CoatingsPro Magazine

SEP 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 68 of 83

COATINGSPRO SEPTEMBER 2018 69 coat any number of hopper car config- urations. e area surrounding the coating line was immaculately clean and was subject to frequent and rigor- ous housekeeping measures. e hopper cars in question were prepared and coated in the follow- ing steps: 1. Surface preparation consisted of steel shot/grit blasting using automated blast nozzles controlled by computer. 2. The hopper car interiors were inspected by NACE-certified inspec- tors, and manual spot blasting was performed as indicated by the inspection results. 3. The car was moved to the first of two coating application booths. In the first coating application booth, the hopper car interior would be computer-controlled coated with the first of two identical coats. The two coats were color contrasted, and the first applied coat was then inspected. 4. The car moved to a forced-curing oven where it cured by heating the car substrate to 130 °F (54 °C) in a computer-controlled curing oven. The accelerated curing substrate temperature and time was as speci- fied by the coating manufacturer. 5. The second coat was then applied in a second computer-controlled spray booth. The second coat was then inspected. 6. The car moved into a second computer-controlled curing oven; the second coat was then force cured, again by heating the car substrate to 130 °F (54 °C). The accelerated curing substrate temperature and time was as specified by the coating manufacturer. 7. After completion of heat curing, the finished hopper car lining was inspected, and the car was readied for delivery to the customer. W hen the hopper cars were delivered to the customer, no visual precursors of the impending lining system failure were apparent. e customer loaded the cars with high-purity plastic pellets to be deliv- ered to a recipient that manufactured high-end products, such as artificial heart valves. Upon delivery of the plastic pellets, the recipient noticed coating chips mixed in. W hen the client emptied some of the affected cars, it was apparent that the coating chips were coming from a failure/disbond- ment of the coating applied to the sloped bottom plates of the hoppers. e recipient subsequently rejected the shipments of plastic pellets, and the cars were returned to the owner. The Lining Failure Analysis e owner of the hopper cars made the decision to have all of the cars relined, and a failure analysis was performed to identify the problem(s) that had caused the lining failure. e cars were subsequently sent to many shops to be relined due to the sheer number of cars involved. is is when I was called in as part of a team to identify the cause(s) of the lining failures. Following my failure analysis protocol outlined earlier, I conducted the following investigations: Step 1: Define the failure I determined that essentially all of the lining failures were occurring in the sloped panels at the bottom of each hopper, and the failure consisted of spotty delamination of the second coat from the first coat. Step 2: Complete interviews and examine records I examined the computerized records and NACE-inspector inspection reports for the lot of cars and found nothing out of spec. We interviewed the inspectors. Step 3: Review the specification I reviewed the project lining specifi- cation and found nothing that would explain the failures. Step 4: Make field observations As I mentioned before, the lining facility was very clean, the equip- ment was well-maintained, and the operations personnel were knowledgeable. e hopper car facility management team members were very cooperative and eager to identify the lining applica- tion problem. Step 5: Conduct laboratory examinations Samples of the failed lining as well as wet samples of the lining materi- als were sent to a qualified coatings laboratory. Detailed analyses were performed, but no anomalies were found. No foreign materials, amine blush, etc., were found on the back side of any of the delaminated top coat samples from the failed lining, and the wet coatings were found to be chemically sound. The hopper cars held plastic pellets, and the delamination problem was observed when the pellets were delivered to the recipient; coating chips were mixed in. Railcar Lining Delamination

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