Feature: Tiny metal islands

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Offshore rig operators are under pressure. With low oil prices, new rigs ordered during the boom years are sitting idle. Existing assets are being kept out as long as possible, so more on-site maintenance is needed. But on-site coating repairs to key sections are difficult and expensive. Repairing a failing coating is hugely more expensive than the cost of coating when a rig is being built.

Owners now demand coatings that will last for at least 20 years. Increasingly 25, 30 or even 35-year lifespans are being specified. Most have developed their own policies, but annual inspections are usual, with some conducting their own, some sticking to predetermined schedules, and some relying on maintenance contractors to guarantee integrity.

Paint manufacturers meantime are responding to the needs of their market with ever more durable coatings.

Save a penny, spend a pound

Lasse Isaksen, Jotun’s Global Concept Director for Offshore says that while the new-build market has been slow since the crude oil prices dropped in mid-2014, there has been a corresponding requirement to increase the life of existing offshore assets. However due to the current economic climate the industry is looking at ways to extend intervals for fabric maintenance work, in an attempt to balance books. Operators are under financial pressure and are forced to reduce cost.

“From our viewpoint we can tell owners that the square metre cost of painting on location is about 10 to 20 times the cost compared to performing the work in a yard environment– so short term cost saving by cheaper coatings with a lower performance will not save money in the long run. In fact the cost of the coating material only makes up a small portion of the maintenance cost. Surface preparation and scaffolding are by far the largest cost drivers.

“Very often due to the absence of specifications, procedures, and overall philosophy from the operators, fabric maintenance contractors are left to provide recommendation on paint systems. In a very competitive market situation, this will not necessarily act as an incentive to promote solutions that will provide the longest maintenance intervals and best return on investment.”

Maintenance warranties

Some operators specify the use of NORSOK approved products/systems in order to safeguard a minimum level of quality. However the NORSOK and other standards such as the ISO 20340 focus on new construction, and thus products are designed for application in the yard, not re-coating installations in an offshore environment. Re-coating on location has to deal with issues such as elevated salt levels, brush/roller application, and risk of low film thicknesses as well as surface preparation challenges.

Lasse continues: ”The lack of international standards and a common approach towards offshore maintenance has resulted in a situation where the operators risk financial suffering, in the form of elevated fabric maintenance cost and increased down time.”

Contractors are also squeezed by the demands for longevity. The warranty period typically required from fabric maintenance contractors used to be between 1 to 3 years, but now warranty periods for up to 5 years on maintenance are required in some cases.

Lasse says studies performed by operators on existing assets operating in similar conditions indicate that the use of zinc based coating systems above the waterline and on process modules significantly reduces the need for maintenance during the life of the asset in addition to increased uptime.
Glass-flake protection

Phillips Petroleum Norway have been happy with the experience of using longer-lasting coatings. A letter from the company says they started using the glass-flake Baltoflake system in 1980 on large deck areas, bridges and helidecks in the Ekofisk area, and that now glassflake polyester, with non skid additive, is specified for helidecks and all exterior decks and walkways.

They also use Baltoflake for maintenance purposes on deck legs, and structure from sea level to underside of cellar deck, and specify glass flake polyester for the splash-zone. Their letter says: “As part of our maintenance paint program we have already coated the sub-cellar deck area (the entire structure between sea-level and cellar deck) on 12 of a total of 24 steel platforms in the Greater Ekofisk Area with glass flake polyester coatings. For long term protection we have specified min. 1000 microns DFT applied in two coats. We have found glass flake polyester to be an extremely versatile product for many ‘niche areas’.”

Surface tolerance

Coating manufacturers aiming at the mid range of market requirements are working on more surface-tolerant products that are easier to maintain and apply.

Maintenance comprises about 90% brush and roller application in small areas. For fabric maintenance contractors this means fitting their work around the production priorities of the rig, and in practice they can find their work down-prioritised against production demands.

Operators typically want to blast as much as possible during maintenance. This brings its own problems for maintenance contractors as it means building a pressurized habitat to avoid the grit contaminating nearby machinery. All of the grit has to be collected and properly disposed of. Many of the older assets on continental shelves are now having their lifetimes extended by 20 years, so they have to be stripped back to bare steel.

Repair programme

Chemco, based near Edinburgh, say the high cost of grit blasting and grit disposal, as well as environmental controls, have forced the industry to look at alternative surface preparation methods and products that can be applied on damp/wet substrates.

In 2012, their Speciality Coatings division in Singapore were asked to provide a solution to refurbish a platform as the existing coating system had failed.

Due to the nature of offshore platforms, accessibility to the platforms’ hull and living quarter areas was difficult. Tropical weather and high humidity was also a factor. With a tight schedule and the rig still in operation, grit-blasting was impractical and Chemco determined that water-jetting was the only cost-effective preparation method.

A gondola system was used to access the ships hull, with rope access for areas that the gondola could not access. High pressure water jetting removed the existing failed coating and rust, as well as substantial sea growth and salt contamination. The company decided that one coat of wet & rust tolerant Epo-chem RL 500PF could be applied without concern for humidity or dew point, followed by one topcoat of Epo-chem RC 500GTC, significantly reducing the time needed for the repair.

Floating gas

The challenge is to keep an asset out of dry-dock for long periods, with the hull and tanks free from corrosion. While static rig owners do not have to worry about the fuel penalties associated with a fouled hull, the coatings still need to be cleanable in the water to reduce weight and for Underwater Inspection In Lieu of Drydocking (UWILD), which prevents very costly time out of production.

New types of installations however may need to move from time to time. Manuel Hof at Subsea Industries in Belgium says that Floating Liquified Natural Gas (FLNG) vessels are a growing sector. “FLNG operators are somewhat pioneers in the energy sector. Their particular requirements involve some flexibility to be able to move the large container vessels, but they need to have the same durability and coating lifetimes as rigs.

“Exmar selected our ultra-high durability product EcoLock for the Exmar Caribbean, their first FLNG vessel. They are now using the same product for their first Floating Storage and ReGasification vessel which is being built in China.

“The Ecolock coating will survive in any climate and is very well suited to being cleaned when necessary. Exmar may want to keep it on one station for years with an underwater cleaning every two or three years, but they can also clean very easily if they want to move it. The original planned location for the Caribbean was off the Colombian coast where there is a lot of fishing, so a completely environmentally safe coating was another requirement.”

The Ecolock system is a glass-flake coating, developed for extreme toughness from the company’s Ecospeed ship hull coating. It is designed to protect offshore vessels for decades, even in ice or other harsh conditions, and can be cleaned as often as needed.

Wind energy learning

Anders Voldsgaard Clausen is Group Power Generation Segment Manager at Hempel and deals with, among other areas, the wind turbine industry. He says the wind sector has for some years followed trends from offshore oil and gas in the search for longer asset lifetimes.
“20 to 25 years is now the common lifetime being demanded for offshore coatings. Wind power installations have learned from the longer experience of offshore oil and gas installations. The difference is that with wind turbines we have the monopole sunk into the sea bed and a transition piece which sits on top. In theory below the splash/tidal zone there should be no corrosion, as there is no oxygen present. However in practice we do see some corrosion particularly on the inside of the piles if not coated.

“We tend to recommend coating monopiles with the same types of treatments as used above the waterline but without the need of the yellow topcoat. Some owners are now looking at glass flake systems, as on oil and gas.

“Inspection of the inside of monopoles is very difficult after installation, as is repair of coatings, except near the top where the transition piece sits. So it makes good sense to give these areas a long-lasting protection and it needs to be done at new build.

“Most operators have their own rules and procedures for inspection and maintenance, or otherwise they rely on maintenance contractors to specify and guarantee the condition. But inspection once a year is most common.

“We try to make it as easy as possible for contractors to conduct repairs when they are needed. There will always be unavoidable mechanical damage, either occurring during installation or from inspection boats hitting the legs, so we have products designed for that. For example, we provide smaller tins for maintenance contractors to use, which can be carried by one man hanging off a rope. We have also reduced curing times so that paint can be applied when there is only a short time before the weather turns bad. It takes quite some time for the contractors to set up harnesses and the work area, so they have to be able to work quickly.”

Hempadur Multi-Strength 35460 is the company’s solvent-free protective coating designed for offshore wind turbine foundations. The coating offers a six-hour drying time. Along with previous versions, it has been used on more than 20 wind farms, including the 375 MW Walney Offshore Wind Farm in the Irish Sea. The repair version of the coating, Hempadur 3546b, is designed to give 1000µ thickness with just one coat.

Abrasion

Jake Ojeda, Offshore Segment Manager at PPG, says the industry is focused on enhanced performance and improved cost efficiency. His company recently released SIGMASHIELD 880, aimed to offer cost savings and superior abrasion resistance for specialist offshore applications. The coating gives tolerant surface preparation and extended service life with single-coat application. It can be rapidly immersed and continues to cure after seawater immersion, so is well suited for structures exposed to tidal movement and surges, and for offshore splash zones. Other applications include decks, walkways and topsides, helidecks, jackets and caissons.

The coating was used on the Congorep/Perenco offshore platform, part of an offshore development including more than 30 units located in the Emeraude Field, south of Pointe-Noire, Republic of Congo.

This production platform supports 13 wells that were projected to produce 2,500 barrels of oil per day but currently exceeds that target rate. Perenco operates three offshore fields in the Republic of Congo and has a gross production of 18,000 barrels of oil per day.

In addition to the effects of wave action, floating debris and the corrosive effects of the offshore drilling environment, Perenco’s PPN1 platform had suffered from a lack of past maintenance. There was significant corrosion and structural damage: platform surfaces were 80% rust covered and re-painting was needed urgently to stabilize the structure prior to more extensive repairs.

Surface preparation (by abrasive blasting to Sa 2.5) and painting took place over a two week period. A single coat of SIGMASHIELD 880 averaging 350 micron thickness (14 mm) was applied by airless spray and was subject to immersion in sea water after only 30 minutes due to the rising tide. The rapid drying and short time to immersion were key factors.

The application successfully stabilized the platform, enabling further repair and maintenance and achieved long term protection.

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