On the Line: A revolution in ship repair AreA review: Middle Eastern yards buck the trend

wOrLdwide: A strong rise in offshore works

Magazine September 2013

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Extreme weather conditions, dissolved oxygen, salt-water abrasion and corrosion, ultraviolet exposure, mechanical impact from debris and

damage by marine life combine to present multiple opportunities for corrosion. as protection may have to last for 25 years, the demands are at the limits of technology.

repairing a failing underwater coating onsite is, of course, impractical. While some rigs, such as semi-submersibles, are moveable, drydocking a working platform can easily cost more than $1m day in lost production alone, so operators need a coating to last as long as possible. since the lives of crew also depend on corrosion protection, regulatory standards are correspondingly strict.

the oil and gas industry have generally asked coatings suppliers to provide 15 year lifecycles, and in some cases up to 25 years. But expectations of working life for rigs are growing, and 40-year corrosion protection is now being seriously discussed.

thE chAllEnGEdifferent types of vessel and installation are involved in the business of extracting oil and gas – typically a drilling rig will bore down to create a new well, then a production platform or fpso (floating production, storage and offloading) unit will move in to harvest the product. oil or gas is transferred, either via pipeline or to floating storage units or tenders.

unlike regular shipping, offshore installations are not greatly concerned with increased drag due to marine growth or fouling. however corrosion inspections need to be made regularly if drydocking is to be avoided, where this is accepted within the vessel’s class. cleanability is needed in these cases, so hard coatings are the norm. cleaning might also be required before moving a rig, to reduce drag.

Facing the elemental

challengeprotecting offshore oiL and gas pLatforMs is one of the toughest chaLLenges facing the coatings industry expLains Mike garside.

28 In focus

drydock 2013 29

clEAn hullsstationary vessels are open invitations to both micro and macro fouling, especially considering that conventional biocidal antifoulants require flowing water to work. these factors allow stationary vessels to accumulate fouling to almost hard-to-believe levels in a relatively short time.

Marine fouling accumulates quickly, even in cold waters. in warm waters such as the gulf of Mexico it grows very rapidly: more than 300mm (12 inches) of growth can build up between inspections. it has to be removed before underwater weld seams and surfaces can be checked, and the heavy brushing required

designed to permit easy removal of fouling, although the usual lifecycle of anti-fouling coatings would only offer 2 to 5 year effectiveness. others suggest vinyl ester or polyester resin base reinforced with glass platelets will provide exceptional toughness and a long lifecycle, with sufficient durability to permit cleaning as often as necessary.

thermal spray aluminium (tsa) coatings have been used on some offshore structures but may not be suitable for all areas: in immersion areas the tsa will act as an anode and sacrifice itself to protect exposed steel. even at thick builds of 10-15 mils, the sacrificial action will quickly consume the tsa coatings, leaving bare steel.

cupronickel or copper-nickel has been used in some cases to protect the legs of offshore platforms, as in the Morecambe gas field. it is highly resistant to corrosion in seawater, because its electrode potential is adjusted to be neutral with regard to seawater.

stAndArdsthe norsok standards were developed by norwegian petroleum industry for offshore installations. norsok M-501 specifically deals with anticorrosive coating systems and the processes related to their application. it covers the

selection of coating materials and defines the requirements of surface preparation, application procedures and inspection for protective coatings to be applied during the construction and installation of offshore structures and associated facilities.

norsok M-501 identifies coating systems for nine main areas, some of which need to be pre-qualified through a long-term test program carried out by an independent laboratory. these tests are covered by iso 20340 which includes chemical screening and several performance tests. for its ageing test, the fully cured coating system is scribed horizontally down to the bare metal and the system is exposed to a cyclic test with a total exposure time of 4,200 hours. a seawater immersion test assesses panels with a scratched coating system after 4,200 hours of exposure in synthetic seawater at 40°c. a cathodic disbonding test measures the maximum disbonding after six months exposure time. the complete test programme typically takes about nine months.

the standard also stipulates that all personnel involved in the application and inspections prove their qualification. painters need to present craft certificates or pass tests on-site, and paint inspectors

must be certified according to frosio or nace.

norsok M-501 has become a universally recognised standard that meets the most stringent requirements for corrosion protection.

coAtInG fAIlurEsWhere coating failures have occurred, it is most often blamed on application problems – adherence to standards and manufacturers specifications are particularly important. Beam edges are a common concern, if beams have not been radiused or stripe coats not applied. the presence of much pipework also brings problems, with corrosion often appearing at points such as where buckles on stainless steel banding have punctured the coating, or id tags and float level indicators prevent coating, or at field welds. there is also a high chance of mechanical abrasion or damage from floating debris on platforms.

as with all marine coatings; if paint is applied in high humidity or extreme temperatures, or if pressure to complete the job overrides best practice, then problems are more likely to occur.

as lifecycle demands increase, blasting to sa3 (“all millscale, rust etc. removed and the surface has a uniform white metal appearance with no shading,

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32 In focus

The expectations of working life for rigs are growing, and 40-year corrosion protection is now being seriously discussed.

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stripes, spots of discoloration”) rather than the usual sa2.5 is now being stipulated in some coatings contracts.

ExtEndInG lIfEtImEsshell uk and nederlandse aardolie Maatschappij Bv own and operate 56 offshore oil and gas installations in the southern sector of the north sea. Many of the platforms have exceeded their original design lifetime, with some having been in service for almost 40 years. in a major refurbishment project international paint specified a coating system using the high build, surface tolerant and user-friendly protective coating interzone® 954. for the uk platforms, 45,000 litres (9,899 gallons) of interzone 954 (at 350μm or 13.8mil dft) has been used so far to protect over 100,000 m2 of topsides and splash zones, including handrails and ladders.

rAIsInG thE GAmEtoby stein, upstream oil and gas Market Manager for international paint, says that 40-year coating life expectations for new construction schemes are placing increasing demands on coating suppliers:

“it means we don’t just consider the minimum test data requirements that are mandatory. consideration for full life in-service performance is also taken into account. owners want proof of a coating’s reliability. thicker is not always better and we have to strike a balance. We also have to take into account the surface preparation methods used in the yard and tolerance to the other construction processes which may damage the coating during fabrication. offshore structures can be quite complex and yards have bespoke build processes. the coating must suit the application and yard conditions as well as offer long term corrosion performance once in service. it takes a lot of experience to recognise this and understand which coatings are suitable. this goes for all areas of an offshore project, whether splash zone, submerged, atmospheric or high-heat areas.”

“the offshore industry has settled on sa2.5 steel cleanliness and a surface profile of 50-75 microns. it is also important to remember that many owners will want the fabrication yard’s shop-primer completely removed as they see it as a point of potential weakness for long-life schemes. this is not so in the commercial maritime industry as vessels can be more easily repaired in dry-docks. a shop-primer is a thin layer, prefabrication zinc primer (typically 20 μm (0.8 mils thick), which protects the steel during the fabrication process prior to the major fabrication beginning. for long term performance, getting the correct surface profile and acceptable salt contamination level for a coating system is critical.”

international paint generally recommends its interzone 1000 for the splash zone and intershield® 300 or interzone 954 for submerged areas for new construction. in addition to meeting the norsok M-501 standard, stein continues “Many oil companies have their own internal specifications to which products like these are approved. interzone 1000 and intershield® 300 do not require specific topcoats for corrosion protection. Where fouling build-up presents a challenge to underwater inspections easy-clean fluoropolymer foul-release coatings are currently used in the offshore market, such as international paint’s intersleek® range. Major oil companies such as shell, Bp, inpex and chevron select intersleek® to allow for easy inspection of the steel integrity on their floating structures and reduce the translocation of invasive species into sensitive ecosystems. demand for intersleek on floating production units has risen significantly since its first major application on the frade fpso in 2007. it has since been used on a range of projects including Chevron’s Jack St Malo semisubmersible production platform and has been selected for the Shell Prelude fLng.

AltErnAtIvE coAtInGs Jotun’s usual recommendation for offshore platforms is Baltoflake, a glassflake

reinforced polyester coating designed for protection in splash zones and immersed areas of offshore installations. Baltoflake was developed for resistance to abrasion, water and chemicals, and combines specially formulated polyesters with a glass flake reinforcement. due to the long service intervals Jotun do not usually recommend anti-fouling for these applications.

hempel’s range of coatings includes several technologies – normal recommendations for a platform would be hempadur Multi-strength 35460, a solvent free, two component epoxy coating. in the splash zone, with submerged areas covered by hempadur Multi-strength 45703, a self-priming, two-component, highbuild, aluminium pigmented pure epoxy paint which cures to an abrasion and corrosion resistant coating.

epigrip c402v2, a zinc phosphate primer/buildcoat for splash zone areas, and epigrip M922 (glass flake epoxy transgard tg123) is sherwin Williams’ suggestion for submerged areas.

the zinc phosphate coat is a high build 2-pack epoxy zinc phosphate primer/buildcoat, applied to a dry film thickness of 100 microns, and requires a top coat only for decorative purposes.

the glass epoxy coat is a high solids 2-pack epoxy pigmented with micronised glass flake and anti-corrosives, designed for use with blast cleaned steel and cathodically protected steel. this is applied to a dft of 400 microns.

Marine fouling grows rapidly in warmer waters, presenting addition demands on coatings.

“We are authorised by class to drydock the Odyssey every 15 years,” explains Jan. “the platform has propulsion systems that must be inspected every five years, but we have designed special cofferdams so that the rudders and propulsion systems can be inspected without drydocking the vessel.”

But the biocidal antifouling coating system which was used on the hull until last year did not provide the necessary anticorrosive protection, as it was not designed to last even ten years, let alone 15.

“this vessel travels slowly,” says Bakke. “We all know first of all that antifouling on this type of slow moving vessel doesn’t have the ablative properties needed to prevent fouling, so whether you have biocidal antifouling or a hard coating you will get sea growth.” With the soft, antifouling coating system, the biofouling is harder to remove and it will eventually penetrate the coating.

there were problems connected with cleaning the biocidal af coating previously in use. “When you start cleaning the hull on an antifouling system then you set the clock for docking,” explains

Jan. “you have to continue cleaning. that’s where the turn point is on the economy of it. and i did quite some study on it in my younger days. typically it’s 9 - 12 months from the point where you start cleaning to the point where you have to drydock to repair/replenish the antifouling coating. if you start cleaning earlier than 9 - 12 months before the point where you are due to drydock, you’re on a downhill race.”

as oil exploration continues at depths which would have been thought impossible until a few years ago, the cost of rigs and technology increases. With those increased costs the length of time a rig needs to stay in service also increases. the coast of Brazil is now generating great interest, but there in the santos Basin the depth of drilling required is likely to be over 3 miles (7,000 feet of water, 6,600 feet of thick salt, and 4,000 feet of rock). arctic drillships have been developed that can drill as deep as 11km (7 miles) in the sea. keeping such rigs free of corrosion and excess marine growth for extended periods is at the edge of coating technology.

38 In focus

“Antifouling on this type of slow moving vessel doesn’t have the ablative properties needed to prevent fouling

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