Protection in extreme environments

UK-based specialist polymer coatings development and applications company Capps Vessgard has reported ten years of service life protecting the bulkheads of the first self-unloader bulk carrier vessels to apply the product. The owners have achieved the complete elimination of steel renewal requirements during this period on all applied areas.

The advanced high film build polymeric encapsulation system is manufactured and applied by CAPPS International, with application controlled by proprietary equipment systems. The product is spray applied to a dry film thickness (DFT) of up to 5mm in one application, with the first vessels applying 2mm DFT to the highest wear zones of the cargo hold bulkheads.

The 1991-built 96,722 dwt bulk carrier Yeoman Bridge is one of the largest self-unloaders in the world. The vessel is on a continuous transport schedule moving granite from the owner’s quarry in Glensanda, Scotland to various European ports. It was the first vessel to specify a full scale application of CAPPS Vessgard.

Prior to application, the aggressive nature of the granite cargo was the first problem faced by the owners when maintaining their cargo hold internal bulkheads. The other major issue was the level of throughput created by the vessel’s short sea transport schedule that provides for 45 cargoes each year. This corresponds to a total deadweight of approximately 3.8 million tonnes every 12 months.

With this level of throughput the mechanical wear that each bulkhead must endure with intense abrasion, pressure, impact damage and corrosion creates one of the most aggressive and abrasive internal cargo hold environments in the bulk carrier industry. Conventional epoxy coatings were not performing for the owners, creating a vicious circle of premature coating failure and then aggressive bulkhead steel damage in service.

With the significant threat of substantial corrosion, and class-imposed steel renewals looming in 2005, a more permanent method of protection was sought. The alternative was major steel renewals at considerable cost and time. The owners were aiming for a target service life of 40 years, further necessitating a long-term solution.

During the vessel’s 2005 dry dock at Lisnave in Portugal, all transverse corrugated bulkheads were applied with a CAPPS Vessgard to 2mm and 1mm DFT. The lower 7 metres of each bulkhead were applied to 2mm DFT and then the next 4 metres applied to 1mm.

After 28 months the vessel had transported 7.2 million tonnes of granite aggregate and the system was showing no major signs of wear. The heavily pitted steel remained fully encapsulated by the high film build system. The lower sections of the bulkheads were clearly taking the heaviest wear in line with the vessel’s discharging characteristics but the encapsulation was holding firm.

At her next dry docking in January 2008 the decision was therefore made to progress further. CAPPS Vessgard was applied to the flat longitudinal bulkheads in all cargo holds and the flat forward bulkhead in cargo hold 1. This made Yeoman Bridge the first vessel in the world to have complete CAPPS Vessgard protection on all of her cargo hold internal bulkheads. Since then the vessel has continued to be CAPPS International’s flagship of performance reference for the bulk carrier industry.

Over ten years of performance the company reports that there has not been one requirement for steel renewals – a major achievement considering the areas of steel beneath the encapsulation running close to substantial corrosion margins. The owners have also eliminated the considerable costs of scaffold staging, grit blasting and full reapplication of epoxy systems to all cargo holds at every dry dock over this period.

The ability to reapply the product to localised high wear areas has contributed to this longevity and economy of scale, with the system being maintained by spray application to specific high wear zones on the lower sections of the transverse corrugated bulkheads in 2010 and 2015. The first 10 years indicates that the coating will indeed provide the 40 years of service life that the owner expects, at a much lower cost and time investment than the alternative use of epoxy systems and major steel renewals.

Tim Cole, managing director, CAPPS International, said: “The success of CAPPS Vessgard after 10 years in the most aggressive bulk carrier cargo hold environment in the world is powerful promotional evidence for new owner clients. We now have the solid evidence required to expand further into the worldwide self-unloader bulk carrier market.”

Cole reports that the next progression for the company is into conventional capesize iron ore bulk carriers. “We are targeting major capesize fleet owners of the size that have an open eye to a good long-term investment, even in a challenging market. We have active enquiries currently progressing with keen interest being shown in the performance of our unique product and application process.”