CoatingsPro Magazine

MAY 2018

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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Page 74 of 92

74 MAY 2018 COATINGSPROMAG.COM after the coating is "set" and unbound moieties, or the individual chemicals, in the coating migrate to the surface and escape from the coating matrix. is constitutes a loss of volume of the coating material, and this loss of coating volume within the coating matrix produces the shrinkage stress. e actual degree of stress that develops and its propensity for damage is dependent on some basic variables. e coating's ability to tolerate the shrinkage stress in each location is dependent on the degree (aka quality) of adhesion and the depth of the anchor profile. e substrate anchor profile is extremely important in assisting in lateral support (parallel to the substrate) in the face of the severe stress produced by the loss of coating volume. Final overall film thickness is a major variable since the degree of shrinkage stress that develops at a location depends on the percentage of coating volume that has been lost. Other variables include the number and thickness of coats as well as cure time between coats. is shrinkage stress applies a severe pulling force against the coating parallel to the substrate surface. With any compro- mise in adhesion, the coating will crack (usually in half moons) to relieve the tension as it develops parallel to the substrate surface. From the GC/MS data, the shrink- age stress was generated by the volume loss of the benzyl alcohol after the coating had set. To a minor degree, other solvents added to assist the spray application were also lost causing additional shrinkage stress. In reality, the cured coating is not 98 percent solids as advertised. Because the coating was subjected to heating cycles, the volume of the benzyl alcohol lost produced shrinkage stresses greater than the coating could tolerate with the Sa 2.5 blast job and low profile. e substrate surface prep was not properly completed prior to coating application. e lining failures on this FPSO are proof that contractors need to follow the manufacturer's product data sheets for all aspects of the application. And even then, things can still go wrong. CP John Petersen, ow ner of Petersen Consu lt ing , is a NACE Cer t if ied Coat ing Inspector – Level 3 and completed his Of fshore Cor rosion A ssessment Tra ining (O-C AT). For more infor mat ion, contact: Petersen Consu lt ing , w w w.petersencoat ingconsu lt Failure on FPSO Vessel R E G I S T E R T O DAY F O R T H E W O R L D'S P R E M I E R WAT E R C O N F E R E N C E JUNE 11–14 LAS VEGAS, NEVADA AWWA.ORG/ACE18 Re ad e r In qui r y at co ati n g sp ro m a m /i n q0518

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