Valve Durability
Figure 5 : SEM images and EDS analysis of cross-sections of Co-based coatings after fouling at 450 ° C for 2 hours : samples Co-1HT and Co-3HT .
microstructure , and surface energy significantly influences fouling mechanisms . Finding alloy substrates that are completely immune to fouling in refining and petrochemical applications remains a challenge .
Role of coatings in fouling mitigation
The solution to fouling and sulphidation corrosion in hydrocracking processes appears to be coatings . Desired coating properties include engineered microstructures that maintain wear and corrosion resistance in these aggressive environments . The coated substrates under simulated resid upgrading conditions exhibited significantly improved resistance to fouling and sulphidation corrosion compared to uncoated materials . However , standard thermally sprayed and fused cobalt-based coating ( Co-1 ) did not prevent sulphidation and coke buildup , indicating the need for further optimisation . A comparative study of standard ( Co-1 ) and optimised ( Co-3 ) cobalt-based coatings using optical imaging processing method demonstrated a significant reduction in fouling intensity , from 96 % to just 3 % with the optimised coating ( see Figure 4 ). Further destructive testing confirmed that sulphur and coke buildup were significantly higher in Co-1 coating , highlighting the critical interplay between sulphidation and fouling mechanisms ( see Figure 5 ). This synergy accelerates material degradation but also reinforces the superior performance of Co-3 coating in resid upgrading environments .
Predicting fouling and corrosion in resid upgrading processes
Based on our experimental testing data , a phenomenological model was developed to describe different fouling modes in three distinct scenarios ( see Figure 6 ): 1 . Fouling with temperature , catalyst , and hydrogen : similar to a slurry cracker , where the catalyst is present in the line .
2 . Fouling with temperature and hydrogen only : similar to an ebullated bed , where most of the catalyst remains inside the reactors .
3 . Fouling with temperature only : similar to a coker , where neither hydrogen nor catalyst is present .
Our findings suggest that fouling mechanisms are influenced by the interaction of temperature , catalyst and hydrogen . In the first scenario , sulphidation attacks grain boundaries , leaching alloying elements such as iron , nickel , titanium and aluminium . The corrosion products act also as catalysts , increasing the decomposition rate if hydrocarbons locally which increase the sulphur and sulphidation rate . This intergranular corrosion roughens the surface , making it more prone to coke adhesion . However , due to higher conversion rate , the amount of adherent coke is less than in the second and third scenarios . In the second scenario the sulphidation is more uniform . Although there is slight tendency toward the grain boundaries , leaching of alloying elements is less pronounced . While the amount of coke buildup is greater than in first scenario , coke adhesion on the sulphide layer is less . The sulphide-rich scale is thicker than in first scenario and tends to delaminate . The third scenario sees the highest coke buildup due to the lowest conversion rate , but with a more stable oxide layer providing some protection . The model confirms that while hydrogen and catalyst increase conversion rates , they also accelerate corrosion , necessitating advanced coatings for valve protection in high-conversion processes .
Acknowledgments
We would like to thank the team of researchers from the University of Montreal for their dedication to this project , particularly Dr . Fellipy Rocha , who transitioned from student to PhD graduate during this research . We also acknowledge the Multisectorial Industrial Research Chair in Coatings and Surface Engineering ( MIC-CSE ), which Velan has funded since 2012 alongside other industrial partners . Based at Polytechnique Montreal on the University of Montreal campus , MIC-CSE stands as the second-largest industrial research chair in Canada . Our thanks go to all contributors for their teamwork and invaluable efforts in advancing our understanding of the fundamental mechanisms governing our products , ultimately enhancing their reliability and performance . Lastly , we appreciate the financial support from the Canadian and Quebec governments , which has been instrumental in making this research possible .
40 Valve World March 2025 www . valve-world . net