Cor­ro­sion: fo­cus on en­vi­ron­men­tally friendly solutions

DEMM Engineering & Manufacturing - - FRONT PAGE -

The eco­nomic im­pact of cor­ro­sion rep­re­sents a cost of bil­lions of dol­lars to the econ­omy ev­ery year. Plan­ning for cor­ro­sion con­trol and mit­i­ga­tion helps to min­imise the cost im­pli­ca­tions of ig­nor­ing the ef­fects by re­duc­ing the main­te­nance time and in­creas­ing an as­set’s util­i­sa­tion.

One way to pro­tect an as­set from cor­ro­sion is to phys­i­cally iso­late a struc­ture from the en­vi­ron­ment by ap­ply­ing a sur­face coat­ing. How­ever, it is not only the out­side that needs pro­tec­tion. The walls and floors of hospi­tals, in­dus­trial fa­cil­i­ties, com­mer­cial of­fices and other built struc­tures re­quire pro­tec­tion. Ad­di­tion­ally, in­ter­nal ser­vices ( pipes, equip­ment, mo­tors, boil­ers, etc.) need to be pro­tected.

Pro­tec­tive coat­ings are not just paints. They are engi­neered prod­ucts that un­dergo rig­or­ous prod­uct de­vel­op­ment and test­ing to pro­vide spe­cific prop­er­ties that will pro­tect a struc­ture from its service en­vi­ron­ment or pos­sess par­tic­u­lar char­ac­ter­is­tics static dis­si­pat­ing, abra­sion re­sis­tance, ther­mally in­su­lat­ing etc. that make it a func­tional coat­ing.

Dur­ing the past 20 years, Gra­ham Carlisle, Prin­ci­pal Cor­ro­sion and Coat­ing En­gi­neer at IAS Group in Western Aus­tralia, has worked with many con­trac­tors and sup­pli­ers on projects work­ing to pre­vent or re­me­di­ate cor­ro­sion. “When work­ing with ex­ist­ing fa­cil­i­ties such as a ho­tel or hos­pi­tal, a ma­jor con­straint is get­ting ac­cess,” he said. “It is very dif­fi­cult to shut down a busy 24 hour a day pub­lic health fa­cil­ity, so we have to care­fully plan how and when works are car­ried out.”

The rapid cure times of mod­ern spray-ap­plied polyurea, methyl methacry­late, epoxy and polyurethane coat­ings make them ideal for use in fa­cil­i­ties that can­not eas­ily be shut down. Min­imis­ing dis­rup­tion to the oper­a­tion of hospi­tals, ho­tels and pro­duc­tion plants is a key con­sid­er­a­tion.

Be­fore a coat­ings pro­ject is un­der­way, there are sev­eral as­pects that need to be care­fully man­aged. “It is im­por­tant to un­der­stand the com­pe­tence of the ap­pli­ca­tor and en­sure that the main con­trac­tor un­der­stands all the steps needed to un­der­take the coat­ing process, the suc­cess re­quire­ments and does not ac­cept lower qual­ity ma­te­ri­als that do not meet spec­i­fi­ca­tions,” said Peter Dove, Prin­ci­pal Ma­te­ri­als Con­sul­tant at GHD one of the largest con­sul­tancy en­gi­neer­ing groups in Aus­tralia. GHD has a Ma­te­ri­als Tech­nol­ogy Group in­volved in solv­ing a range of dura­bil­ity and cor­ro­sion is­sues and projects.

The Aus­tralasian Cor­ro­sion As­so­ci­a­tion ( ACA) works with com­pa­nies such as IAS Group and GHD as well as aca­demic in­sti­tu­tions to re­search all as­pects of cor­ro­sion in or­der to pro­vide an ex­ten­sive knowl­edge base that sup­ports best prac­tice in cor­ro­sion man­age­ment, en­sur­ing the en­vi­ron­ment is pro­tected, pub­lic safety en­hanced and economies im­proved.

In ad­di­tion to pro­vid­ing a phys­i­cal bar­rier, sur­face coat­ings can also be used as ther­mal in­su­la­tion de­pend­ing on their com­po­si­tion. Coat­ings are avail­able that have high ti­ta­nium diox­ide con­tent which re­flects heat when used on the ex­ter­nal walls of build­ings.

One emerg­ing mar­ket for coat­ings tech­nol­ogy is in pro­tect­ing HVAC duct­work in­side build­ings and com­mer­cial fa­cil­i­ties. “By us­ing coat­ings with the ap­pro­pri­ate ther­mal char­ac­ter­is­tics as­set own­ers can achieve per­for­mance gains with less ex­pense,” said Carlisle. “There is no need for old style fi­brous lag­ging that de­grades over time, col­lects dust and has to be re­placed pe­ri­od­i­cally and can lead to hid­den cor­ro­sion is­sues un­der the in­su­la­tion.”

Spray- ap­plied ther­mally in­su­lat­ing coat­ings ( TIC) can be used when in­su­lat­ing a build­ing’s duct­work, pipes and machin­ery often in­volv­ing com­plex

ge­ome­tries around valves and levers. Ap­ply­ing such coat­ings is much eas­ier and can achieve the same per­for­mance re­sults of tra­di­tional lag­ging more quickly and with less la­bor. TICs di­rectly ad­here to the sub­strate, thus min­imis­ing or elim­i­nat­ing the space be­tween the sub­strate and con­ven­tional in­su­la­tion that can hold mois­ture. Re­plac­ing tra­di­tional fi­brous in­su­la­tion with an in­su­lat­ing coat­ing re­duces en­ergy us­age and pro­tects the sys­tem from the prob­lem of cor­ro­sion un­der in­su­la­tion (CUI). It also has the ad­di­tional ben­e­fit of mould and mois­ture re­sis­tance, which in turn im­proves over­all air qual­ity in­side build­ings.

TICs can also be used on the roof and walls of a build­ing. When prop­erly in­stalled and main­tained, a coat­ing can help an as­set owner achieve en­ergy sav­ings as well as ex­tend the service life of a build­ing. The lat­est coat­ings can with­stand ex­tended ex­po­sure to wa­ter, hu­mid­ity, tem­per­a­ture ex­tremes, ul­tra­vi­o­let rays, oxy­gen, and at­mo­spheric pol­lu­tants.

Coat­ings used in the hos­pi­tal and ho­tel sec­tor are mostly epoxy- based sys­tems. “The choice as to what coat­ing is used must be based on an as­sess­ment of the en­vi­ron­ment where it is used and what it will be ex­posed to,” Dove said.

The per­for­mance char­ac­ter­is­tics are de­ter­mined by the dif­fer­ent chem­istry of the var­i­ous coat­ings. “The cur­ing tem­per­a­ture of a coat­ing im­pacts the choice of ma­te­rial,” Dove said. “At any­thing less than 10 ºC, it is un­likely that epox­ies would be used.” Al­ter­na­tive coat­ings are re­quired for use in sit­u­a­tions such as com­mer­cial freez­ers. Slight changes in a coat­ing’s for­mu­la­tion changes its bal­ance of prop­er­ties and thus the way it per­forms un­der dif­fer­ent en­vi­ron­men­tal con­di­tions.

If a coat­ing is to be ex­posed to dif­fer­ent chem­i­cals, the ma­te­rial used must be of the ap­pro­pri­ate type. Carlisle said that caus­tic sub­stances re­quire a dif­fer­ent ma­te­rial from those used for acids. “In a brew­ery, the in­ter­nal coat­ings of floors and walls are mostly ex­posed to the caus­tic wash used to clean the tanks and pipework. In a hos­pi­tal or re­search lab­o­ra­tory, there may also be many acidic sub­stances used.”

Sim­i­larly, dif­fer­ent op­er­at­ing pro­cesses re­quire al­ter­na­tive coat­ings; if there is an ex­trac­tion flue as­so­ci­ated with a process, the in­ter­nal coat­ing must be able to tol­er­ate both the tem­per­a­ture of the hot gasses pass­ing over it as well as the cor­ro­siv­ity of them. Ac­cord­ing to Gra­ham Carlisle ev­ery in­crease of 10 ºC may ap­prox­i­mately dou­ble the cor­ro­siv­ity of a gas or liq­uid.

Ac­cord­ing to Dove, there are a range of fac­tors that need to be con­sid­ered. “While coat­ings are an ef­fec­tive treat­ment, some­times it might be more ef­fec­tive to change the ma­te­rial for ex­am­ple, stain­less steel used to make the un­der­ly­ing struc­ture. The risks as­so­ci­ated with a sur­face must also be as­sessed, es­pe­cially if liq­uids are be­ing han­dled. A tiled sur­face or plas­tic mem­branes may be the most ap­pro­pri­ate in cer­tain sit­u­a­tions in a ho­tel or hos­pi­tal.”

The safest way to en­sure a pos­i­tive coat­ing out­come is to se­lect a coat­ing from a rep­utable coat­ing man­u­fac­turer with proven case his­to­ries that can be ver­i­fied, and en­gage an ap­pli­ca­tor trained and en­dorsed by the man­u­fac­turer.

For re­me­di­a­tion work, while spray-ap­ply­ing is usu­ally the most ef­fec­tive ap­pli­ca­tion method, on in­side sur­faces, brush, roller or trowel ap­pli­ca­tion is often used. To re­me­di­ate con­crete struc­tures, it is im­por­tant to use a ma­te­rial that tol­er­ates al­kali. If there is a high mois­ture level in the con­crete mix, an al­ter­na­tive coat­ing ma­te­rial may be re­quired. A pro­ject came to Dove from a casino in the Mid­dle East where the high resid­ual mois­ture con­tent of the con­crete used had caused the floors in some ar­eas of the build­ing to com­pletely de­lam­i­nate.

It is im­por­tant that a pro­tec­tive coat­ing pro­ject is care­fully planned. One thing to avoid is un­der­es­ti­mat­ing the tech­ni­cal com­plex­ity of a pro­ject, es­pe­cially if the coat­ing is to be ap­plied to an ex­ist­ing struc­ture.

Pro­tec­tive coat­ings projects are usu­ally un­suc­cess­ful for rel­a­tively few rea­sons. Plan­ners often do not fully com­pre­hend the com­plex­ity of many coat­ings projects and, as a con­se­quence, fail to in­vest the time and re­sources to man­age it ef­fec­tively which re­sults in sub­stan­tial cost im­pli­ca­tions when things go wrong. It is im­por­tant to have the knowl­edge to ask the ap­pro­pri­ate ques­tions and un­der­stand what the lim­its are when faced with the many op­tions avail­able.

The lack of de­tailed de­sign in­for­ma­tion for a struc­ture some­times means that there can be poor se­lec­tion of struc­tural ma­te­ri­als. For ex­am­ple, if dis­sim­i­lar met­als are used, this re­sults in re­strict­ing the coat­ing op­tions avail­able a coat­ing for one metal is often in­ap­pro­pri­ate for another.

The cost of ap­ply­ing a sur­face coat­ing varies de­pend­ing on whether it is ap­plied in a work­shop or on- site. Ap­ply­ing a coat­ing can vary be­tween $ 80 per square me­tre in a work­shop to $300 per square me­tre or higher on- site. Carlisle and Dove ad­vo­cate not scrimp­ing on a coat­ings spec­i­fi­ca­tion, or the qual­ity ver­i­fi­ca­tion, as th­ese could be some of the best dol­lars spent on a pro­ject.

There are also many stan­dards re­lat­ing to the ap­pli­ca­tion of pro­tec­tive sur­face coat­ings but some­times com­pro­mises may need to be made. When plan­ning pro­tec­tive coat­ings it is im­por­tant to take into ac­count a num­ber of fac­tors, in­clud­ing the op­er­at­ing en­vi­ron­ment, ac­cess to the struc­ture and cli­mate all of which im­pact the cost of the pro­ject. A good coat­ings spec­i­fi­ca­tion will ref­er­ence rel­e­vant Aus­tralian and in­ter­na­tional stan­dards, such as AS/NZ 2312 and cat­e­gorise the service en­vi­ron­ment ac­cord­ing to its cor­ro­siv­ity and then nom­i­nate an ap­pro­pri­ate sys­tem based on the de­sired de­sign life of the coat­ing.

The health and safety anal­y­sis of a pro­ject must look at how to ef­fec­tively pro­tect a struc­ture and ad­dress any en­vi­ron­men­tal con­sid­er­a­tions. It must also con­sider how to prop­erly ap­ply the coat­ing to min­imise its ef­fects on the sur­round­ing ar­eas as well as pro­tect the tech­ni­cian who might be work­ing in a har­ness, teth­ered me­tres above the ground.

Many old style coat­ings were ef­fec­tive but not very safe ac­cord­ing to to­day’s un­der­stand­ing of the health ef­fects of ‘pro­tec­tive’ sub­stances such as red lead and as­bestos. A re­cent pro­ject of Dove’s in­volved the restora­tion of one of the his­toric build­ings used by a ma­jor ed­u­ca­tional in­sti­tu­tion in Mel­bourne. “It was a rare sit­u­a­tion where we were able to see the works be­ing done from start to fin­ish,” Dove added. “Con­structed in the 1870s, there were many lay­ers of dif­fer­ent paints and other coat­ings used over the years.” Spe­cial paint strip­pers were re­quired to re­move sev­eral dif­fer­ent coloured coat­ing lay­ers from the build­ing be­cause anal­y­sis in­di­cated some had up to 30 per­cent lead in them and the un­der­ly­ing ren­der could not be dam­aged by more ag­gres­sive forms of coat­ing re­moval. Be­fore the ap­pli­ca­tion of a breath­able min­eral sil­i­cate coat­ing, the ren­der needed ex­ten­sive re­pairs by her­itage stone ma­sons to re­store the dura­bil­ity of the façade. Another vi­tal as­pect of coat­ings projects is to have cer­ti­fi­ca­tion that the job com­plies with all the ap­pro­pri­ate leg­is­la­tion, reg­u­la­tions stan­dards and pro­ject spec­i­fi­ca­tions through en­gag­ing NACE or ACA qual­i­fied coat­ings in­spec­tors for steel or con­crete coat­ing ap­pli­ca­tions.

The Aus­tralasian Cor­ro­sion As­so­ci­a­tion ( ACA) works with com­pa­nies such as IAS Group and GHD as well as aca­demic in­sti­tu­tions to re­search all as­pects of cor­ro­sion in or­der to pro­vide an ex­ten­sive knowl­edge base that sup­ports best prac­tice in cor­ro­sion man­age­ment, en­sur­ing the en­vi­ron­ment is pro­tected, pub­lic safety en­hanced and economies im­proved.


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