Materials Performance

AUG 2018

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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46 AUGUST 2018 W W W.MATERIALSPERFORMANCE.COM COATINGS & LININGS metal between the 8th tray and the chim- ney plate from the media. This was the only location in the absorber column where the presence of liquid water was expected . Water accumulation was unlikely at higher trays because of the dynamic environment in those areas. By applying this barrier, it was expected that the corrosion reaction that releases atomic hydrogen would not occur at this location. Thus, no free atomic hydrogen would be available to permeate the steel and increase the risk for cracking. The team decided to apply a coating system as the mitigation strategy rather than execute a major column repair that would potentially lead to the replacement of the entire vessel ring. The coating sys- tem consisted of a metal particulate-rein- forced polymer primer with a ceramic- filled epoxy topcoat. Surface preparation was done by grit blasting to a 3- to 4-mil ( 7 6 - t o 1 0 2 - µ m) p r of i l e , f o l l o w e d b y degreasing. The primer was applied using a plastic spatula applicator right after blast- ing to avoid oxidation of the metal. The curing time of the primer layer was 16 h at 78 °F (26 °C). Before the application of the second coat, the primer-coated surface was washed with a warm detergent solu- tion to remove any impurities, rinsed with clean water, and then allowed to dry. The topcoat was applied using the plastic spat- ula applicator to achieve a film thickness of 350 to 375 µm. It was allowed to cure for 72 h at 78 °F (26 °C). Figures 2 and 3 are photos of the coat- ing at the time of application, while Figures 4 and 5 are photos taken at the same loca- tion during the subsequent turnaround (four to five years later). Thorough visual inspection and hammer testing of the coat- ing system was done to detect possible bulging, deformation, softening, and pres- ence of voids. No visual changes were evi- dent since the coating application, and liq- uid accumulation was not observed at the barrier coating/metallic substrate inter- face. However, a disbondment test was not performed, keeping in mind that all pre- cautions for this coating application were strictly followed during its installation. The external surface of the column was exam- ined with U T phased array in the same location and using the same instrument set-up as when the defects were found. These results were cross referenced with the previous examination and no progres- sion of the flaw size was found. Hence, the unit was put back in service. Based on business development plans, the company constructed new GDUs that were designed with a SS cladding in this area to reduce the effects of corrosion and eliminate HIC susceptibility. These units have been functioning very well without cladding failure. Case History 2 Interviews and surveys were conducted with several other clients that run refiner- ies. Conversations with one refinery client are summarized below. Wet H 2 S damage is a repeat concern at refineries, specifically at weld seams. Base metals often blister, and blisters have been found when examining existing weld seams that were cut out. In the past, SS cladding would often be used to mitigate blistering on base metals. Many assets that benefit from coating application are in high-tem- perature process streams that facilitate permeation of hydrogen into the metal. Application of a coating system has been found to provide a mechanical barrier to the hydrogen generation reaction that occurs on the metal surface. This entailed assessing data on the H 2 S concentration of FIGURE 2 The photo shows the coating system applied to the chimney tray (looking above) when the flaws were discovered during the turnaround. FIGURE 3 Photo of the coating system applied to the chimney tray area up to the eighth tray.

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