CoatingsPro Magazine

MAY 2016

CoatingsPro offers an in-depth look at coatings based on case studies, successful business operation, new products, industry news, and the safe and profitable use of coatings and equipment.

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20 MAY 2016 COATINGSPROMAG.COM Notes From the Blog Editor's Note: Looking for " in the feld " information about the latest coating appli- cation techniques? We invite you to join the discussion. Te following are excerpts from the NACE Corrosion Network's (NCN) and NACE Coatings Network's email-based discussion groups for corrosion profession- als, with more than 1,000 participants. Te following excerpts have been selected for their potential interest to CoatingsPro readers. Tey have been edited for clarity and length. Authors are kept anonymous for publication. Please be advised that the items are not peer-reviewed, and opinions and sug ges- tions are entirely those of the inquirers and respondents. CoatingsPro and NACE do not guarantee the accuracy of the technical solutions discussed. You' ll enjoy a variety of opinions in this practical information exchange forum. For information on how to subscribe to these free list servers, click on the "Community" link on the NACE Website: www.nace.org. Application of Passive Fireproofing System Q: We are presently apply ing a passive fireproofing (PFP) system to an offshore structure but the curing is taking days vs. the seven hours specified in the coating manufacturer's data sheet. We also obser ved something like oil dripping out from each column. Please, what can we do? A: Verify it is being applied according to the specifcation and manufacturer's data sheet, then contact the manufacturer's techni- cal representative. A: W hat is the type of PFP you are using — intumescence epoxy, phenolic? Basically, PFP is an advanced coating used to resist fre (such as jet fre) within a specifed time. A: My experience is that the local PFP manufacturer tech support people might be reluctant to give a report that is critical of the applicator/ fabrication yard. I recommend you ask for a tech specialist from outside the region/country. PFP application, particularly intumescent material using heated plural-component spray equipment, presents so many opportunities for error. I don't know whose product you are using but the problems I have encountered are (1) product was not preheated prior to loading into the plural-component spray equipment, (2) Part A and B materials were not heated properly prior to pumping, (3) Part A and B material tempera- tures were not in the proper range at the mi xing manifold and gun due to inadequate heating of the hose bundle, (4) the manifold was not maintained, causing incorrect mi xing, (5) a worn mi xing screw did not allow complete mi xing, or (6) steel and ambient temperatures were below the manufac- turer's recommended minimum (a huge problem in w inter conditions). Role of Anions in Osmotic Blistering Q: Tere appears to be a focus on the role of anions in osmotic blistering, particularly chlorides, sulfates, and nitrates. However, my understanding is that osmosis has to do with water solubility and therefore the cations are as important as the anions. I am interested in your observations and experience. A: My understanding is that osmosis is the migration of a solvent through a semi-permeable membrane to establish the same ionic concentration on both sides of the membrane. Terefore, osmosis is a property of the solution and not what is dissolved in it. A: T he cations and anions are equa l ly impor tant because the cor rosion process depends on whether sa lts present have a cr itica l relative humid it y (CR H) enabling the absor p - tion of water to for m a cor rosion cel l. For ex ample, sod ium su lfate (Na 2 SO 4 ) is relatively noncor rosive because its CR H is above 90 percent, so a relative humid it y of less than 90 percent is insuf f icient to cause water absor ption by the sa lt. In cont ra st, c a lc iu m c h lor ide (C aC l 2 ) is h ig h ly cor rosive w it h a CR H of approx i m ately 30 percent, wh ic h mea ns a ny R H above t h at level lead s to for m at ion of a cor rosion cel l. T he w idespread u se of c a lc iu m c h lor ide i n A mer ic a for de -ic i ng road s produced severa l dec ades of "r u st buc kets," a lt houg h i mproved auto protec t ion s ystems h ave reduced t he problem. W hile it is true the osmotic process consists of establishing a solution equilibrium across a membrane, irrespective of salt compo- sition, this assumes the solution is constantly present, which is not neces- sarily true in the real world, except in an immersion environment. My ow n feeling is a combined mechanism of osmosis and CRH property would be a better explanation. A: As most of you will already know, osmosis is one of the colligative properties of solutions. It relates to the transpiration of a solvent across a semi-permeable membrane, in which PFP and FBE Coatings

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