CoatingsPro Magazine

MAY 2017

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 67 of 84

COATINGSPRO MAY 2017 67 ranged from 95‒110 °F (35.0‒43.3 °C), making it difficult to work outside. Part of the team started visual inspections to look for signs of failures and substandard work. After a week of looking through the specifications and establishing an Inspection Testing Plan, field visual inspections and testing of the protective coatings and lining systems commenced. Noticeable defects were immediately apparent, includ- ing pinholes, installation mechanical damage, holidays, and delamination, among other prevalent defects. Part of the team's scope was to assess the quality of piping, which arrived at an offsite port. e inspec- tions included approximately ~29,500 feet (9 km) of large bore 8" (20.3 cm) diameter pipe, which had been fabri- cated and shop-coated in 60-foot (18.3 m) sections. e coating system included an inorganic zinc silicate, an organic convertible two-part epoxy, and a polyurethane coating. Upon initial evaluation of the pipe, it was noted that the surface was wet. We wiped it to look for defects, such as pinholes. Surprisingly, the entire convertible polyurethane protective coating topcoat rubbed off on the rag with the use of a simple water-borne solvent. is wipe testing exposed the underlying epoxy coating, which is also a convertible coating. Convertible coatings cure by polymerization, in other terms by cross linking. is pipe had been coated more than three weeks prior to being delivered, indicating that there was a sufficient amount of time for the coating to dry. W hen performing a rub test on the intermediate epoxy coatings, it also exhibited significant lifting on the rag. Overall, the entire lot of piping (~29,500 feet, 9 km) had to be rejected due to the incorrect curing of the polyurethane and epoxy coatings. Eventually, the balance of the lot (193,570 feet, 59 km) was inspected at a later date and also rejected due to similar defects. In addition to the uncured coating in the top two layers rubbing off, pinholes were evident across nearly the entire lot of pipe. is could be attributed to over-coating before the underlying epoxy reached its recoat time and cure, causing solvents to escape though the epoxy and then through the polyurethane. e coating was dry to the touch, and it did not feel tacky. is raised concerns because not only was the pipe fabricated from this particular shop, but the structural steel at the plant was also fabricated at this shop as well. is resulted in the client's approval to perform destructive testing of the structural steel. When pipe surfaces were wiped, the entire convertible polyurethane topcoat rubbed off with a rag and water-borne solvent. In addition to the uncured coating in the top two layers rubbing off, pinholes were evident across nearly the entire lot of pipe. Despite three weeks between delivery a n d t e s t i n g , w i p i n g e x p o s e d t h e underlying epoxy coating. Power Plant Coatings

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