Offshore oil and gas operators have to cope with wildly fluctuating economic conditions, so the last thing they need to worry about is corrosion problems. Demands for 20-year corrosion protection, with the minimum amount of maintenance, are now common in the upstream offshore world.
The harshest environments in the world have forced coating manufacturers to push the envelope, while inspection methods are also advancing rapidly. The most critical area on offshore assets such as FPSO’s (Floating Production, Storage and Offloading units), drilling units, fixed platforms and semi-submersibles is the splash zone, where the elements needed for fast corrosion are in plentiful supply: air, water, salts, UV, ice, and mechanical damage. Access for inspection and maintenance is also difficult and expensive. Traditional epoxies struggle to cope in these conditions, so specialist coatings are becoming more common.
Glass flakes
“Customers are increasingly looking for new approaches to address the challenges of longevity, aggressive production schedules, cost reductions and minimising their environmental footprint in the offshore oil & gas sector,” explains Simon Daly, Oil, Gas & Thermal Power Segment Manager, Hempel A/S. “This has led to more ultra-high solids glass flake epoxies being used in coatings for the oil and gas sector. Traditionally, these were being used for internal tank linings, but increasingly these products are being used in the offshore arena thanks to their high-performance resistance to corrosion, chemicals and high temperatures.
“Put simply, customers want a coating which will perform to the highest standard and prolong the life of an asset and reduce maintenance costs. Offshore installations are exposed to some of the harshest conditions and getting the coating right from the outset is vital to protecting it for its entire service life. Longer service life for example, in offshore assets also results in not having to put maintenance painting personnel in potentially hazardous situations. Additionally, customers want coatings that are easy to apply and fast curing to reduce application and maintenance costs even further.”
Daly continues: “At Hempel, we strive to assist our customers to prolong the life of their assets and reduce the need for on-station maintenance, through the provision of industry leading and trusted coating solutions that protect our customers’ assets and add value to their businesses. With over 100 years’ experience in specialty coatings, we play a vital role in safeguarding these valuable assets; helping to reduce maintenance costs and keeping them looking good for longer.”
Hempel’s Hempadur Multi-Strength 35840 and 35842 are 98 per cent solids epoxy glass flake coatings specifically designed for splash zone protection. They are formulated with reactive diluents rather than conventional solvents, which allow the application characteristics of a solvent based product whilst reducing VOC, worker exposure to solvents and the risk of solvent entrapment which may ultimately impact the performance of the final coating.
“Increasingly, as higher DFT’s are being used, often in aggressive production cycles with little time between coats, it makes sense to use a product where the waiting time for the solvent to be released from the paint film is minimised,” explains Daly. “The addition of solvents to products to reduce viscosity, thus allowing continued application in colder weather, can further exacerbate the problem. Physical property development occurs much quicker when compared to lower solids epoxy systems. This allows for quicker handling of coated items. Additionally, the higher volume solids of the products result in less paint being needed for the same surface area, meaning added benefits in application time, wastage and transport and storage costs.
“Hempadur Multi-Strength 35840 and 35842 replace most of the conventional solvents with reactive diluents. These are low viscosity molecules that allow the application characteristics of the product to be maintained. As these materials react fully with the polymer background of the product, there is a reduced possibility that the solvent will be retained within the finished coating film.”
Rehabilitation
The Pertamina RU V refinery on the coast of Balikpapan, Indonesia, is subject to a continual harsh environment and potential corrosion. Both weather conditions and seawater exposure of the refinery’s fenders mean that when maintenance is needed, painting crews have to work quickly in tight spaces to remove the old coating and corrosion and begin repainting immediately. The difficulty of repair demands that coatings are highly durable.
In a recent rehabilitation programme, PPG’s Sigmashield 880 was selected for abrasion, corrosion and seawater resistance as well as fast-drying time, and high-film thickness in a single coat. A single coat was applied to a thickness of 500 microns (20 mils) by airless spray, achieving the necessary thickness in a single coat despite the elevated air temperature of 31°C.
Tests showed the coating withstood the splash and immersion effects of the Makassar Strait’s salty waters, and showed substantial crack and sag resistance even at high-film thickness. It was also able to withstand tidal effects, reducing the maintenance required on the structure and remaining in good condition even after 15 months of service.
The same coating system was also selected for the refinery’s jetty, where rapid drying time was key. The coating was subjected to immersion within 30 minutes after application due to the tide, but continued to cure without adverse effect. PPG point out that although the Sigmashield 880 coating is not reinforced, it still achieved the vital abrasion resistance, and its improved cathodic disbondment protection provided enhanced corrosion resistance.
Phosphate surface
Meantime, a more radical coating solution for similar conditions has also been gaining approval. Merrick Alpert, President of EonCoat, LLC, says owners of offshore assets want to reduce the amount they have been paying for fabric maintenance: “They want to apply corrosion protection on their new build assets that will last for the production life of the asset. And for existing offshore assets, they want to replace the three coat system they have in use and then not revisit it again.”
EonCoat is a spray applied industrial coating that prevents rust on carbon steel. The coating reacts with the surface of the steel it comes in contact with, forming an amorphous magnesium iron phosphate layer. This true alloy – it is chemically bonded to the steel – becomes the first line of defence against corrosion. On top of that, a white ceramic layer forms over the alloy as a second line of defence, whilst also providing a reservoir of phosphate to continuously maintain the alloy layer.
“We have seen both new construction and maintenance work using EonCoat in order to avoid the traditional blast-paint-corrode cycle,” explains Alpert. “The cost of maintenance on a rig can be up to 100 times as expensive as land-based maintenance because crews and supplies often have to be helicoptered out to the site, so when coatings fail it costs the asset owner enormous amounts of money.
“Currently, EonCoat is in use on the platforms of Total (North Sea), Nexen/CNOOC (North Sea), Shell (Gulf of Mexico) and BHP (Trinidad and Gulf of Mexico).”
Scratch resistant
Abrasion tests conducted on a Taber machine, using an abrasive wheel rotating against a coated panel, shows the EonCoat surface does not scratch easily. The number of cycles required to create a thousandth of an inch wear for most polymer paints is about 75 cycles, and for an ordinary epoxy about 125-250 cycles. Over 1200 cycles were needed to get the same amount of wear in EonCoat.
Alpert says there are three options for repairs of older systems: “Large Scale Repair (such as the replacement of a section of a platform that previously had a traditional three coat system) is done by a full size plural pump, with EonCoat applied after the old coating has been blasted off. Mid Scale Repairs would use a cartridge spray unit, and Small Scale (Spot) Repairs are done with a plural component applicator, similar to a caulk gun. This is the only time that EonCoat is brush applied. As there is an unlimited ‘recoat window’ with EonCoat, areas that have suffered mechanical damage can be sprayed at a later date. It can be days, weeks, months or years later.
“The problem with glass flake, as with any traditional coating, is that it is a barrier coating. The steel remains reactive beneath it, so that over time it is guaranteed to lead to corrosion. By alloying the steel so that it is passivated and does not corrode, EonCoat approaches corrosion prevention in a completely different way.”