BW-FI-AFR-019: Anaerobic Black Spot Corrosion in West Africa

Critical Finding: Standard sea‑freight packaging fails catastrophically during prolonged congestion at Lagos ports. After 45+ days at 90%+ RH, anaerobic black spot corrosion penetrates the zinc layer. Only Vertical Eye‑to‑Wall (VEW) sealed packaging eliminates the humid, oxygen‑depleted microenvironment responsible for this failure.

This case study investigates the recurrent black spot corrosion on galvanized steel coils stranded at Apapa & Tin Can Island ports, Lagos. Through root‑cause analysis of the unique West African logistics chain, we establish a mandatory packaging upgrade that has proven zero‑defect delivery in over 200 shipments.

The Lagos Port Reality: A Corrosion Accelerator

Apapa and Tin Can Island ports in Lagos are notorious for extreme congestion, particularly during the rainy season (April–October). Coils routinely sit exposed to 90–95% relative humidity for 45–60 days awaiting clearance. Under these conditions, standard seaworthy packaging becomes a liability.

Conventional packs use a PE film wrap and desiccant bags. While effective in ventilated holds, the trapped air inside the coil’s eye quickly becomes stagnant. The combination of high humidity, warmth, and restricted air exchange creates an anaerobic microenvironment where sulfate‑reducing bacteria thrive and electrochemical reactions proceed without atmospheric oxygen renewal. The result is a distinct black corrosion product (magnetite and iron sulfide) that pits the zinc and steel.

Why Standard Packaging Fails in West Africa

Desiccant absorbs moisture initially, but their capacity is finite. Once saturated, the sealed environment becomes a condensation trap. The eye cavity is particularly vulnerable because it holds the core temperature longer, promoting cold‑wall condensation. Black spot corrosion is the visible symptom of a completely overwhelmed protection system.

The Vertical Eye‑to‑Wall (VEW) Sealing Solution

Baosteel company’s VEW packaging re‑engineers the coil protection for extreme tropical logistics. Instead of relying on desiccant, the coil is secured with the eye axis vertical and the entire package is hermetically sealed to the pallet wall. This configuration:

• Eliminates the stagnant eye cavity – air cannot circulate, but more importantly, no humid external air can enter once sealed.
• Prevents condensation by equalizing the dew point across the sealed volume through a controlled atmosphere (nitrogen purge optional).
• Delivers zero corrosion after 120+ days of tropical exposure in independent third‑party testing.

Since adopting VEW for all West African shipments, our clients have recorded zero rust claims on over 200 shipments, even when clearance extended beyond 90 days.

Stop Paying for Port Delays with Your Coil Quality

Upgrade to VEW sealed packaging and eliminate the chronic black spot problem from your Nigerian supply chain. Baosteel company integrates this into your production flow with no extra lead time impact.

IF Destination = West Africa (Lagos/Apapa)
   AND Expected Dwell Time > 30 Days
THEN Vertical Eye‑to‑Wall Sealed Packaging
     + Nitrogen Purge (Optional)
ELSE Standard Seaworthy Packaging