From 1 January 2020, ocean-going vessels will be required to burn marine fuel with a maximum sulphur content of 0.5 per cent, down from the current cap of 3.5 per cent, under the International Maritime Organisation (IMO) regulation.

To meet this requirement, ship owners and operators will either retrofit Advanced Air Quality Systems - known in the industry as exhaust gas cleaning systems or scrubbers - on existing ships, or use expensive and unstable low sulphur fuels.

As owners contemplate which scrubber system to use (e.g. open, closed, hybrid), shipyards are also building up installation expertise. However, one often overlooked aspect of installation is paint selection according to Ismail Tan, global marketing manager for newbuilds at Jotun Marine Coatings.

“Due to the acidic environment within a scrubber system, most of the parts associated with scrubbers are made from GRP and stainless steel amongst other corrosion resistant material; but holding tanks and outlet nozzles are areas which are usually made of less corrosion-resistant material, such as mild or lower-grade stainless steel. These areas will require protective coatings to prevent corrosion, and the wrong products will yield high labour costs, materials and downtime costs for repairs,” points out Tan.

“It is also recommended that even scrubber internals, which are typically made of acid resistant stainless steel, should be coated with acid resistant protective coatings to ensure the scrubber can last a lifetime. After spending between $1 - 8 million (depending on size) on retrofitting costs, owners would hope not to have to deal with breakdowns due to improper paint usage,” Tan adds.

Not straightforward

Choosing the coating product is not straightforward as there is no blanket solution for every situation adds senior engineer Magne Aas, who works in Jotun’s Corporate Technical Support Department, TSS, Performance Coatings. “There are many variations in scrubber technology and operating settings, and therefore significant differences in conditions the materials will be exposed to. We can also expect local variations in the conditions (e.g. pH) within the scrubber system due to the actual temperature ranges and flow variations and then potential condensation of sulphuric acid.”

Meanwhile, switching to low sulphur fuel has its own issues and costs when it comes to emptying and cleaning the current high sulphur fuel tanks. As reported by Seatrade recently, the issues are both technical and commercial, notably for ship operators with ships deployed on time or trip charters in which bunkers are procured and paid for by charterers. “

Suppliers should, at minimum, guarantee the system for a period between 3 to 5 years to be in line with a vessel’s drydocking schedule, be it for a retrofit vessel or a newbuild, as it allows for repairs to be made during the drydocking period instead of calling a vessel out to repair and incurring further downtime. The protective coating performance, however, should last well beyond the guaranteed period. Costs for repairs of the particular damaged area is small but costs of getting to that particular area to repair it is extremely high,” adds Tan.

Protective scrubber-proof coating solution

The solution is a protective coating capable of withstanding this acidic environment protecting scrubber internals. In addition, corrosion protection for the hull around the outlet nozzle must be adapted to the composition of the discharged scrubber water, design of the hull and the flow simulations, points out Aas.

Drawing from experience protecting huge land-based scrubbers at power plants, Jotun has customised its products for marine SOx scrubbers. Chemflake Special, a high-performing Vinyl Ester Glass flakes coating, is capable of withstanding a scrubber’s acidic environment. Meanwhile, Tankguard Special Ultra, a Novolac Phenolic Epoxy coating, is originally and still used in chemical carrier cargo tanks due to high chemical resistance.

Both these products are existing products that well known in their respective industries and have been developed further for marine SOx scrubbers.

Concrete benefits include steel preservation by using a protective coating that ensures scrubber systems remain protected and effective at cutting SOx emissions without incurring increased fuel costs. Also, the protective coatings are durable, thereby reducing repair and maintenance needs in scrubber systems, pipes and tanks.

With a healthy, global supply network, Jotun can serve the potentially huge volume of vessels coming in for expensive retrofitting. In the future, this demand will ease and become part of a newbuilding requirement.

Jotun is one of only two companies in the market actively working with owners and shipyards to develop a workable solution for scrubbers, and have successfully secured 80 vessels thus far, making it one of the leading solution providers for scrubber systems.

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The IMO’s global sulphur limit for marine fuels comes into force January 2020. To meet the regulation, shipowners need to switch to cleaner marine fuels. Alternatively, they can carry on burning fuel oil and fit scrubbers to achieve emissions complaint with the standards set by IMO 2020 – and subject to the approval of the ship’s flag state.