Figure 4 : Fouling intensity comparison of Co-1HT and Co-3HT after fouling test : optical image and postimage treatment . π www . valve-world . net Valve World March 2025 39
Valve Durability
Figure 3 : Cross-section SEM images and EDS maps of IN718 post-fouling test .
Persistent challenges : fouling and coke deposition
As residue upgrading technologies continue to evolve , one persistent challenge across all processes is fouling and coke deposition in stagnant areas ( see Figure 1 ). This buildup can damage sealing surfaces , increase torque requirements , and reduce operational efficiency . One common mitigation strategy is purging valves with clean fluid , but this approach comes with its own complexities , including additional maintenance and unexpected outages . The tendency of materials to accumulate coke varies , making material selection a critical factor in enhancing long-term performance . Through ongoing discussions with industry experts and close collaboration with endusers , Velan is involved in the development of advanced surface treatments designed to minimise fouling , ensuring more reliable and efficient operation across various residue upgrading processes .
component location , with different alloys exhibiting similar degradation patterns . These findings , coupled with discussions with end-users , catalysed R & D efforts to replicate the hydrocracking environment in a laboratory setting . While smallscale reactors cannot fully mimic refinery environments , they provide critical insights into corrosion and fouling mechanisms in a controlled setting . Custom experimental reactors were developed to operate at refinery temperatures and pressures . Samples were exposed to bitumen sourced from both a licensor and an Alberta refinery at 450 ° C ( 842 ° F ) and 114 bar ( 1650 psi ); in addition , testing was performed with hydrogen and catalyst and without catalyst . Nickel-based alloys , commonly used in these harsh environments , offer excellent high-temperature strength and corrosion resistance . However , detailed post-exposure analysis revealed distinct three-layer degradation : an oxygen-rich layer adjacent to the substrate , a sulphur-rich layer above the oxide , and a carbon-dominant outermost layer ( see Figure 3 ). These layers closely mirrored those observed in field samples , validating the failure mechanisms encountered in service . A fundamental understanding emerged : the interplay between alloy composition ,
Understanding the challenges : from field insights to innovation
The mechanisms behind fouling and coke buildup remain poorly understood . To gain deeper insights , field visits to resid upgraders were conducted to gather firsthand information on recurring valve performance issues and acquire failed components for metallurgical analysis . Microstructural evaluations of these components revealed scale buildup , characterised by distinct sulphidation and oxidation patterns , accompanied by preferential depletion of alloying elements ( see Figure 2 ). The thickness of this buildup varied based on service duration and
Figure 4 : Fouling intensity comparison of Co-1HT and Co-3HT after fouling test : optical image and postimage treatment . π www . valve-world . net Valve World March 2025 39