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 73 of 92

COATINGSPRO MAY 2018 73 low vapor pressure, it is, on occasion, included in the percent solids calcu- lation to make the coating appear to produce a higher DFT. It is not reacted into the coating matrix. As such, when the coating is heated, the " benzene methanol " is lost via molecular migra- tion out of the coating. One sees from the GC/MS data of the failed coating that there was no benzyl alcohol remaining in the delaminated coating. e freshly applied and cured coating contains a large amount of the diluent. Conclusions e root cause of the lining failure in the separator was due to the fact the coating was applied to an improperly cleaned surface at dry film thicknesses way in excess of what was specified. e product data sheet specifies a dry film thickness of between 650 µm and 1,000 µm (25.6 and 39.4 mils). Both field and laboratory measure- ments showed dry film thicknesses ranging from 2250 µm to 3110 µm (88.6 to 122.4 mils). e product data sheet recommends that a plural component spray machine be used in its application. It also recommends that the product be preheated prior to appli- cation and that solvents not be used. e reason for this is that the product has a short pot life and will start cross linking as soon as it's mixed, increasing its viscosity and making it more diffi- cult to spray to the specified thickness. None of these recommendations were followed. Instead, per the product application report, a regular airless pump was used, thinner (xylene) was added, and the product was not preheated. ese events greatly contributed to the excessive film thick- nesses observed. Additionally, the photos from inside the vessel clearly depict a coating suffering from severe shrinkage stress and subsequent cracking and delamina- tion. e presence of half-moon-shaped cracks is an indication of this failure mode. e size of the half-moon cracks is seen as an indication of the degree of adhesion of the coating at the location of the cracks. e larger cracked pieces have low, compromised adhesion, and the smaller half-moon cracks occur at locations of better adhesion. e shrinkage stress results The lining failure was determined to be due to improper surface prep and excessive dry film thickness. Failure on FPSO Vessel 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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