A major problem in hydrocarbon processing systems is the buildup of carbon on the surface of steel or stainless
steel components—coking. Coking often is initiated by catalytic action of nickel or carbon impurities or additives
in the steel used to construct the processing system components.
Restek chemists are working in conjunction with the Fuel Science Program at the Pennsylvania State University to
quantify the effects of Siltek® and Silcosteel® treatments on the formation of coke.(1) A
Silcosteel®-treated system exhibits a 4-fold reduction in coke formation, compared to untreated stainless
steel, but a modified Silcosteel® treatment, Silcosteel®-AC, can provide an 8-fold reduction. The
Silcosteel®-AC or Silcosteel® layer forms a barrier between the hot hydrocarbon stream and the
coking-susceptible steel substrate, and eliminates catalytic breakdown in the hydrocarbon stream. With the
elimination of surface catalytic activity, carbon will not chemically adhere to the surface.
Current work indicates that the only mechanism of carbon formation in a Restek-treated system is the result of
coking within the fluid phase. This material settles on the surface without adhering, and is easily removed by
agitating the surface. Now, instead of “burning” out coke with oxygen at high temperatures, deposited carbon can
simply be rinsed away.
Applications for Silcosteel®-AC coking control treatment include fuel injection nozzles, jet engine nozzles,
engine valves, and engine cylinders.
We continue to investigate other coatings specifically designed to reduce coking. The figures shown here
illustrate the amount of coking occurring on various substrates and the table compares the performance of
Silcosteel®-AC, Silcosteel®, Sulfinert®, and prototype treatments. Silcosteel®-AC-treated
304 stainless steel shows dramatic reduction in coking vs. non-treated 304 stainless steel.
