Flex­i­ble coat­ings help pro­tect marine struc­tures

DEMM Engineering & Manufacturing - - PRODUCT WATCH -

Both abra­sive and cor­ro­sive, the marine en­vi­ron­ment is un­for­giv­ing of mar­itime struc­tures such as off­shore plat­forms and rigs, and ocean- go­ing ves­sels – all of which are ma­jor in­vest­ments for the com­pa­nies op­er­at­ing them. All ac­tiv­i­ties in a marine en­vi­ron­ment are im­pacted by cor­ro­sion; the preven­tion, con­trol and re­me­di­a­tion of which costs in­dus­try bil­lions of dol­lars each year.

One way to min­imise and mit­i­gate the ef­fect of some types of cor­ro­sion is through the use of flex­i­ble sur­face coat­ings that are re­sis­tant to chem­i­cal at­tack from petroleum prod­ucts and salts. Ac­cord­ing to De­nis Baker, Spe­cial Projects En­gi­neer at Gold Coast- based Rhino Lin­ings Aus­trala­sia (RLA), “A cor­ro­sion bar­rier has to have dura­bil­ity and flex­i­bil­ity in ad­di­tion to be­ing im­per­me­able to the wide range of agents that af­fect mar­itime struc­tures.”

An off­shore struc­ture is also harsh on sur­face coat­ings, both in terms of how they wear and also how they are ap­plied. Some of the ar­eas most af­fected are the decks, su­per­struc­ture, bal­last tanks and an­chor or chain wells. These are both ex­posed to salt and other chem­i­cal agents as well as to abra­sion as peo­ple and equip­ment move about. To en­hance safety for per­son­nel mov­ing around an off­shore struc­ture or ves­sel, spray ap­plied sur­face coat­ings with anti-slip prop­er­ties can eas­ily be ap­plied to decks to pro­vide safe walk­ways.

Ac­cord­ing to Baker, it is pos­si­ble to min­imise some of the ef­fects of drilling op­er­a­tions by ap­ply­ing two par­tic­u­lar Rhino Lin­ings coat­ings that have been de­vel­oped for mar­itime struc­tures used in the oil and gas in­dus­try.

On an oil pro­duc­tion rig, the ar­eas where the 14 me­tre lengths of drill pipe are laid out be­fore be­ing dragged across the deck and pulled up for drilling op­er­a­tions are prone to a large amount of dam­age. Most sur­face coat­ings are quickly abraded away ex­pos­ing the bare metal to cor­ro­sion.

To pre­pare these work­ing ar­eas for treat­ment with the Rhino Lin­ings coat­ings, the plat­form deck has to be abra­sive blasted to clean off any ex­ist­ing coat­ings and also pro­file the sur­face for op­ti­mal ad­he­sion of the primer and pro­tec­tive coat­ing. Zinc-rich primers can then be ap­plied to the pre­pared metal sur­face, over which a pro­pri­etary Rhino Lin­ings primer is rapidly sprayed. Rhino 161 or 251 are good choices for this type of ap­pli­ca­tion be­cause they have no volatile or­ganic com­po­nent ( VOC) prop­er­ties and can be eas­ily and quickly ap­plied. For max­i­mum pro­tec­tion, Rhino Pure Polyurea (for ex­am­ple Ex­treme or PP1195) is then ap­plied over the primed area to a nom­i­nal thick­ness of 3000 mi­crons on the deck sur­face. This fi­nal coat­ing was cho­sen for its re­sis­tance to weather ex­tremes, ex­cel­lent flex­i­bil­ity and high im­pact strength. The abil­ity to walk on a Rhino Lin­ings sur­face in a mat­ter of min­utes means that a fa­cil­ity can be back on line sooner.

A ma­jor con­sid­er­a­tion in ap­ply­ing any sur­face treat­ment to a struc­ture is the re­quire­ment to min­imise down­time. Spray coat­ing en­ables quicker ap­pli­ca­tion and less dis­rup­tion to a client’s op­er­a­tions. “The beauty of our coat­ings is that they are rapid set­ting,” said Baker. “We can spray them on and they cure in as lit­tle as six sec­onds.” Un­like all other coat­ings, Pure Polyureas are not af­fected by am­bi­ent mois­ture or tem­per­a­ture while be­ing ap­plied which is an im­por­tant con­sid­er­a­tion when op­er­at­ing off­shore.

“Pure Polyurea is a ver­sa­tile and adapt­able ma­te­rial that is an ideal method of pro­tect­ing off­shore struc­tures,” Baker added. “To en­cour­age fur­ther up­take by the mar­itime mar­ket, RLA has a port­fo­lio of projects demon­strat­ing the ben­e­fits and cost ef­fec­tive­ness of Pure Polyurea.”

Where pipes and other equip­ment pen­e­trate the deck ar­eas of off­shore struc­tures, it is im­por­tant that liq­uids do not run down the pipes to the ocean be­low. Most off­shore rigs cover these pen­e­tra­tions with a butyl rub­ber ‘ boot’ that is taped to the pipe and the deck. How­ever, the rub­ber of the boot and the ad­he­sive can be de­graded by UV and salt ex­po­sure in a mat­ter of months.

To ex­tend the op­er­a­tional life of the deck pen­e­tra­tion boots, the butyl rub­ber and the ad­ja­cent steel sur­faces are usu­ally scuffed and cleaned prior to the ap­pro­pri­ate Rhino Lin­ings primer be­ing ap­plied. It is im­por­tant that all loose coat­ings, oils and dirt are thor­oughly re­moved be­fore ap­ply­ing the new flex­i­ble mem­brane. Sim­i­larly, the sur­round­ing equip­ment, pip­ing and deck sur­faces must be masked off to pro­tect against over spray.

One suit­able coat­ing ma­te­rial to use with the boots is Rhino Pure Polyurea (PP1195). Ac­cord­ing to Baker, when ap­plied at a thick­ness of 2000 mi­crons or greater, and ex­tend­ing 50 mm up the pipe and 100 mm onto the deck, cre­ates a liq­uid tight, weather re­sis­tant, flex­i­ble in­ter­face on all deck pen­e­tra­tions from 100 mm in di­am­e­ter with the long term dura­bil­ity de­manded by the marine in­dus­try.

RLA has been work­ing with spray-ap­plied polyurethane and Pure Polyurea since the mid-1990s and now man­u­fac­tures a range of con­sis­tent for­mu­la­tions in Aus­tralia which are suit­able for a di­verse range of ap­pli­ca­tions. “Pure Polyurea is a rel­a­tively mod­ern ma­te­rial that has been de­vel­op­ing rapidly dur­ing the past 15 years,” Baker said.

Pure Polyureas are formed when a liq­uid iso­cyanate is mixed un­der high pres­sure with an amine- driven resin so­lu­tion. Iso­cyanates are re­ac­tive be­cause the dou­ble co­va­lent bond at­tach­ing the car­bon atom to ni­tro­gen and oxy­gen atoms is eas­ily bro­ken to form sin­gle bonds in the more sta­ble tetra­he­dral con­fig­u­ra­tion around the car­bon atom.

The Rhino Pure Polyurea comes as a two- part so­lu­tion that is mixed un­der high tem­per­a­ture and pres­sure (3000 psi at 65ºC) in a spe­cially de­signed spray ap­pa­ra­tus. When ap­plied, the ex­cel­lent chem­i­cal cross link­ing pro­duces a dense but flex­i­ble sur­face. The high den­sity makes the coat­ing al­most im­per­vi­ous to abra­sion, wa­ter and chem­i­cals.

Pure Polyurea coat­ings ‘snap cure’ to form a solid sur­face in a few sec­onds and can be walked on with­out dam­age in less than a minute. An­other ad­van­tage is the abil­ity for it to be sprayed up to 6000 mi­crons thick (and greater) on a slop­ing or ver­ti­cal sur­face with­out sag­ging or run­ning. The sur­face of a RLA coat­ing is easy to main­tain, clean and re­coat if nec­es­sary.

Whereas epox­ies and paints form a solid, rigid shell, the flex­i­bil­ity of Pure Polyurea coat­ings al­lows them to move with the ex­pan­sion and con­trac­tion of the un­der­ly­ing struc­ture as tem­per­a­tures change.

Rhino Lin­ings Aus­trala­sia Pty Ltd (RLA) was formed in 2001 and es­tab­lished man­u­fac­tur­ing and distri­bu­tion ca­pa­bil­i­ties for the Aus­tralasian re­gion. RLA man­u­fac­tur­ers its spray ap­plied coat­ings at a fa­cil­ity on Aus­tralia’s Gold Coast and can draw on the more than 30 years’ ex­pe­ri­ence of its Amer­i­can par­ent. The com­pany sources all its ma­te­ri­als from lo­cal sup­pli­ers ex­cept for some very spe­cialised chem­i­cals which are im­ported from Amer­ica.

www.demm.co.nz/reader-en­quiry #160402


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