Materials Performance

NOV 2014

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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Page 46 of 92

44 NOVEMBER 2014 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 53, NO. 11 Continued f rom page 43 BLOG A: I recommend obtaining a copy of the EPRI Report, "Linings at Power Plants." In all power plant applica- tions where high temperature was an issue, polysiloxane applications received the lowest failure ratings according to this report. Use of epoxy accelerators Q: Does anyone have f ield experi- ence with epoxy accelerators? I would appreciate your opinions on the use and possible limitations of these systems. A: Assuming that you are talking about two-component epoxy coatings, the speed of cure can be adjusted depending on the application temperatures (ambient and surface). You should speak with the manufac- turer and supplier of the epoxy since they are in the best position to provide the ty pes of cure you require. In any case, cure accelerators (or retarders) provided by anyone other than the original formu- lator should not be used as they may alter the chemistry and performance of the epoxy. A: I agree that you should only use the accelerator recommended by the manufacturer of the coating you are using. Read and follow the specifed appli- cation procedures for that particular product. Do not use an epoxy accelerator in urethane, nor use a urethane accelera- tor in epoxy. A: Be aware that the use of accelera- tor additives in epoxy chemistry alters the physical properties from the original product. Outward indicators for change can be increased fexibility, increased brittleness, and yellowing tendencies. Check with your epoxy manufacturer about adding accelerator to the base/catalyst mixture, or replacing a portion of the catalyst with the acceler- ator. If you just add accelerator without reducing the catalyst amount, the mix ratio is changed. A: Do not forget that the result of obtaining a faster cure is also at the expense of a shorter pot life and reduced recoat window. Removal of vinyl ester glass flake epoxy Q: We have a vessel that is coated with vinyl ester glass f lake epoxy. The average thickness is ~1,750 ┬Ám dry f ilm thickness. Our job is to remove this coating and recoat with a 100% solvent-free epoxy. The coating is in quite good condition. Can anyone advise how best to remove this coating? A: In projects I have been involved in where the exact same product had to be removed, all existing coatings were removed with ultrahigh-pressure water jetting (UHPW J) before any

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