The Bureau of Mines, under an interagency agreement with the U.S. Department of Energy (DOE), investigated the feasibility of coating the critical surfaces of valves by chemical vapor deposition (CVD). The purpose of the research was to increase the wear resistance of the valves for use in the abrasive and erosive environment of coal conversion and utilization processes. In-service testing of the CVD- tungsten ball seat was conducted at the DOE Morgantown Energy Technology Center (METC) in Morgantown, West Virginia. Tungsten CVD coatings were reproduced on nickel-plated carbon steels and stainless steels by the hydrogen reduction of the tungsten hexafluoride at 325 deg to 600 deg c. Tungsten-coated 6-, 10-, and 12-inch (0.15-, 0.25-, And 0.30-Meter) ball valve seats were prepared for METC evaluation in their low-btu coal gasification pilot plant. Use of the CVD- tungsten coated ball valve seat as a seal surface was determined to be satisfactory by METC under their process conditions. Little or no significant wear, other than a lapping effect, was noted on the valve seal surface after 1,230 cycles of operation.