for replacement.
Coatings Condition: Assess the hard protective epoxy coating for breakdown, blistering, or detachment. Scale the damage according to Class categories: Good, Fair, or Poor.
Structural Deflections & Stress Points: Closely examine the connections of transverse bulkheads, longitudinal stiffeners, floors, side stringers, and beam knees. Look for localized buckling, hairline cracking, or micro-fractures in high-stress areas like the upper and lower turn of the bilge.
Wastage & Pitting Corrosion: Check for deep pitting corrosion on horizontal plates where water traps, particularly along the bottom plating and tank boundaries.
Stripping & Air Pipes: Inspect the condition of the internal suction bell-mouth, strums, sounding pipes (striking plates), and air vent configurations for physical damage or blockages.