Pro­tect your pipe­lines from cor­ro­sion

DEMM Engineering & Manufacturing - - MAINTENANCE MATTERS -

In the petro­chem­i­cal in­dus­try Cor­ro­sion Un­der In­su­la­tion (CUI) in pipe­line sys­tems con­sumes a sig­nif­i­cant per­cent­age of the main­te­nance budget.

A large por­tion of this money is spent on ex­pen­sive items such as ex­ter­nal pip­ing in­spec­tion, in­su­la­tion re­moval and re-in­stal­la­tion, paint­ing and pipe re­place­ments. CUI preven­tion strate­gies pro­vide long term and re­li­able preven­tion of CUI that move to­wards in­spec­tion-free and main­te­nance-free pip­ing sys­tems and sig­nif­i­cant main­te­nance cost re­duc­tions.

Coat­ing with TSA (ther­mal sprayed alu­minium), us­ing Met­alli­sa­tion flamespray equip­ment is one method that a num­ber of oper­a­tors within the petro­chem­i­cal in­dus­try have adopted. TSA is found to be a cost ef­fec­tive so­lu­tion com­pared to other sys­tems when re­viewed over the life­time of the fa­cil­ity.

One of Met­alli­sa­tion’s cus­tomers has an on­go­ing pro­gramme for ap­ply­ing TSA at a petro­chem­i­cal plant. One spe­cific project is a ma­rine jetty pipe­line that is used for the trans­porta­tion of lube oil and is ex­posed to the harsh ma­rine en­vi­ron­ment. Other projects on this site have in­cluded a full range of pipes and ves­sels, in­clud­ing work on live op­er­at­ing plant.

To en­sure the suc­cess of the ther­mal spray­ing process, the prepa­ra­tion of the pipe­line sur­faces is crit­i­cal. For this project the pipe­line sur­face was pre­pared by grit blast­ing with gar­net to give a sharp an­gu­lar pro­file for the TSA to bond to.

As part of the QA/QC process, the blast pro­file was reg­u­larly checked us­ing Tes­tex tape to en­sure it meets the re­quired 75-125 mi­cron spec­i­fi­ca­tion. The grit blasted sur­face was then given a vis­ual in­spec­tion, us­ing 10 x mag­ni­fi­ca­tion, to check the sur­face clean­li­ness and fin­ish.

The pipes are also given a ‘tape test’, which checks for dust con­tam­i­na­tion of the blasted sur­face. The tape sam­ple is vis­ually in­spected against white and black back­grounds for signs of dust par­ti­cles. The fi­nal qual­ity test is a salt con­tam­i­na­tion test. Once all of these tests have been passed the pipe­lines are ready to be ther­mal sprayed with alu­minium.

One ad­van­tage of the Met­alli­sa­tion equip­ment and process is the flex­i­bil­ity and long sup­plies, which pro­vide a safe work­ing en­vi­ron­ment and ease of use for the oper­a­tors. In this project, the gas bot­tles and com­pres­sor were sit­u­ated in a re­mote sup­ply area, which gave easy ac­cess to the gas cylin­ders and en­abled man­i­fold­ing for fewer cylin­der changes.

In el­e­vated ap­pli­ca­tions such as ves­sels and tow­ers, the cylin­ders can re­main on the floor while the spray sys­tem is el­e­vated tens of me­tres. This sit­u­a­tion there­fore re­quires less com­plex scaf­fold­ing as the heavy bot­tles are not scaf­fold mounted. The 30 me­tre sup­ply pack­age, con­sist­ing of gas, oxy­gen and air, was fed from the over­head sup­ply area down to the con­trol panel.

The pis­tol is then a fur­ther 10m away from the con­trol panel. This setup al­lows around a 60m length of pip­ing to be sprayed with­out hav­ing to move the cylin­ders and air com­pres­sor, giv­ing sig­nif­i­cant pro­duc­tiv­ity ben­e­fits in a dif­fi­cult en­vi­ron­ment.

The con­trac­tor on this spe­cific job­site is us­ing two Met­alli­sa­tion MK73 flamespray sys­tems in dif­fer­ent spray lo­ca­tions. Once the blast­ing and in­spec­tion is com­pleted, the TSA ap­pli­ca­tion starts. Typ­i­cally, blast­ing and in­spec­tion is com­pleted in the morn­ing tak­ing ap­prox­i­mately four hours.

The TSA is ap­plied in the early af­ter­noon for around three hours and the fi­nal sealant ap­pli­ca­tion at the end of the day.

The MK73 de­flected ex­ten­sion is per­fect for those dif­fi­cult to ac­cess ar­eas com­monly found at petro­chem­i­cal sites, and has been de­signed specif­i­cally for this ap­pli­ca­tion area. It comes in three lengths, 150mm, 300mm and 450mm. The ex­ten­sion unit can spray di­rectly for­ward or at a de­flected an­gle up to 90º by vary­ing the de­flec­tor air pres­sure.

The de­flec­tion noz­zle can also be ro­tated through 180º to al­low spray­ing in a 360º arc around the pis­tol.

Fol­low­ing the ap­pli­ca­tion of the TSA, the pipe­lines in this spe­cific ap­pli­ca­tion were sealed with In­tertherm 50 sealer, which was ap­plied un­til full pen­e­tra­tion was achieved. In some CUI re­lated en­vi­ron­ments, no sealer is ap­plied, es­pe­cially where the spray area is op­er­a­tional and hot.

To sup­port the QA/QC process the spray oper­a­tors pro­duced wit­ness plates on a daily ba­sis, which were then tested for ad­he­sion to en­sure it met the min­i­mum 1000 psi – 6.9PMa coat­ing thick­ness.

For more in­for­ma­tion on the CUI or ther­mal spray equip­ment see www.met­alli­sa­

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