Hopper Corrosion Coating at Durban Harbour: Why Epoxy Fails Under Impact
Hopper corrosion coating at port and bulk handling facilities faces a challenge that most coating specifications ignore — impact. Conventional epoxy coatings protect against corrosion under static conditions, but hoppers at working ports experience continuous impact from bulk material loading on the inside. That impact transmits through the steel wall and cracks rigid epoxy coatings on the outside, creating exactly the moisture pathways that cause the corrosion the coating was meant to prevent. This case study documents the application of SI-COAT 579 CM to a hopper at Durban Harbour, KwaZulu-Natal, in June 2024, and the three-month inspection results that followed.
Location: Durban Harbour, KwaZulu-Natal, South Africa
Industry: Port and bulk materials handling
Environment: Marine coastal — high salt aerosol, high humidity, continuous impact loading
Product: SI-COAT 579 CM — Ansi Grey
Application date: 18–20 June 2024
Three-month inspection: 27 September 2024
The Problem: Epoxy Cracking Under Impact at Durban Harbour
The hopper at Durban Harbour presented a corrosion protection problem that the existing epoxy coating could not solve. Epoxy had been applied to the exterior steel as a standard corrosion protection measure. However, the continuous impact of bulk materials loading into the hopper from the inside transmitted vibration and shock forces through the steel wall. Epoxy is a rigid, brittle coating. It cannot absorb repeated dynamic loading. Under these conditions, the impact transmission caused the epoxy coating on the outside of the hopper to crack.
Once cracking begins in an epoxy film, the consequences accelerate quickly. Cracks in the coating surface allow moisture to penetrate directly to the steel substrate. In Durban Harbour’s marine environment — constant salt aerosol, high humidity, and the aggressive coastal corrosion category that KwaZulu-Natal’s Atlantic-facing port infrastructure experiences — moisture reaching bare steel through coating cracks initiates rapid corrosion. The coating had failed not because of inadequate adhesion or poor application, but because its chemistry was wrong for the mechanical demands of the environment.
The fundamental issue is modulus. Epoxy cures to a high-modulus, rigid film. When the steel substrate moves — under impact, vibration or thermal cycling — the coating cannot follow. It cracks. Silicone cures to a permanently flexible elastomer. It moves with the steel regardless of the loading applied.
The Application: SI-COAT 579 CM on the Hopper Exterior
SI-COAT 579 CM in Ansi Grey was applied to the hopper exterior over 18 to 20 June 2024. Surface preparation used hand tool and power tool cleaning to remove loose corrosion, cracked epoxy and surface contamination. No abrasive blasting was required. No primer was applied before the silicone coating. The single-component moisture-cure silicone applied directly onto the prepared steel surface.
The application required no hot work, no specialist blasting equipment and no extended facility shutdown. The port operation continued normally throughout the application period.
Three Months After Coating: No Cracking, No Corrosion
At the three-month inspection on 27 September 2024, SI-COAT 579 CM showed no cracking, no blistering and no corrosion on the treated hopper exterior. The coating had maintained its integrity through three months of continuous bulk material loading operations — the same impact loading conditions that had caused the previous epoxy coating to crack and fail.
The result confirmed the core performance claim. A permanently flexible silicone coating absorbs the impact transmission that cracks rigid epoxy films, maintaining the moisture barrier that prevents corrosion from initiating beneath the coating surface.
Why Epoxy Fails and Silicone Succeeds on Impact-Loaded Steel
The difference between epoxy and silicone performance on hoppers and other impact-loaded steel structures comes down to one material property — elongation at break.
Epoxy coatings cure to a rigid film with low elongation. When impact forces transmit through the steel wall, the coating cannot deform. Stress concentrates at surface irregularities, weld lines and edges. Cracks initiate and propagate through the rigid film. In a marine coastal environment like Durban Harbour, those cracks immediately become moisture ingress pathways and corrosion accelerates beneath the film.
SI-COAT 579 CM is a single-component, moisture-cure RTV silicone corrosion maintenance coating manufactured by CSL Silicones and available exclusively across Sub-Saharan Africa through <a href=”https://www.tssupplies.co.za/si-coat-579-cm-corrosion-maintenance/”>Technical Solutions Supplies</a>. Its independently tested elongation at break exceeds 180%. When impact forces transmit through the steel, the silicone film deforms elastically and recovers. No cracks form. The moisture barrier remains intact. Corrosion cannot initiate beneath an intact coating.
SI-COAT 579 CM also resists the marine environment directly. Its silicone chemistry does not hydrolyse in salt air. It does not chalk, yellow or embrittle under the intense UV radiation of KwaZulu-Natal’s coastal environment. It passed 3,000 hours of salt fog resistance testing per ASTM B117 with no scribe failure — independent confirmation of its performance in exactly the conditions Durban Harbour presents.
For more on how SI-COAT 579 CM performs across corrosion environments in Sub-Saharan Africa, visit our corrosion protection articles: https://www.tssupplies.co.za/category/corrosion-protection/
Epoxy vs Silicone for Hopper Corrosion Coating: Head to Head
| Epoxy Coating | SI-COAT 579 CM (Silicone) | |
|---|---|---|
| Modulus | High — rigid film | Low — permanently flexible elastomer |
| Elongation at break | Low | 180%+ |
| Impact resistance | Cracks under repeated impact transmission | Deforms elastically, recovers without cracking |
| UV stability | Chalks and degrades under UV | Permanently stable, no topcoat required |
| Salt fog resistance | Variable — degrades in marine environments | 3,000 hours ASTM B117, no scribe failure |
| Surface preparation | Requires abrasive blasting for adhesion | Hand or power tool cleaning only |
| Primer required | Yes | No |
| Application | Multi-coat system | Single coat, no primer |
| Service life in coastal environments | 5–8 years before recoating | 20+ years under field conditions |
| Hot work required | Often yes for surface preparation | No |
Key Takeaways from the Durban Harbour Trial
Rigid coatings fail on impact-loaded steel not because of poor adhesion but because their chemistry cannot accommodate the mechanical demands of the environment. Specifying a coating for its corrosion resistance alone, without considering the dynamic loading the substrate experiences, produces predictable failure.
Silicone’s permanent elasticity is not a secondary benefit — it is the primary performance differentiator on hoppers, bulk handling equipment and any steel structure subject to continuous impact or vibration. The Durban Harbour trial confirms that SI-COAT 579 CM maintains coating integrity under the impact loading conditions that crack epoxy films.
A single application requiring no abrasive blasting, no primer and no hot work delivers both the flexibility and the marine corrosion resistance that port and bulk handling infrastructure demands.
Frequently Asked Questions
Why does epoxy crack on the outside of a hopper when impact occurs on the inside?
Impact from bulk material loading on the inside of a hopper transmits shock and vibration forces through the steel wall. Epoxy is a rigid, high-modulus coating that cannot deform under these forces. Stress concentrates in the coating film at surface irregularities and weld lines, causing cracks to initiate and propagate through the epoxy from the outside surface. Once cracked, the coating no longer provides a moisture barrier and corrosion begins at the exposed steel beneath.
What makes silicone coating better than epoxy for hopper corrosion protection?
Silicone coatings cure to a permanently flexible elastomer rather than a rigid film. When impact forces transmit through the steel wall, the silicone deforms elastically and recovers without cracking. This maintains the moisture barrier that prevents corrosion from initiating beneath the coating surface. SI-COAT 579 CM achieves 180%+ elongation at break, compared to the low elongation of rigid epoxy systems, making it specifically suited to the mechanical demands of hopper and bulk handling applications.
Does SI-COAT 579 CM require abrasive blasting before application on a hopper?
No. SI-COAT 579 CM requires hand tool or power tool cleaning to remove loose rust, cracked coating and surface contamination. Abrasive blasting is not required. This significantly reduces preparation cost, eliminates the need for blast containment at operational port facilities, and allows application without extended shutdown of port operations.
How does SI-COAT 579 CM perform in Durban Harbour’s marine environment?
SI-COAT 579 CM passed 3,000 hours of salt fog resistance testing per ASTM B117 with no scribe failure. Its silicone chemistry does not hydrolyse in salt air and does not degrade under UV radiation. These properties make it specifically suited to the high-humidity, high-salt-aerosol, high-UV conditions of KwaZulu-Natal’s coastal port environment, where conventional epoxy and polyurethane systems have significantly reduced service lives.
Can SI-COAT 579 CM be applied over existing cracked epoxy?
Areas of cracked, loose or poorly adhering epoxy must be removed by hand tool or power tool cleaning before application. Firmly adhered existing coating in sound condition can remain. SI-COAT 579 CM bonds directly to the prepared substrate, including over sound existing coatings that pass an adhesion test of 4A or 4B per ASTM D3359.
Where is SI-COAT 579 CM available for port and bulk handling applications in Southern Africa?
Technical Solutions Supplies is the exclusive Sub-Saharan Africa distributor for CSL Silicones. SI-COAT 579 CM is available across South Africa and the broader Sub-Saharan region. Contact TSS directly for pricing, technical data and application support for port, mining and bulk handling infrastructure.
To discuss your hopper coating requirements, contact us: https://www.tssupplies.co.za/contact-us/
For technical questions and product specifications, visit our FAQ page: https://www.tssupplies.co.za/faq/
For more corrosion protection articles and case studies, visit: https://www.tssupplies.co.za/category/corrosion-protection/
Proud distributors of CSL Silicones.